Synanthropic species of Asteraceae in Michoacán, Mexico

Especies sinantrópicas de Asteraceae en Michoacán, México

Resumen

Synanthropic vegetation thrives under human disturbance. Its composition is determined by climate and soil, but also by the type and intensity of disturbance (Rzedowski & Rzedowski, 2004). The species of these communities – weeds – are sometimes undesirable and can cause considerable economic harm (Hamill et al., 2004). However, they also have important ecological functions (Vibrans, 2016).

Weeds are commonly defined as “plants growing where they are not wanted, or undesirable” (Monaco et al., 2002); however, this definition is subjective, ambiguous, and not useful for understanding the biology of this group of plants. Here, we use the ecological concept: weeds are those species that can establish populations (obligatorily or facultatively) in places strongly disturbed by humans, without being cultivated. These may be cultivated fields (segetal or agrestal weeds) or ruderal environments (e.g., roadsides and field edges, surroundings of human settlements, urban vegetation, or vacant lots) (Baker, 1967; Rzedowski & Rzedowski, 2004). This definition of a weed species helps delimitation, though the degree of human disturbance remains a source of imprecision.

Synanthropic plants have unusual dynamics, as they converge, diverge, and evolve with crops; they depend on disturbance to stabilize their communities (Mahaut et al., 2020). However, many weeds inhabit not only environments disturbed by humans, but also by nature (e.g., water, landslides, tree falls, floods, hurricanes, fires, animals). Many species are even known from stable natural vegetation, although data on the proportions are lacking. Apparently, weedy species in natural vegetation are observed particularly in regions where weeds co-evolved with agriculture (Zohary, 1973), though good documentation is lacking.

Separating weeds from non-weeds is difficult, given the overlaps in nature, but it is a necessary task for studying these species as a group. Generally, classification as a weed is based on observations and unquantified herbarium data. It tends to be arbitrary and non-reproducible. Thus, it is desirable to develop clear criteria for classifying a species as a weed. Then, the ecology, biogeography, evolution, and interaction with human activities of these species can be explored. A significant number of native weeds have evolved in Mexico and its cultural region, Mesoamerica, which includes parts of Central America. According to Espinosa-García et al. (2004a, b), 2,814 species are considered weeds, of which 2,197 (78%) are native. 

Asteraceae Bercht. et J. Presl (Compositae Giseke nom. alt.) is representative of plant diversity in Mexico (Villaseñor et al., 2007). It is the most species-rich family in the country with 3,113 species and endemism of 63.9% (Villaseñor, 2018). Composites include a wide array of growth forms, which are distributed throughout the territory and all habitat types, including disturbed ones (Rzedowski, 1991). Based on morphological and molecular characters, the family is organized into tribes (Villaseñor, 1993); the most species-rich tribes in Mexico are Heliantheae, Eupatorieae, and Astereae (Villarreal & Villaseñor, 2004).

The state of Michoacán ranks fifth in Asteraceae richness, with 837 species. This richness is due to variations in climate, soil, and topography, as well as its position on the limits of several biogeographic regions (Villaseñor, 2018). Of these 837 species, one-third —282— have been reported previously as weeds (Villaseñor & Espinosa, 1998), positioning Michoacán as the state with the highest number of reported weeds, followed by Jalisco.

Here, we provide an updated list of Asteraceae weeds in Michoacán. The selection was based on standardized criteria. We quantify the proportion of growth forms, habitats, and biogeographic aspects for weeds that are endemic to Mexico, native but not restricted to Mexico, and introduced, as well as the floristic similarity of the weeds of Michoacán with other states of Mexico. In addition, the proportion of weeds per tribe is considered.

Materials and methods

Michoacán lies in the central-western part of Mexico (20°23’38.40” – 17°54’54.00” N, 100° 3’46.80” – 103°44’16.80” W), bordering Jalisco and Guanajuato to the north, Querétaro in the northeast, Estado de México and Guerrero to the east, the Pacific Ocean to the south, and Colima and Jalisco to the west (Fig. 1). It has a surface area of 58,599 km², 3% of the country (INEGI, 2015).

The Nearctic and Neotropical biogeographic regions converge in the study area (Conabio, 1997), as well as 4 biogeographic provinces, the Volcanic Belt, Pacific Coast, Balsas Depression, and the Sierra Madre del Sur (Fig. 1; Conabio, 1997). Also, it has a variable topography. As a result, it is one of the most phytodiverse states (Villaseñor & Ortiz, 2014), and the 5 main biomes recognized for Mexico occur in Michoacán.

Mountainous terrain covers 62% of the territory. The highest elevation is the Pico Tancítaro (3,857 m); the coastline is 208 km long (Flores & Priego, 2011). Average annual rainfall varies from 400 to 2,000 mm (Vidal-Zepeda, 1990). A warm sub-humid climate (Aw) dominates in the central and southern parts (García, 1998), with seasonally dry tropical forests occupying 50% of the state surface (Villaseñor & Ortiz, 2014). Luvisols are the most important soil type, followed by vertisols and another 14 soil types (INEGI, 2014, based on the World Reference Base for Soil Resources). Volcanic subsoil from the Cenozoic is found on 33% of the state’s surface; sedimentary and metamorphic rocks predominate in the south (Marín & Torres-Ruata, 1990). Rainfed and irrigated agriculture occupies about 35% of the area; in the tropics, cattle pastures are common and cover 6.2% of the state’s area (INEGI, 2016).

We used primary and secondary sources of information to identify weed species. Primary data sources were herbarium labels of field collections. Problems may arise in the acquisition and interpretation of label data since not all collectors include habitat information or only record the biome without indicating the degree of disturbance. The habitat information may be found in various label fields like observations, ecology, geoform, microenvironment, etc., which makes systematization more difficult (James et al., 2018; Moreno & Allkin, 1988).

Secondary data sources were mainly floras and taxonomic treatments that included information on habitat. The origin of this information was usually not specified; it might also have been based on herbarium specimens or simply on observations by the specialists (Appendix). 

Preliminary list. We worked with a database of all Asteraceae from Michoacán, managed and curated by one of the authors, an Asteraceae specialist (Villaseñor, unpublished data). It consisted of 13,641 records and 785 species (Fig. 2). The data derived mainly from the collections of the National Herbarium (MEXU) but included partial information from the herbaria CHAPA, CIMI, EBUM, ENCB, HUMO, IBUG, IEB, LL, MICH, MO, NY, SLPM, TEX, US, and XAL (herbaria acronyms according to Thiers, updated continuously). This data set was cross-checked with an unpublished list of known weeds in Mexico (Villaseñor & Espinosa, in preparation, an updated version of Villaseñor & Espinosa, 1998). This list was based on information from herbarium and literature sources, not all supported with specimens, with relatively broad and country-wide criteria. This process resulted in 426 species and 8,384 records of potential weeds in Michoacán. An additional search of the entire source database for habitat indications of either segetal or ruderal sites, but for species not found in the unpublished source list of weeds of Mexico, resulted in 4 more species and 37 records. Thus, the preliminary list of weeds of Michoacán consisted of 430 species and 8,421 records.

Final list. The preliminary list was critically reviewed to confirm or reject occurrence in human-made habitats in Michoacán. A species was included in the Michoacán weed list if at least 2 independent sources of information confirmed the ability to grow in highly disturbed environments. These sources could either be herbarium labels with clear indications of disturbed habitat or the description of the habitat in regionally relevant Floras.

The habitat information of the following Floras was used: Flora del Bajío y de Regiones Adyacentes (Cabrera & Rzedowski, 2018; García & Koch, 1995; Redonda-Martínez, 2013, 2016; Rzedowski et al., 2011; Rzedowski & Rzedowski, 1995, 1997, 2008; Villarreal, 2003; Villarreal et al., 2006), Flora Fanerogámica del Valle de México (Rzedowski et al., 2005), Flora Novogaliciana (McVaugh, 1984), the website Malezas de México (Vibrans, 2006 onwards), the work on Compositae in the synanthropic flora of Mexico (Rzedowski, 1993), and some additional publications, such as Flora Mesoamericana (Pruski & Robinson, 2018) and some taxonomic treatments of groups. 

Habitat information from labels was extracted for the 8,421 records of the preliminary list from IBdata v3 (IBdata, 2021). We excluded species that were only known as cultivated (Artemisia absinthium L. and Leucanthemum lacustre (Brot.) Samp.) or aquatic/subaquatic (Bidens laevis (L.) Britton, Sterns & Pogg., Jaegeria macrocephala Less., Leucosyris riparia (Kunth) Pruski & R.L. Hartm., Melampodium bibracteatum S. Watson, Solidago paniculata DC., and Tagetes persicifolius (Benth.) B.L. Turner), which resulted in 422 species and 8,360 records. Of these, only 6,539 records had habitat information. After an individual review of the label images on the IBData site, 1,739 additional indications of disturbed habitat were retrieved that had not been captured in the database.

