text new page (beta)
English (pdf)
Article in xml format
Article references
Automatic translation
Send this article by e-mail
Cited by SciELO 
Similars in
SciELO 
Permalink
Ageratina Spach is the largest genus of the Mexican Asteraceae and the sixth largest genus of Mexican vascular plants (Villaseñor 2016, 2018). It comprises 167 species in Mexico, which are common members of humid mountain and conifer forests, as well as dry tropical forests and xerophytic shrublands of the country. They are mostly perennial or suffruticose herbs to large shrubs, with opposite, simple leaves, discoid heads and a pappus of persistent capillary bristles. The genus was resurrected from the synonymy of the traditional broad concept of Eupatorium L. by King & Robinson (1970). Because Eupatorium in its broad sense is a polyphyletic assemblage of several hundred species, it was narrowed to a more natural group of about 48 species, as summarized in King & Robinson (1987). Since then, preliminary phylogenetic analysis based on morphology (Bremer et al. 1994) and DNA sequences (Schilling et al. 1999, Ito et al. 2000, Robinson et al. 2009) have supported the narrow circumscription of Eupatorium and the resurrection of Ageratina. However, the broad concept of Eupatorium has been used in some Mexican floras, such “Flora-Novo Galiciana” (McVaugh 1984) and “Flora Fanerogámica del Valle de México” (Espinosa 2001).
In its narrow sense, a single species of Eupatorium occurs in Mexico, E. serotinum Michx., which has been reported from the state of Coahuila (Villarreal-Quintanilla 2001, Villaseñor 2016). Ageratina can be distinguished from Eupatorium sensu stricto by the structure of the involucre. In Ageratina it is composed of one or two series of bracts that are similar in size and shape, although some of the outermost bracts are usually smaller and shorter. However, in Eupatorium sensu stricto, the involucre is composed of numerous series of bracts that are progressively and conspicuously larger and broader in size. Also, the base of the style is hairy in Eupatorium s.s., but glabrous in Ageratina, among other differences.
Mexican Ageratina species are taxonomically difficult. This is due in part to the large number of species that makes specimen identification a complicated and time-consuming task. Also, few taxonomic keys are available and only that of Turner (1997) includes all the Mexican species; however, more than 20 new species have been described (Panero & Villaseñor 1998, Turner 2006, 2007, 2008, 2012) since the publication of that work. Moreover, many of the species are poorly circumscribed or lack clear species descriptions, so that it is often difficult to distinguish among very similar species. Likewise, key characteristics are not always present on herbarium specimens (for example, basal leaves or mature fruits). Furthermore, the nomenclature for many old species, such as those described in the nineteenth century, is usually complex and intricate, often holotypes were not designated, and the type material of Mexican taxa are usually located in foreign herbaria.
A different problem occurs when species remained unrecognized because they were placed in synonymy with another species. Turner (1997) considered Ageratina grandifolia (Regel) R.M. King & H. Rob. and A. rivalis (Greenm.) R.M. King & H. Rob. as synonyms of A. conspicua (Kunth & Bouché) R.M. King & H. Rob. However, the name of the latter is based on an illegitimate name (Eupatorium conspicuum Kunth & Bouché 1847, non Mart. ex Colla 1834), being A. grandifolia (based on Eupatorium grandifolium Regel) the correct name. In addition, Espinosa (2001) accepted A. rivalis (as Eupatorium rivale Greenm.) and described it as a shrub with terete stems and ovate leaves, among other features. Pruski & Robinson (2018) also accepted A. rivalis and similarly described it as a shrub. Recently, in addition to the shrub that can be referred to A. rivalis, we have observed in the Valley of Mexico a perennial to suffruticose herb, with large ovate-deltate leaf blades (almost 30 cm wide and long), and angulated branches with hollow internodes. The morphology of this entity did not match any of the species of the Valley of Mexico as treated by Espinosa (2001), but it would be keyed to A. grandifolia (as A. conspicua) according to Turner’s (1997) treatment. This would support the view that A. rivalis can be recognized as a distinct species from A. grandifolia, as in King & Robinson (1987), Espinosa (2001), and Pruski & Robinson (2018) treatments. Thus, we investigate further the morphology of these taxa to evaluate if there is additional evidence that support to recognize them as two distinct species, and if so, to clarify their circumscription, nomenclature and geographical distribution.
Materials and methods
Specimen images of type material of Ageratina grandifolia and A. rivalis were examined at the website GLOBAL PLANTS (Global Plants 2018) and pictures were requested from the Gray Herbarium at Harvard University. Protologues were also obtained, and bibliographic research to investigate the complete nomenclature history of these taxa was made. The Ageratina collection of the National Herbarium of Mexico (MEXU) was critically studied and additional observations of the morphology of the taxa in southern Mexico City, Guerrero, and State of Mexico were made. Specimens were also collected and deposited in MEXU. Detailed morphological descriptions were based on the material studied, and data on habitat, flowering, and geographic distribution were obtained from the herbarium sheet labels as well as from field observations. The geographical coordinates of the collection sites were obtained to elaborate distribution maps. A taxonomic key based on diagnostic features was made.
Results
After a meticulous analysis of the types and protologues of the basionyms of Ageratina grandifolia and A. rivalis, and the study of all the herbarium and living material, several morphological differences between these two entities were found. Ageratina grandifolia is a perennial herb woody at base to subshrub; its branches are subhexagonal, pilose to sparsely puberulent, green and often with dark-purplish stains, and hollow at internodes; the leaf blades are broadly ovate-deltate, up to almost 30 cm long and wide, with strongly serrate-decurrent bases; and the heads (5-6 mm long), corollas (3-4 mm long), and achenes (1.5-1.8 mm long) are slightly, but constantly shorter than those of A. rivalis (Table 1, Figures 1-4). On the other hand, A. rivalis is a shrub or subshrub, with terete branches, which are velutinous or tomentulose and whitened by the indument when young; however, they become puberulent and brownish or straw-colored and develop small, rounded lenticels; its internodes are solid and the leaf blades are broadly ovate-cordate to cordate (up to 17 cm long and 15 cm wide), without decurrent bases. As mentioned above, the heads, corollas and fruits of A. rivalis are longer than those of A. grandifolia. If mapped as two distinct taxa there are also differences in their geographic distributions. Ageratina rivalis seems to occur at the highlands of the Trans-Mexican Volcanic Belt of the states of Michoacán, Estado de México, Ciudad de México, Tlaxcala, Puebla, and Veracruz; it is also present at highlands in Guerrero, Oaxaca, and Chiapas (Figure 5). Besides, it is reported from Guatemala and Honduras (Pruski & Robinson 2018). Ageratina grandifolia seems to be confined to somewhat lower humid forests of Michoacán, Estado de México, Morelos, Ciudad de México, Hidalgo, Guerrero, and Oaxaca (Figure 5, Table 1).
Table 1 Morphological and biogeographical differences between Ageratina grandifolia and A. rivalis.
| A. grandifolia | A. rivalis | |
|---|---|---|
| Habit