The habitat information from the labels was classified into 2 types of environments. The first was predominantly natural or semi-natural (“NAT”) and the second was heavily disturbed (“WEED” for weeds). Semi-natural environments were included in the NAT category because disturbance is less intense and recurrent (Harlan & de Wet, 1965), although they may be the sources of some weed species (Vibrans, 2002), and generally have a composition of their own (Martorell et al., 2017; Rzedowski, 2006). The natural or semi-natural category included all types of forest, mangroves, natural palm groves, shrublands, as well as grasslands if the label did not indicate they were induced or planted, and high-elevation grasslands. Sites described as logged forests or forests with disturbed vegetation, etc., were also considered semi-natural vegetation. Some examples of label information that were considered to refer to semi-natural vegetation were the following: “heavily logged forest 15 to 20 years ago or so”, “low deciduous forest, disturbed, with Bursera, Caesalpinia, Lonchocarpus”, or “hillside with oak forest vegetation, forest in disturbance, probably replacing pine forest”.

Some other open vegetation types were also included in (semi-) natural vegetation. Examples were clearings or forest edges, cliffs, rocks or lava flows (“pedregal”), canyons, riverbanks, shores, wetlands, or volcanic craters. Examples of descriptions of open vegetation included in the natural category were “clearings in the middle of Abies forest”, “at the edge of moist forest”, “Pinus and Abies forest, on rocks”, “tropical deciduous forest, on outcrops of igneous rock”, or “oak forest on lava flow”.

Plants growing in human-transformed and heavily disturbed habitats were considered weedy. They included habitats described as segetal (“arvense”), crops, plantations, ruderal, roadsides, dam banks, canals or ditches, field edges, near crops, reforestation areas, pastures or induced grassland, urbanized sites or near houses, wastelands, embankments, or secondary vegetation without indicating a secondary forest. A total of 3,192 different habitat descriptions were assigned to the 2 classes (Supplementary material 1).

We found at least 2 collection records from clearly disturbed sites for 265 species (Fig. 2). Another 60 species were added based on one label and additional bibliographic support for that habitat. Others (32 species) were added even without clear label information, but with at least 2 independent literature references indicating that they may behave as agrestal or ruderal weeds in adjacent regions. We discarded 65 species that had information from only 1 source (e.g., literature or a single label without clear information). We always found literature support for single collections from a clearly disturbed habitat.

For the resulting 357 weed species, we gathered the following information from the literature: tribe (Funk et al., 2009), geographic distribution (native, but with distribution outside Mexico; endemic to Mexico; introduced), distribution by state in Mexico, geographic origin of the introduced species, as well as their life cycle and growth form (Appendix). Correlations were examined with linear regression analysis, and floristic similarity between states with the Sorensen-Dice similarity index, constructing a dendrogram with the UPGMA clustering method.

Results

From the preliminary list of 430 possible weed species of the Asteraceae, 73 (17%) were eliminated: 2 were only cultivated, 6 were aquatic or subaquatic, and 65 could not be documented as growing in disturbed environments in the state. As a result, 357 species were recognized as weeds for this state (Appendix).

Most synanthropic species also grew in less disturbed habitats; only 27% of all records were from clearly disturbed sites (Appendix), and a very low number, 2.7%, from crop fields (segetal weeds). Only 22% of the species (80; Appendix) grew mainly in disturbed sites and 16 species were found exclusively in disturbed sites. Of this number, 7 species had only 1 record, 5 species 2, 2 species 3 (Verbesina serrata Cav. and Conyza bonariensis (L.) Cronquist), and 1 species 5 records (Helminthoteca echioides (L.) Holub). Lactuca serriola L., an introduced species, was the most common weed growing exclusively in disturbed environments with 16 records.

Heliantheae had the highest number of weed species in Michoacán (83, Supplementary material 2); Liabeae (Sinclairia glabra (Hemsl.) Rydb.) and Mutisieae (Leibnitzia lyrata (D. Don) G.L. Nesom) had the least with only 1 species. For the state, no synanthropic species of the tribes Arctotideae, Calenduleae, Chaenactideae, Gochnatieae, Madieae, and Onoserideae were found. However, among the genera with the highest number of species, none belonged to the most species-rich tribe; the most outstanding were Melampodium L. (tribe Millerieae, with 19 species), Stevia Cav. (Eupatorieae, with 18 species), and Pseudognaphalium Kirp. (Gnaphalieae, with 14 species, Appendix).

The number of weed species per tribe correlated significantly with the total number of species of the tribe in Mexico (including non-weeds) (R² = 0.86, p = < 0.0001, Fig. 3). This correlation was even higher when comparing only species in Michoacán (R² = 0.89, p = < 0.0001). An exception was the tribe Eupatorieae with a relatively low proportion of weeds; this was also the tribe with the most species removed from the original list (26 species).

Native weed species (including endemics) dominated in Michoacán. Of the 357 accepted species, 342 (96%) were native and 150 (44%) endemic to Mexico. Heliantheae had the highest number of native and endemic species (83 and 42, respectively). Some tribes with relatively few species had a high proportion of endemic weeds, for example, Gnaphalieae and Cardueae (Table 1).

Table 1

Comparison of native and endemic Asteraceae weeds of Michoacán by tribe and those reported for Mexico.

Tribe	Native species in Mexico (weeds and non-weeds) (Villaseñor, 2018)	Endemic species in Mexico (weeds and non-weeds)	Native weeds in Michoacán (absolute number and percent)	Endemic weeds in Michoacán (absolute number and percent)
Heliantheae	649	464	83 (12.8)	42 (9.1)
Eupatorieae	619	433	49 (7.9)	19 (4.4)
Astereae	378	200	39 (10.3)	10 (5.0)
Millerieae	174	131	38 (21.8)	15 (11.5)
Tageteae	172	112	27 (15.7)	12 (10.7)
Coreopsideae	199	144	26 (13.1)	11 (7.6)
Senecioneae	219	165	22 (10.0)	16 (9.7)
Gnaphalieae	71	25	15 (21.1)	5 (20.0)
Vernonieae	72	47	8 (11.1)	6 (12.8)
Nassauvieae	97	83	7 (7.2)	5 (6.0)
Cardueae	46	28	7 (15.2)	6 (21.4)
Cichorieae	68	19	5 (7.4)	1 (5.3)
Bahieae	48	23	4 (8.3)	2 (8.7)
Anthemideae	14	3	2 (14.3)	0
Inuleae	12	15	2 (8.0)	0
Mutisieae	13	7	1 (7.7)	0
Neurolaeneae	28	19	2 (7.1)	0
Perityleae	51	40	2 (3.9)	0
Helenieae	44	14	2 (4.5)	0
Liabeae	25	15	1 (4.0)	0
Sum	3,012	1,987	342 (11.4)	150 (7.5)

 

Table 2

Introduced weeds in Michoacán by tribe and geographic origin, according to Villaseñor et al. (2012).

Tribe (number of species in Mexico/in Michoacán)	Species/origin/number of records
Anthemideae (9/4)	Cotula australis (Spreng.) Hook. f. /Oceania/5 Soliva anthemifolia (Juss.) Sweet /South America/3 Soliva sessilis Ruiz et Pav. /South America/3 Tanacetum parthenium (L.) Sch. Bip. /Asia, Europe/15
Cardueae (3/2)	Carthamus tinctorius L. /Europe/3 Cynara cardunculus L. /Africa, Asia and Europe/2
Cichorieae (7/6)	Helminthotheca echioides (L.) Holub /Africa, Europe/5 Lactuca serriola L. /Europe/16 Sonchus asper (L.) Hill /Asia, Europe/4 Sonchus oleraceus L. /Africa, Asia, Europe/18 Taraxacum officinale F.H. Wigg. /Europe/18 Tragopogon porrifolius L. /Asia, Europe/1
Gnaphalieae (1/1)	Pseudognaphalium luteoalbum (L.) Hilliard y B.L. Burtt /Asia, Europe/9
Senecioneae (2/2)	Senecio inaequidens DC. /Africa/19 Senecio vulgaris L. /Asia, Europe/3
Sum (22/15)

The pattern of endemic weeds was like that of all weeds, but they were found in fewer tribes (13). The correlation by tribe between the number of endemic weeds in Michoacán and all endemic species (weeds and non-weeds) in Mexico was high (R² = 0.77) and increased when only species endemic to Mexico and documented from Michoacán were considered (R² = 0.87).

We found 15 species of introduced or exotic weeds in the state (4.2% of all weedy species) distributed in 5 tribes (Table 2), all herbaceous. The tribes with the highest number of introduced species had few native species, particularly Cichorieae (5 genera, 6 introduced species, and only 5 native species). This tribe had only 1 species endemic to Mexico (Lactuca brachyrrhyncha Greenm.). Eleven of the 15 introduced species were native to Europe, and 7 of these were also distributed in Asia, and 3 in Africa. The South American species belonged to the tribe Anthemideae (Soliva anthemifolia (Juss.) Sweet and S. sessilis Ruiz & Pav.); Senecio inaequidens DC. came from Africa and Cotula australis (Spreng.) Hook. f. from Oceania.

Weed species native to Michoacán were shared mainly with neighboring states, particularly the Estado de México (324). States located in mountain ranges such as the Volcanic Belt and the Sierra Madre del Sur had the highest similarity (Figs. 4, 5). The number of shared species decreased towards the north; for example, Michoacán shared only 28 species with Baja California (Figs. 4, 5). Only a few species were known from all 32 federal states: Artemisia ludoviciana Nutt., Bidens pilosa L., Conyza canadensis (L.) Cronquist, and Symphyotrichum expansum (Poepp. ex Spreng.) G.L. Nesom.

The Mexican endemic weed species showed a pattern similar to widespread native weeds. However, Guerrero and Oaxaca had less floristic similarity. Michoacán shared the highest number of endemic weeds with the Estado de México and Jalisco (136 and 135 species, respectively, Fig. 6). The endemic species with the widest distribution was recorded in 28 states (Stevia origanoides Kunth). The state with the lowest number of shared species was Quintana Roo (only Montanoa grandiflora Alamán ex DC., also recorded in 22 states). 

Of the 150 weed species endemic to Mexico, 11 (3.4%) had a more restricted distribution and were limited to Michoacán and its neighboring states (Table 3). They belonged to 5 tribes, particularly Heliantheae. As with the endemic species, the closest relationship was with Jalisco (10 species) and Estado de México (6) (Fig. 7).

The weeds of Michoacán were mainly herbaceous (79%) (Table 4), a little more than half of them perennial (56.9%). Annual herbs occupied second place, and a small part was biannual or behaved as both annual and perennial. A sizeable proportion was woody (19.3%).

 

Discussion

We found no previous work that separated weeds and non-weeds in a standardized and therefore reproducible way. This may be due to the intrinsic difficulties of such a distinction (Lema, 2017). In nature, species live on gradients with different levels and types of adaptation to disturbance, both natural and human. These gradients make a clear separation between weeds and non-weeds difficult and will always be arbitrary to an extent; however, this arbitrariness is reduced with a clear definition of what is considered a weed. As mentioned in the introduction, here any species that could grow and establish populations in environments heavily disturbed by humans was considered a weed (Baker, 1974; Hanan & Vibrans, 2015; Rzedowski & Rzedowski, 2004).

 

 

Table 3

Asteraceae endemic weeds known only from Michoacán and neighboring states, based on Villaseñor (2016).

Tribe	Species (distribution by state in addition to Michoacán)
Coreopsideae	Bidens pringlei Greenm. (Col., Jal., Méx.)
	Chrysanthellum keilii B.L. Turner (Jal.)
	Chrysanthellum michoacanum B.L. Turner (Jal.)
Eupatorieae	Stevia nelsonii B.L. Rob. (Col., Gto., Jal., Mex., Qro.)
Heliantheae	Aldama michoacana (B.L. Turner et F.G. Davies) E.E. Schill. y Panero (Gro., Jal., Méx.)
	Lagascea aurea Stuessy (Col., Gto., Gro., Jal., Qro.)
	Montanoa imbricata V.A. Funk (Gro.)
	Verbesina pietatis McVaugh (Jal., Qro.)
Millerieae	Melampodium dicoelocarpum B.L. Rob. (Col., Gro., Jal., Mex.)
Tageteae	Flaveria robusta Rose (Col., Jal.)
	Pectis luckoviae D.J. Keil (Gro., Méx.)

Col. = Colima, Gro. = Guerrero, Gto. = Guanajuato, Jal. = Jalisco, Mex. = Estado de México, Qro. = Querétaro.

 

Table 4

Growth form and life cycle of the Michoacán weeds.

Growth form	Cycle	Number of species (%)
Tree	perennial	3 (0.8)
Shrub	perennial	66 (18.5)
Subshrub	perennial	5 (1.4)
Herb	perennial	129 (36.1)
Herb	annual or perennial	21 (5.9)
Herb	annual o biannual	8 (2.2)
Herb	annual	125 (35.0)
Sum		357 (100)

 

Other problems that had to be solved in a standardized way were lack of information, ambiguous information on herbarium labels or database records, as well as collection bias. Additionally, there were species in the gray or overlapping part of the gradient. These problems were solved by requiring 2 independent sources with information on their presence in heavily disturbed sites.

About one-sixth of the species cited as weeds in the literature from the region could not be confirmed as such. For example, some shrub species were part of pioneer vegetation and naturally disturbed sites but were not actually common components of transformed landscapes (Rzedowski, 2006). Most of the species removed from the preliminary list were Eupatorieae, a tribe with numerous shrubby species that can grow along forest edges or roadsides, without being very weedy (García et al., 2011).

A few excluded species were common weeds known from neighboring regions, but no specimens were found to document their presence in the state, perhaps due to insufficient collections. Examples are Ambrosia artemisiifolia L., Parthenium incanum Kunth, Grindelia subdecurrens DC. (Villaseñor and Espinosa, 1998), or Ageratum conyzoides L. (Villaseñor, 2016). The collection bias was also marked, as collectors generally avoid disturbed sites, especially cultivated areas (Carvajal, 1982). However, although weeds (and especially arborescent weeds) are under-collected, the proportion of collections in disturbed environments does tend to reflect the degree of synanthropy (Hanan et al., 2016).

The final list presented here contains species that can behave as weeds. It is probably incomplete, mainly because of insufficient data, a common problem with megadata (Hortal et al., 2015). The number is likely to increase with better documentation. However, we suggest that our criteria (2 independent, unambiguous, and relevant records from heavily disturbed environments) can serve as a model for future work. Additionally, we urge collectors and databases to improve habitat information. Information on the general vegetation type of a site is useful, but disturbance level should also be included in herbarium labels and database fields.

In Michoacán, almost half (43%) of all Asteraceae were synanthropic. The proportion for the whole country is only 17% (Villaseñor, 2018; Villaseñor & Espinosa García, 1998). This can be explained by differences in the size of the distribution areas —weedy species are much more widespread on average than non-weedy ones (Espinosa-García et al., 2004a). More than half of the Michoacán weeds were registered nationally as weeds for the same reason (219 of 411; Rzedowski, 1993).

This study adds more than a hundred Asteraceae species of weeds to those previously reported for the state (Villaseñor & Espinosa, 1998) and for all of Mexico (Rzedowski, 1993) (132 and 138 more, respectively). Seven species considered by Villaseñor and Espinosa (1998) were not confirmed, although their presence was documented. They were not included because they lacked evidence for synanthropic behavior in the state.

There are no comparable data from other federal states of Mexico, except for Querétaro (Colmenero et al., 2001). These authors reported 81 weed species of the family, that is, only a quarter of those recorded for Michoacán. Up to now, Michoacán is the state with the highest number of Asteraceae weeds in Mexico, confirming a statement by Villaseñor and Espinosa (1998).

Few weed species (4.5%) were documented exclusively from heavily disturbed environments, and most of them with few records. Of these, Conyza bonariensis (L.) Cronquist and Simsia lagasciformis DC. had previously been shown to be restricted to disturbed environments (Rzedowski, 1993). Only a quarter of the species had more than half of the collections in this type of environment. This partially reflected the above-mentioned collection bias towards more natural environments (Carvajal, 1982). However, it also shows that in Mexico, ruderal and agrestal species are embedded in the vegetation of the adjacent landscape and depend at least partially on functional traits of species with non-weedy behavior (Bourgeois et al., 2019; Metcalfe et al., 2019; Munoz et al., 2020).

Similar results have been reported in the Near East, where most weeds are also found in other vegetation types (Holzner, 1978; Zohary, 1973). The results contrast with the more evident separation between weeds and non-weeds in central and northern Europe (Holzner, 1978) or the United States (Sutherland, 2004). This may perhaps be explained by the history of agriculture. In its region of origin, species preadapted to anthropized environments coevolved as crop weeds, then migrated along with the crops. The communities gradually impoverished but specialized, depending on environmental filters such as crop or soil type and climate (Fried et al., 2010; Smart et al., 2006).

Generally, taxonomic groups are related, having characteristics in common as well as predictive value (McNeill, 1976). So, if weeds are required to have certain characteristics (Baker, 1974), one would expect them to be concentrated in certain tribes. However, the results of this study do not show such concentration.

The weedy species were distributed in 20 of the 26 tribes of Compositae known from Mexico (Villaseñor, 2018); the 6 tribes without synanthropic species were species-poor. Generally, in Michoacán roughly half of the species in each tribe were weedy, though with some variation; endemic weeds also had a relatively constant proportion. The percentages at the national level were also proportional (range between 3.9% and 21.8%, with an average of 11.6%), but lower because of the more restricted distribution areas of non-weedy species on average (Espinosa-García et al., 2004a). The only exception was Cichorieae, a tribe with few species but with a high proportion of weeds and exotics (Villaseñor, 2018).

Some authors have proposed that weeds require specific characteristics to compete and colonize new environments (Baker, 1974), which can, however, be highly variable (Basu et al., 2004; Hanan et al., 2016). This study shows that weeds can develop in different tribes independently, perhaps because the functional spaces of weeds are not clearly delimited from non-weeds (Bourgeois et al., 2019).

Under the criteria used in this work, the species-rich tribe Eupatorieae had a relatively low proportion of weeds. It consists mainly of perennial herbs or shrubs, often in forest edges or clearings (García et al., 2011), where differentiation between weeds and non-weeds is particularly difficult. Also, the most species-rich tribes did not necessarily contain the most weed-rich genera; Melampodium (tribe Millerieae), for example, was the genus with the largest number of weedy species (19) but belonged to a medium-sized tribe; it grows widely in transformed landscapes at different levels of disturbance (Hanan et al., 2016). Rzedowski (1993) highlights a group of incipient weed genera, which were indeed well represented as weeds in Michoacán, e.g., Stevia Cav. (18), Brickellia Raf. (9), and Erigeron L. (7).

In Michoacán, native weeds predominated (Rzedowski, 1991). Almost half (44%) of them were endemic to Mexico (at a national level this percentage reaches 63.9% according to Villaseñor [2018]), but this was to be expected, given the generally larger distribution area of weeds.

The proportion of introduced species (4.2%) was much lower than that reported by Espinosa-García et al. (2004b) for the whole Mexican weed flora, with 28%. The differences are probably explained by differences in the proportion of introduced species between families (Brassicaceae, Fabaceae, or Poaceae have a considerably higher share of exotics; Villaseñor & Magaña [2006]). Most introduced species of the Asteraceae were native to Europe and the Mediterranean, which may be explained by the history of commerce (Villaseñor & Espinosa-García, 2004). All were herbs, as occurs in other floras (Arianoutsou et al., 2010; Garcillán et al., 2013; Weber et al., 2008), perhaps because this life form is well-represented in weeds and has some (pre-) adaptation to disturbed habitats.

The floristic composition reflects the history of biotic exchanges between regions and shared ecological conditions (Garcillán et al., 2013). Comparisons provide information on possible factors that determine such similarities. The weed flora of Michoacán was most similar to that of neighboring states, a similarity that decreased as distance increased (Nekola & White, 1999). However, we found stronger similarity with the western states located along the Volcanic Belt and the Sierra Madre del Sur (Guerrero and Oaxaca). They included regions known for their early settlements and agriculture (Zizumbo & Colunga, 2008), high proportions of endemism (Estrada-Márquez et al., 2021), and the greatest richness of Asteraceae (Villaseñor et al., 2005).

There were relatively few (11) endemic weed species with restricted distribution, but it is interesting that they exist at all. Rzedowski (2020) in the Flora del Bajío y de regiones adyacentes highlights some of them as species restricted to the Balsas Depression (Chrysanthellum keilli B.L. Turner and C. michoacanum B.L. Turner) or to the Volcanic Belt (Verbesina pietatis McVaugh). Estrada-Márquez et al. (2021) consider Bidens pringlei Greenm. and Verbesina pietatis as restricted to the same areas. It is likely that these species are examples of relatively recently evolved weed species.

Weed species in Michoacán were mostly herbs (79%). Short life cycles facilitate growth in frequently disturbed open environments (Díaz et al., 2016). However, a considerable number of woody plants could also grow in highly disturbed sites, as occurs in other parts of the world, such as France (Fried et al., 2009). They should be examined in more detail.

In temperate regions, ruderals are mostly perennial hemicryptophytes or geophytes whereas agrestals are typically annual therophytes (Bourgeois et al., 2019; Holzner, 1978), a pattern that was repeated here. The better representation of ruderal areas (roadsides, etc.) in the collections possibly increased the representation of perennials (63%), as cultivated areas (segetals) were severely under-collected.

Lack of quality information and collection biases limit the correct classification of species into weedy and non-weedy. However, herbarium data are good approximations when the information is reliable (Hanan et al., 2016). This study is based on fully verified data, especially taxonomic identification. It is likely that other species that were not included due to lack of evidence will have to be added in the future. 

This study proposes criteria to identify weedy species in a systematic, reproducible way and includes a species list based on these criteria. Michoacán harbors a high number of native and endemic Asteraceae weed species, with a very low proportion of introduced plants. Most species grow in both disturbed sites and natural vegetation. This indicates the existence of a wide variety of biological traits that allow plants to live in transformed environments, reflected also by the relatively similar proportion of weeds in the different tribes. Floristic similarities with neighboring states point to close relationships within the western and southern parts of Mexico, a region with a long history of disturbance associated with human settlements and agriculture.

Acknowledgements

We are especially grateful to Enrique Ortíz Bermúdez and the students of the Asteraceae Laboratory, UNAM, and the Ethnobotany Laboratory, Colegio de Postgraduados, Campus Montecillo, for their support. This work was financed by grant #545819 from the Comisión Nacional de Ciencia y Tecnología, Mexico (Conacyt), for the doctoral studies of the first author. 

Appendix. List of weed species of Asteraceae in Michoacán. The superscript indicates the references. Native: species considered native to the region but distributed outside of Mexico; endemic: endemic to Mexico; endemic with restricted distribution: species only distributed in Michoacán and adjacent federal states; introduced: origin outside of the geographical region.

Species	Tribe	Growth form	Biogeographical status: native, endemic, endemic with restricted distribution, introduced	Total number of records	Records from disturbed habitats
Achillea millefolium L.1,2,3f,4,5	Anthemideae	Perennial herb	Native	10	4
Acmella radicans (Jacq.) R.K. Jansen1,2,3g	Heliantheae	Annual herb	Native	25	10
Acmella repens (Walter) Rich.1,2,3g,4	Heliantheae	Perennial herb	Native	54	19

Appendix.
Species	Tribe	Growth form	Biogeographical status: native, endemic, endemic with restricted distribution, introduced	Total number of records	Records from disturbed habitats
Acourtia fruticosa (La Llave) B.L. Turner	Nassauvieae	Shrub	Endemic	32	5
Acourtia humboldtii (Less.) B.L. Turner	Nassauvieae	Annual or perennial herb	Endemic	23	4
Acourtia moschata (La Llave) DC.	Nassauvieae	Subshrub	Endemic	12	2
Acourtia reticulata (Lag. ex D. Don) Reveal & R.M. King2	Nassauvieae	Perennial herb	Native	31	7
Adenophyllum aurantium (L.) Strother Tageteae		Perennial herb	Endemic	10	2
Adenophyllum cancellatum (Cass.) Villarreal1,3h	Tageteae	Annual herb	Endemic	8	5
Adenophyllum porophyllum (Cav.) Hemsl.3h	Tageteae	Annual herb	Native	22	8
Adenophyllum pulcherrimum (Strother) Villarreal3h	Tageteae	Annual herb	Endemic	1	1
Ageratina adenophora (Spreng.) R.M. King & H. Rob.2,4	Eupatorieae	Shrub	Native	40	14
Ageratina areolaris (DC.) Gage ex B.L. Turner	Eupatorieae	Shrub	Native	73	4
Ageratina brevipes (DC.) R.M. King & H. Rob.	Eupatorieae	Shrub	Endemic	10	3
Ageratina deltoidea (Jacq.) R.M. King & H. Rob.1,2,4,5	Eupatorieae	Perennial herb	Endemic	3	0
Ageratina glabrata (Kunth) R.M. King & H. Rob.	Eupatorieae	Shrub	Endemic	48	6
Ageratina mairetiana (DC.) R.M. King & H. Rob.	Eupatorieae	Shrub	Native	92	12
Ageratina petiolaris (Moc. & Sessé ex DC.) R.M. King & H. Rob.2,4	Eupatorieae	Shrub	Endemic	24	10
Ageratina pichinchensis (Kunth) R.M. King & H. Rob.1,2	Eupatorieae	Shrub	Native	6	1
Ageratum corymbosum Zuccagni5	Eupatorieae	Perennial herb	Native	84	27
Ageratum houstonianum Mill.1,2,5,6	Eupatorieae	Annual herb	Native	1	0
Aldama buddlejiformis (DC.) E.E. Schill. & Panero3d	Heliantheae	Perennial herb	Endemic	11	4
Aldama dentata La Llave1,2,3g,4,5	Heliantheae	Annual herb	Native	41	25
Aldama ghiesbreghtii (Hemsl.) E.E. Schill. & Panero	Heliantheae	Perennial herb	Endemic	54	4
Aldama linearis (Cav.) E.E. Schill. & Panero4	Heliantheae	Perennial herb	Endemic	16	11
Aldama michoacana (B.L. Turner & F.G. Davies) E.E. Schill. & Panero5	Heliantheae	Annual herb	Endemic with restricted distribution	24	11
Aldama pachycephala (DC.) E.E. Schill. & Panero4	Heliantheae	Perennial herb	Endemic	12	7
Aldama palmeri (A. Gray) E.E. Schill. & Panero	Heliantheae	Annual herb	Endemic	8	3
Alloispermum integrifolium (DC.) H. Rob.1	Millerieae	Shrub	Native	24	3
Alloispermum scabrum (Lag.) H. Rob.3g	Millerieae	Perennial herb	Native	58	6
Ambrosia canescens A. Gray2,3g,4,5	Heliantheae	Perennial herb	Endemic	2	1
Ambrosia cumanensis Kunth1,2	Heliantheae	Perennial herb	Native	24	15
Aphanostephus ramosissimus DC.1,2,4,5	Astereae	Annual or perennial herb	Native	14	7
Archibaccharis asperifolia (Benth.) S.F. Blake2,4	Astereae	Perennial herb	Native	26	4
Archibaccharis hirtella (DC.) Heering	Astereae	Subshrub	Native	29	3
Archibaccharis schiedeana (Benth.) J.D. Jacks.	Astereae	Subshrub	Native	16	3
Archibaccharis serratifolia (Kunth) S.F. Blake1,4	Astereae	Perennial herb	Native	44	3
Artemisia ludoviciana Nutt.1,2,3f,4,5	Anthemideae	Perennial herb	Native	28	10
Astranthium orthopodum (B.L. Rob. & Fernald) Larsen2,5	Astereae	Annual or biannual herb	Endemic	52	19
Baccharis conferta Kunth4	Astereae	Shrub	Native	57	9
Baccharis heterophylla Kunth2,5	Astereae	Shrub	Native	106	17
Baccharis multiflora Kunth	Astereae	Shrub	Native	34	4
Baccharis pteronioides DC.2,4,5	Astereae	Subshrub	Native	30	15
Baccharis salicifolia (Ruiz & Pav.) Pers.1,2,5	Astereae	Shrub	Native	23	10
Baccharis sordescens DC.4	Astereae	Shrub	Endemic	2	1
Baccharis thesioides Kunth	Astereae	Subshrub	Native	7	2
Baccharis trinervis (Lam.) Pers.2,5	Astereae	Shrub	Native	6	2
Baltimora geminata (Brandegee) Stuessy2,5,13	Heliantheae	Annual herb	Native	1	0
Barkleyanthus salicifolius (Kunth) H. Rob. & Brettell1,2,4,5	Senecioneae	Shrub	Native	80	32
Bidens aequisquama (Fernald) Sherff3g	Coreopsideae	Perennial herb	Endemic	70	8
Bidens anthemoides (DC.) Sherff1,2,3g,4	Coreopsideae	Annual or perennial herb	Endemic	17	0
Bidens aurea (Aiton) Sherff1,2,3g,4,5	Coreopsideae	Perennial herb	Native	56	21
Bidens bigelovii A. Gray1,2,3g,4,5	Coreopsideae	Annual herb	Native	20	2
Bidens odorata Cav.1,2,3g,4,5	Coreopsideae	Annual herb	Native	72	27
Bidens pilosa L.1,2,3g,4,5	Coreopsideae	Annual herb	Native	14	4
Bidens pringlei Greenm.5	Coreopsideae	Perennial herb	Endemic with restricted distribution	6	2
Bidens riparia Kunth2,5,6	Coreopsideae	Annual herb	Native	5	0
Bidens serrulata (Poir.) Desf.1,2,3g,4	Coreopsideae	Annual herb	Endemic	10	1
Bidens triplinervia Kunth1,2,3g,4,5	Coreopsideae	Perennial herb	Native	55	10
Blumea viscosa (Mill.) V.M. Badillo2,3c,5	Inuleae	Perennial herb	Native	5	1
Brickellia diffusa (Vahl) A. Gray2,5	Eupatorieae	Annual herb	Native	10	1
Brickellia eupatorioides (L.) Shinners	Eupatorieae	Perennial herb	Native	4	3
Brickellia filipes B.L. Rob.2,5	Eupatorieae	Annual herb	Endemic	1	0
Brickellia glandulosa (La Llave) McVaugh	Eupatorieae	Shrub	Native	5	2
Brickellia paniculata (Mill.) B.L. Rob.2,5	Eupatorieae	Shrub	Native	4	0
Brickellia pedunculosa (DC.) Harc. & Beaman	Eupatorieae	Perennial herb	Endemic	31	4
Brickellia pendula (Schrad.) A. Gray	Eupatorieae	Shrub	Endemic	18	2
Brickellia secundiflora (Lag.) A. Gray1,2	Eupatorieae	Shrub	Endemic	26	8
Brickellia veronicifolia (Kunth) A. Gray2,4	Eupatorieae	Shrub	Native	1	0
Calea ternifolia Kunth2	Neurolaeneae	Shrub	Native	6	2
Calea urticifolia (Mill.) DC.3g	Neurolaeneae	Shrub	Native	14	5
Calyptocarpus vialis Less.1,2,3g,4,5	Heliantheae	Perennial herb	Native	5	3
Calyptocarpus wendlandii Sch. Bip.1,2	Heliantheae	Perennial herb	Native	1	1
Carminatia recondita McVaugh1	Eupatorieae	Annual herb	Native	22	7
Carthamus tinctorius L.2,3a	Cardueae	Annual herb	Introduced	3	1
Chromolaena collina (DC.) R.M. King & H. Rob.2	Eupatorieae	Shrub	Native	43	9
Chromolaena odorata (L.) R.M. King & H. Rob.1,2	Eupatorieae	Perennial herb	Native	26	12
Chrysanthellum indicum DC.2,3g,5	Coreopsideae	Annual herb	Native	14	3
Chrysanthellum keilii B.L. Turner2,12	Coreopsideae	Annual herb	Endemic with restricted distribution	2	1
Chrysanthellum michoacanum B.L. Turner2,5	Coreopsideae	Annual herb	Endemic with restricted distribution	2	0
Chromolaena pulchella (Kunth) R.M. King & H. Rob.	Eupatorieae	Perennial herb	Endemic	27	9
Cirsium acantholepis (Hemsl.) Petr.3a,4,5	Cardueae	Perennial herb	Endemic	4	1
Cirsium anartiolepis Petr.	Cardueae	Perennial herb	Endemic	40	3
Cirsium ehrenbergii Sch. Bip.3a,4	Cardueae	Perennial herb	Endemic	42	3
Cirsium pascuarense (Kunth) Spreng.4	Cardueae	Perennial herb	Endemic	6	4
Cirsium rhaphilepis (Hemsl.) Petr.1,2,3a,4	Cardueae	Perennial herb	Endemic	12	6
Cirsium velatum (S. Watson) Petr.2,3a,5	Cardueae	Perennial herb	Endemic	25	6
Conyza bonariensis (L.) Cronquist1,2,4,5	Astereae	Annual herb	Native	3	3
Conyza canadensis (L.) Cronquist1,2,3j,4,5	Astereae	Annual herb	Native	32	22
Conyza coronopifolia Kunth1,2,4,5	Astereae	Annual herb	Native	44	14
Conyza laevigata (Rich.) Pruski2,5	Astereae	Annual herb	Native	2	0
Conyza microcephala Hemsl.2,4	Astereae	Perennial herb	Endemic	14	4
Conyza sumatrensis (Retz.) E. Walker6	Astereae	Annual herb	Native	1	1
Coreopsis petrophiloides B.L. Rob. & Greenm.	Coreopsideae	Shrub	Endemic	23	2
Cosmos bipinnatus Cav.1,2,3g,4,5	Coreopsideae	Annual herb	Native	50	25
Cosmos carvifolius Benth.	Coreopsideae	Perennial herb	Endemic	7	2
Cosmos crithmifolius Kunth2,4	Coreopsideae	Perennial herb	Native	26	2
Cosmos diversifolius Otto2,4	Coreopsideae	Perennial herb	Native	2	1
Cosmos pacificus Melchert1	Coreopsideae	Annual herb	Endemic	24	8
Cosmos parviflorus (Jacq.) Pers.1,2,3g,4,5	Coreopsideae	Annual herb	Native	21	5
Cosmos scabiosoides Kunth1,5	Coreopsideae	Perennial herb	Endemic	91	14
Cosmos sulphureus Cav.1,2,3g,5	Coreopsideae	Annual herb	Native	17	7
Cotula australis (Spreng.) Hook. f.1,2,3f,4,5	Anthemideae	Annual herb	Introduced	5	3
Cynara cardunculus L.1,2,3a	Cardueae	Perennial herb	Introduced	2	2
Dahlia coccinea Cav.1,3g	Coreopsideae	Perennial herb	Native	137	29
Dahlia neglecta Saar	Coreopsideae	Perennial herb	Endemic	10	2
Dahlia sorensenii H.V. Hansen & Hjert.11	Coreopsideae	Perennial herb	Native	14	1
Delilia biflora (L.) Kuntze2,3g,5	Heliantheae	Annual herb	Native	17	4
Dendroviguiera sphaerocephala (DC.) E.E. Schill. & Panero	Heliantheae	Shrub	Endemic	10	5
Dugesia mexicana (A. Gray) A. Gray1,2,3g,4	Heliantheae	Perennial herb	Endemic	1	0
Dyssodia papposa (Vent.) Hitchc.1,2,3h,4,5	Tageteae	Annual herb	Native	22	10
Dyssodia pinnata (Cav.) B.L. Rob.2,4,5	Tageteae	Perennial herb	Endemic	8	2
Dyssodia tagetiflora Lag.1,2,3h,5	Tageteae	Perennial herb	Endemic	39	18
Eclipta prostrata (L.) L.1,2,3g,5	Heliantheae	Annual herb	Native	23	6
Erechtites hieracifolius (L.) Raf. ex DC.1,2	Senecioneae	Annual herb	Native	2	2
Eremosis tomentosa (Lex.) Gleason3e	Vernonieae	Shrub	Endemic	34	11
Eremosis triflosculosa (Kunth) Gleason2,5	Vernonieae	Shrub	Native	3	1
Eremosis villaregalis (Carvajal) Pruski3e	Vernonieae	Shrub	Endemic	10	2
Erigeron delphinifolius Willd.2,4,5	Astereae	Annual or perennial herb	Native	38	12
Erigeron galeottii (A. Gray ex Hemsl.) Greene2,4	Astereae	Perennial herb	Endemic	34	1
Erigeron karvinskianus DC.2	Astereae	Perennial herb	Native	9	6
Erigeron longipes DC.1,2,4,5	Astereae	Perennial herb	Native	67	27
Erigeron polycephalus (Larsen) G.L. Nesom5	Astereae	Perennial herb	Endemic	3	2
Erigeron pubescens Kunth1	Astereae	Perennial herb	Native	6	2
Erigeron velutipes Hook. & Arn.2,5	Astereae	Annual herb	Endemic	10	4
Euphrosyne partheniifolia DC.1,4	Heliantheae	Annual or perennial herb	Endemic	4	1
Flaveria robusta Rose2,5	Tageteae	Shrub	Endemic with restricted distribution	1	1
Flaveria trinervia (Spreng.) C. Mohr1,2,3i,4,5	Tageteae	Annual herb	Native	10	4
Fleischmannia pycnocephala (Less.) R.M. King & H. Rob.1,2	Eupatorieae	Perennial herb	Native	2	0
Fleischmannia sonorae (A. Gray) R.M. King & H. Rob.	Eupatorieae	Perennial herb	Native	15	3
Florestina lobata B.L. Turner	Bahieae	Annual herb	Endemic	5	3
Florestina pedata (Cav.) Cass.1,2,3i,4,5	Bahieae	Annual herb	Native	39	14
Galeana pratensis (Kunth) Rydb.2,3i,5	Perityleae	Annual herb	Native	47	14
Galinsoga longipes Canne1,3g	Millerieae	Annual herb	Endemic	5	2
Galinsoga parviflora Cav.1,2,3g,4,5	Millerieae	Annual herb	Native	109	43
Galinsogeopsis scopulorum (M.E. Jones) I.H. Lichter-Marck 1,2,3i,5	Perityleae	Annual herb	Native	2	0
Gamochaeta americana (Mill.) Wedd.1,2,5	Gnaphalieae	Annual or biannual herb	Native	53	17
Gamochaeta falcata (Lam.) Cabrera2,4,5	Gnaphalieae	Annual herb	Native	4	1
Grindelia inuloides Willd.2,4,5	Astereae	Perennial herb	Endemic	5	2
Guardiola mexicana Bonpl.1,5	Millerieae	Perennial herb	Endemic	53	9
Guardiola tulocarpus A. Gray5	Millerieae	Shrub	Endemic	6	2
Helenium mexicanum Kunth2,3i,4	Helenieae	Annual or biannual herb	Native	17	10
Helenium quadridentatum Labill.2,3i,5	Helenieae	Annual or biannual herb	Native	1	1
Helianthus annuus L.1,2,3g,4	Heliantheae	Annual herb	Native	3	2
Heliopsis annua Hemsl.2,3g,5	Heliantheae	Annual herb	Endemic	14	10
Heliopsis buphthalmoides (Jacq.) Dunal2,6	Heliantheae	Perennial herb	Native	8	1
Heliopsis procumbens Hemsl.2,5	Heliantheae	Perennial herb	Endemic	11	1
Helminthotheca echioides (L.) Holub1,2,4	Cichorieae	Annual or perennial herb	Introduced	5	5
Heterosperma pinnatum Cav.1,2,3g,4,5	Coreopsideae	Annual herb	Native	36	11
Heterotheca inuloides Cass.1,2,4,5	Astereae	Perennial herb	Endemic	25	5
Hieracium abscissum Less.3k	Cichorieae	Perennial herb	Native	53	2
Hieracium crepidispermum Fr.3k	Cichorieae	Perennial herb	Native	16	5
Hieracium schultzii Fr.3k,4	Cichorieae	Perennial herb	Native	22	5
Hymenostephium cordatum (Hook. & Arn.) S.F. Blake2,3g	Heliantheae	Perennial herb	Native	32	2
Hymenostephium tenuis (A. Gray) E.E. Schill. & Panero2,5	Heliantheae	Annual herb	Native	6	1
Jaegeria hirta (Lag.) Less.1,2,3g,4,5	Millerieae	Annual herb	Native	94	19
Koanophyllon albicaule (Sch. Bip. ex Klatt) R.M. King & H. Rob.6	Eupatorieae	Shrub	Native	4	1
Lactuca brachyrrhyncha Greenm.10	Cichorieae	Perennial herb	Endemic	3	1
Lactuca serriola L.1,2,3k,4	Cichorieae	Annual or perennial herb	Introduced	16	16
Laennecia filaginoides DC.2,4,5	Astereae	Annual herb	Native	21	2
Laennecia gnaphalioides (Kunth) Cass.2	Astereae	Annual or perennial herb	Native	4	2
Laennecia schiedeana (Less.) G.L. Nesom4	Astereae	Annual or perennial herb	Native	30	3
Laennecia sophiifolia (Kunth) G.L. Nesom1,2,4	Astereae	Annual herb	Native	23	10
Lagascea aurea Stuessy	Heliantheae	Annual herb	Endemic with restricted distribution	22	3
Lagascea decipiens Hemsl.2,5	Heliantheae	Shrub	Native	3	1
Lagascea helianthifolia Kunth1,5	Heliantheae	Shrub	Native	69	13
Lagascea mollis Cav.1,2,5	Heliantheae	Annual herb	Native	18	14
Lasianthaea aurea (D. Don) K.M. Becker2,3d,5	Heliantheae	Perennial herb	Endemic	23	6
Lasianthaea ceanothifolia (Willd.) K.M. Becker3d,6	Heliantheae	Shrub	Endemic	11	2
Lasianthaea crocea (A. Gray) K.M. Becker1,3d	Heliantheae	Shrub	Endemic	11	1
Lasianthaea helianthoides DC.2,5	Heliantheae	Shrub	Endemic	6	1
Lasianthaea macrocephala (Hook. & Arn.) K.M. Becker1,5	Heliantheae	Shrub	Endemic	5	1
Lasianthaea palmeri (Greenm.) K.M. Becker2,3d,5	Heliantheae	Perennial herb	Endemic	6	2
Leibnitzia lyrata (D. Don) G.L. Nesom2,6	Mutisieae	Perennial herb	Native	5	0
Melampodium americanum L.2,3d,5	Millerieae	Annual herb	Native	30	13
Melampodium aureum Brandegee	Millerieae	Perennial herb	Endemic	15	3
Melampodium dicoelocarpum B.L. Rob.5	Millerieae	Annual herb	Endemic with restricted distribution	9	3
Melampodium divaricatum (Rich.) DC.1,2,3d,4,5	Millerieae	Annual herb	Native	87	47
Melampodium glabrum S. Watson2,3d,4	Millerieae	Annual herb	Endemic	15	6
Melampodium gracile Less.2,3d,5	Millerieae	Annual herb	Native	11	3
Melampodium linearilobum DC.2,5	Millerieae	Annual herb	Native	18	10
Melampodium longifolium Cerv. ex Cav.2,4	Millerieae	Annual herb	Endemic	4	1
Melampodium longipes (A. Gray) B.L. Rob.5,6	Millerieae	Annual herb	Endemic	1	0
Melampodium longipilum B.L. Rob.	Millerieae	Annual herb	Native	4	2
Melampodium microcephalum Less.2,3d,5	Millerieae	Annual herb	Native	40	18
Melampodium montanum Benth.	Millerieae	Perennial herb	Native	27	4
Melampodium paniculatum Gardner2,6	Millerieae	Annual herb	Native	1	0
Melampodium perfoliatum (Cav.) Kunth2,3d,4,5	Millerieae	Annual herb	Native	63	39
Melampodium pilosum Stuessy5	Millerieae	Perennial herb	Endemic	33	12
Melampodium repens Sessé & Moc.1,2,3d,4	Millerieae	Annual herb	Endemic	14	5
Melampodium sericeum Lag.1,2,3d,5	Millerieae	Annual herb	Native	66	42
Melampodium strigosum Stuessy2,3d	Millerieae	Annual herb	Native	3	1
Melampodium tenellum Hook. & Arn.2,5	Millerieae	Annual herb	Endemic	1	0
Melanthera nivea (L.) Small1,2,3d,5	Heliantheae	Perennial herb	Native	3	1
Mikania cordifolia (L. f.) Willd.2,6	Eupatorieae	Perennial herb	Native	1	0
Mikania micrantha Kunth2,5	Eupatorieae	Perennial herb	Native	1	0
Milleria quinqueflora L.1,2,3d,5	Millerieae	Annual herb	Native	19	9
Montanoa bipinnatifida (Kunth) K. Koch1,2,3d	Heliantheae	Shrub	Endemic	10	3
Montanoa frutescens Mairet ex DC.2,3d,4,5	Heliantheae	Shrub	Endemic	7	1
Montanoa grandiflora Alamán ex DC.2,3d	Heliantheae	Shrub	Endemic	36	8
Montanoa imbricata V.A. Funk2,3d,5	Heliantheae	Shrub	Endemic with restricted distribution	4	1
Montanoa karwinskii DC.2,5	Heliantheae	Shrub	Endemic	6	1
Montanoa leucantha (Lag.) S.F. Blake2,3d,5	Heliantheae	Shrub	Native	23	4
Montanoa tomentosa Cerv.2,3d,4,5	Heliantheae	Shrub	Native	3	0
Packera sanguisorbae (DC.) C. Jeffrey4	Senecioneae	Perennial herb	Endemic	90	7
Packera toluccana (DC.) W.A. Weber & A. Löve4	Senecioneae	Perennial herb	Endemic	67	4
Parthenium bipinnatifidum (Ortega) Rollins1,2,3d,4,5	Heliantheae	Annual herb	Native	9	8
Parthenium hysterophorus L.1,2,4,5	Heliantheae	Annual herb	Native	13	10
Pectis haenkeana (DC.) Sch. Bip.9	Tageteae	Annual or perennial herb	Endemic	3	1
Pectis leavenworthii Standl.	Tageteae	Perennial herb	Endemic	10	5
Pectis linifolia L.2	Tageteae	Annual herb	Native	14	4
Pectis luckoviae D.J. Keil	Tageteae	Annual herb	Endemic with restricted distribution	19	9
Pectis prostrata Cav.1,2,3h,5	Tageteae	Annual herb	Native	13	4
Pectis uniaristata DC.5	Tageteae	Annual herb	Native	7	2
Pinaropappus roseus (Less.) Less.1,2,3k,4,5	Cichorieae	Perennial herb	Native	48	12
Piqueria pilosa Kunth	Eupatorieae	Perennial herb	Endemic	50	3
Piqueria triflora Hemsl.2,5	Eupatorieae	Annual herb	Endemic	9	1
Piqueria trinervia Cav.1,2,5	Eupatorieae	Perennial herb	Native	56	11
Plectocephalus rothrockii (Greenm.) D.J.N. Hind1,2,3a,6	Cardueae	Annual or perennial herb	Native	2	1
Pluchea carolinensis (Jacq.) G. Don1,2	Inuleae	Shrub	Native	17	3
Podachaenium eminens (Lag.) Sch. Bip.2,5,6	Heliantheae	Tree	Native	9	0
Porophyllum linaria (Cav.) DC.2	Tageteae	Annual herb	Endemic	2	1
Porophyllum macrocephalum DC.1,2,3h,5	Tageteae	Annual herb	Native	18	3
Porophyllum punctatum (Mill.) S.F. Blake	Tageteae	Shrub	Native	22	10
Porophyllum viridiflorum (Kunth) DC.	Tageteae	Shrub	Endemic	44	9
Psacalium amplifolium (DC.) H. Rob. & Brettell	Senecioneae	Perennial herb	Endemic	6	2
Psacalium cirsiifolium (Zucc.) H. Rob. & Brettell5	Senecioneae	Perennial herb	Endemic	20	3
Psacalium megaphyllum (B.L. Rob. & Greenm.) Rydb.5	Senecioneae	Perennial herb	Endemic	28	4
Psacalium palmeri (Greene) H. Rob. & Brettell5	Senecioneae	Perennial herb	Endemic	18	2
Psacalium peltatum (Kunth) Cass.	Senecioneae	Perennial herb	Endemic	41	6
Psacalium platylepis (B.L. Rob. & Seaton) H. Rob. & Brettell5	Senecioneae	Perennial herb	Endemic	2	1
Psacalium sinuatum (Cerv.) H. Rob. & Brettell4	Senecioneae	Perennial herb	Endemic	44	11
Pseudelephantopus spicatus (Aubl.) Rohr2,3e,5	Vernonieae	Perennial herb	Native	15	10
Pseudognaphalium attenuatum (DC.) Anderb.2,6	Gnaphalieae	Perennial herb	Native	12	1
Pseudognaphalium bourgovii (A. Gray) Anderb.5	Gnaphalieae	Annual herb	Endemic	8	2
Pseudognaphalium canescens (DC.) Anderb.2,5	Gnaphalieae	Perennial herb	Native	5	1
Pseudognaphalium chartaceum (Greenm.) Anderb.2,4,5	Gnaphalieae	Annual or biannual herb	Endemic	13	3
Pseudognaphalium conoideum (Kunth) Anderb.2,4	Gnaphalieae	Annual herb	Endemic	4	1
Pseudognaphalium greenmanii (S.F. Blake) Anderb.6	Gnaphalieae	Annual or biannual herb	Native	3	1
Pseudognaphalium inornatum (DC.) Anderb.2,4,5	Gnaphalieae	Annual or perennial herb	Endemic	20	6
Pseudognaphalium liebmannii (Sch. Bip. ex Klatt) Anderb.2,5	Gnaphalieae	Annual or perennial herb	Native	36	3
Pseudognaphalium luteoalbum (L.) Hilliard & B.L. Burtt1,2,4	Gnaphalieae	Annual herb	Introduced	9	3
Pseudognaphalium oxyphyllum (DC.) Kirp.5	Gnaphalieae	Annual or perennial herb	Native	21	4
Pseudognaphalium roseum (Kunth) Anderb.4	Gnaphalieae	Perennial herb	Native	32	5
Pseudognaphalium semilanatum (DC.) Anderb.2,5	Gnaphalieae	Annual herb	Endemic	21	3
Pseudognaphalium stramineum (Kunth) Anderb.2,4,5	Gnaphalieae	Annual herb	Native	3	0
Pseudognaphalium viscosum (Kunth) Anderb.1,2,4,5	Gnaphalieae	Annual or biannual herb	Native	15	4
Psilactis asteroides A. Gray2,4,5	Astereae	Annual or perennial herb	Native	9	5
Psilactis brevilingulata Sch. Bip. ex Hemsl.1,2,4,5	Astereae	Annual or perennial herb	Native	16	5
Roldana angulifolia (DC.) H. Rob. & Brettell	Senecioneae	Shrub	Native	89	7
Roldana barba-johannis (DC.) H. Rob. & Brettell4	Senecioneae	Shrub	Native	43	3
Roldana candicans (Née) Villaseñor, S. Valencia & Coombes	Senecioneae	Perennial herb	Native	59	2
Roldana heracleifolia (Hemsl.) H. Rob. & Brettell2,5	Senecioneae	Perennial herb	Endemic	35	9
Roldana lobata La Llave4	Senecioneae	Perennial herb	Endemic	18	1
Roldana mexicana (McVaugh) H. Rob. & Brettell5	Senecioneae	Perennial herb	Endemic	45	4
Roldana sessilifolia (Hook. & Arn.) H. Rob. & Brettell4	Senecioneae	Perennial herb	Endemic	31	4
Roldana suffulta (Greenm.) H. Rob. & Brettell	Senecioneae	Perennial herb	Endemic	20	2
Sabazia humilis (Kunth) Cass.1,2,4	Millerieae	Annual herb	Endemic	4	1
Salmea oligocephala Hemsl.3d	Heliantheae	Shrub	Endemic	6	2
Sanvitalia ocymoides DC.5	Heliantheae	Annual herb	Native	1	1
Sanvitalia procumbens Lam.1,2,4,5	Heliantheae	Annual herb	Native	17	11
Schkuhria pinnata (Lam.) Kuntze1,2,3i,4,5	Bahieae	Annual herb	Native	70	29
Schkuhria schkuhrioides (Link & Otto) Thell.1,2,3i,4,5	Bahieae	Annual herb	Endemic	11	5
Sclerocarpus divaricatus (Benth.) Hemsl.2,5	Heliantheae	Annual herb	Native	9	2
Sclerocarpus multifidus Greenm.	Heliantheae	Annual herb	Endemic	3	2
Sclerocarpus papposus (Greenm.) Feddema2,8	Heliantheae	Annual herb	Endemic	8	1
Sclerocarpus uniserialis (Hook.) Hemsl.1,2	Heliantheae	Annual or perennial herb	Native	16	12
Senecio callosus Sch. Bip.5	Senecioneae	Perennial herb	Native	60	7
Senecio cinerarioides Kunth4	Senecioneae	Shrub	Endemic	27	3
Senecio inaequidens DC.1	Senecioneae	Perennial herb	Introduced	19	5
Senecio stoechadiformis DC.2,4,5	Senecioneae	Perennial herb	Endemic	127	27
Senecio vulgaris L.1,2,4	Senecioneae	Annual herb	Introduced	3	1
Sigesbeckia agrestis Poepp. & Endl.1,2,5	Millerieae	Annual herb	Native	20	8
Sigesbeckia jorullensis Kunth1,2,4	Millerieae	Perennial herb	Native	43	7
Simsia amplexicaulis (Cav.) Pers.1,2,4,5	Heliantheae	Annual herb	Native	25	13
Simsia annectens S.F. Blake1	Heliantheae	Annual herb	Endemic	18	6
Simsia foetida (Cav.) S.F. Blake2	Heliantheae	Annual herb	Native	9	4
Simsia lagasciformis DC.2,5	Heliantheae	Annual herb	Native	2	2
Simsia sanguinea A. Gray1,2	Heliantheae	Perennial herb	Native	6	3
Sinclairia glabra (Hemsl.) Rydb.3b	Liabeae	Shrub	Native	11	4
Smallanthus maculatus (Cav.) H. Rob.1,2,4,5	Millerieae	Perennial herb	Native	14	4
Soliva anthemifolia (Juss.) Sweet2,3f	Anthemideae	Annual or perennial herb	Introduced	3	2
Soliva sessilis Ruiz & Pav.	Anthemideae	Annual herb	Introduced	3	2
Sonchus asper (L.) Hill1,2,3k,4,5	Cichorieae	Annual or perennial herb	Introduced	4	3
Sonchus oleraceus L.1,2,3k,4,5	Cichorieae	Annual or perennial herb	Introduced	17	10
Stevia aschenborniana Sch. Bip.1,7	Eupatorieae	Annual herb	Endemic	2	0
Stevia caracasana DC.2,5	Eupatorieae	Perennial herb	Native	28	5
Stevia connata Lag.1,6	Eupatorieae	Perennial herb	Native	7	0
Stevia elatior Kunth1,5	Eupatorieae	Perennial herb	Native	24	3
Stevia incognita Grashoff	Eupatorieae	Perennial herb	Native	3	2
Stevia lucida Lag.6	Eupatorieae	Shrub	Native	15	1
Stevia micrantha Lag.1,2	Eupatorieae	Annual herb	Native	12	6
Stevia monardifolia Kunth	Eupatorieae	Perennial herb	Endemic	50	3
Stevia nelsonii B.L. Rob.2,5	Eupatorieae	Shrub	Endemic with restricted distribution	6	0
Stevia origanoides Kunth	Eupatorieae	Perennial herb	Endemic	33	4
Stevia ovata Willd.2	Eupatorieae	Perennial herb	Native	35	3
Stevia porphyrea McVaugh	Eupatorieae	Perennial herb	Endemic	3	2
Stevia salicifolia Cav.	Eupatorieae	Shrub	Native	23	3
Stevia serrata Cav.1,2,4,5	Eupatorieae	Perennial herb	Native	74	18
Stevia subpubescens Lag.4	Eupatorieae	Shrub	Endemic	27	2
Stevia tomentosa Kunth1	Eupatorieae	Perennial herb	Endemic	2	1
Stevia trifida Lag.	Eupatorieae	Perennial herb	Endemic	11	2
Stevia viscida Kunth2,5	Eupatorieae	Perennial herb	Native	24	3
Symphyotrichum expansum (Poepp. ex Spreng.) G.L. Nesom2,4,5	Astereae	Annual herb	Native	44	18
Symphyotrichum moranense (Kunth) G.L. Nesom1	Astereae	Perennial herb	Native	20	4
Tagetes erecta L.1,2,3h	Tageteae	Annual herb	Native	106	42
Tagetes filifolia Lag.1,2,3h,4,5	Tageteae	Annual herb	Native	36	11
Tagetes foetidissima DC.1,2,3h,4,5	Tageteae	Annual herb	Native	29	7
Tagetes lucida Cav.1,2,3h,4,5	Tageteae	Perennial herb	Native	81	23
Tagetes lunulata Ortega1,2,3h,4,5	Tageteae	Annual herb	Endemic	36	16
Tagetes micrantha Cav.1,2,3h,4,5	Tageteae	Annual herb	Native	26	6
Tagetes subulata Cerv.2,3h,5	Tageteae	Annual herb	Native	14	6
Tagetes tenuifolia Cav.	Tageteae	Annual herb	Native	9	3
Tanacetum parthenium (L.) Sch. Bip.1,2,3f	Anthemideae	Perennial herb	Introduced	12	4
Taraxacum officinale F.H. Wigg.1,2,3k,4,5	Cichorieae	Perennial herb	Introduced	18	9
Tithonia diversifolia (Hemsl.) A. Gray1,2,5	Heliantheae	Perennial herb	Native	5	3
Tithonia rotundifolia (Mill.) S.F. Blake1,2,5	Heliantheae	Annual herb	Native	29	13
Tithonia tubiformis (Jacq.) Cass.1,2,4,5	Heliantheae	Annual herb	Native	22	15
Tragopogon porrifolius L.1,6	Cichorieae	Annual or biannual herb	Introduced	1	1
Tridax coronopifolia (Kunth) Hemsl.1,2,4,5	Millerieae	Annual or perennial herb	Endemic	20	12
Tridax mexicana A.M. Powell2,5	Millerieae	Perennial herb	Endemic	4	3
Tridax platyphylla B.L. Rob.2,5	Millerieae	Annual herb	Native	17	6
Tridax procumbens L.1,2,5	Millerieae	Perennial herb	Native	2	1
Tridax trilobata (Cav.) Hemsl.1,2,4	Millerieae	Annual herb	Endemic	12	7
Trigonospermum annuum McVaugh & Lask.2,5	Millerieae	Annual herb	Native	18	6
Trigonospermum melampodioides DC.	Millerieae	Perennial herb	Native	30	6
Trixis inula Crantz2,4,5	Nassauvieae	Shrub	Native	1	0
Trixis mexicana Lex.1,2	Nassauvieae	Shrub	Endemic	36	6
Trixis michuacana Lex.5	Nassauvieae	Shrub	Endemic	19	2
Verbesina breedlovei B.L. Turner2	Heliantheae	Shrub	Endemic	4	1
Verbesina crocata (Cav.) Less.1,2	Heliantheae	Tree	Native	13	6
Verbesina fastigiata B.L. Rob. & Greenm.2	Heliantheae	Shrub	Endemic	48	15
Verbesina montanoifolia B.L. Rob. & Greenm.2,5	Heliantheae	Shrub	Endemic	35	6
Verbesina myriocephala Sch. Bip. ex Klatt2,6	Heliantheae	Perennial herb	Native	5	1
Verbesina pietatis McVaugh	Heliantheae	Perennial herb	Endemic with restricted distribution	8	2
Verbesina serrata Cav.1	Heliantheae	Shrub	Endemic	3	3
Verbesina sphaerocephala A. Gray2	Heliantheae	Shrub	Endemic	42	14
Verbesina tetraptera (Ortega) A. Gray4	Heliantheae	Perennial herb	Endemic	14	3
Verbesina virgata Cav.4	Heliantheae	Shrub	Endemic	19	1
Vernonanthura cordata (Kunth) H. Rob.	Vernonieae	Tree	Endemic	34	9
Vernonanthura liatroides (DC.) H. Rob.	Vernonieae	Perennial herb	Endemic	19	7
Vernonanthura serratuloides (Kunth) H. Rob.2	Vernonieae	Perennial herb	Endemic	23	7
Vernonia alamanii DC.2,3e	Vernonieae	Perennial herb	Endemic	112	22
Viguiera dentata (Cav.) Spreng.1,2,4,5	Heliantheae	Perennial herb	Native	27	12
Wedelia acapulcensis Kunth2,6	Heliantheae	Perennial herb	Native	12	0
Xanthium strumarium L.1,2,4,5	Heliantheae	Annual herb	Native	5	3
Xanthocephalum benthamianum Hemsl.5	Astereae	Annual herb	Endemic	2	1
Xanthocephalum centauroides Willd.	Astereae	Annual herb	Endemic	2	2
Zinnia americana (Mill.) Olorode & A.M. Torres2,5	Heliantheae	Annual herb	Native	11	4
Zinnia angustifolia Kunth2,5	Heliantheae	Perennial herb	Endemic	1	0
Zinnia bicolor (DC.) Hemsl.2,5	Heliantheae	Annual herb	Endemic	2	0
Zinnia elegans Jacq.1,2	Heliantheae	Annual herb	Native	32	16
Zinnia flavicoma (DC.) Olorode & A.M. Torres2,5	Heliantheae	Annual herb	Endemic	19	8
Zinnia haageana Regel1,2,5	Heliantheae	Annual herb	Endemic	36	17
Zinnia peruviana (L.) L.1,2,4,5	Heliantheae	Annual herb	Native	35	13
Zinnia purpusii Brandegee1	Heliantheae	Annual herb	Endemic	2	2
Zinnia zinnioides (Kunth) Olorode & A.M. Torres5	Heliantheae	Annual herb	Endemic	3	1

1 Vibrans (2006),2 Rzedowski (1993), 3a García and Koch (1995), 3b Redonda-Martínez (2013), 3c Redonda-Martínez (2016), 3d Rzedowski et al. (2011), 3e Rzedowski and Rzedowski (1995), 3f Rzedowski and Rzedowski (1997), 3g Rzedowski and Rzedowski (2008), 3h Villarreal (2003), 3i Villarreal et al. (2006), 3j Silva-Sáenz (2017), 3k Rzedowski (1997), 4 Rzedowski et al. (2005), 5 McVaugh (1984), 6 Pruski and Robinson (2018), 7 Villagómez-Flores et al. (2018), 8 Villaseñor and Hinojosa-Espinosa (2011), 9 Villarreal et al. (2008), 10 Flores-Huitzil et al. (2020), 11 Castro-Castro et al. (2015), 12 Turner (1988), and 13 Stuessy (1973).

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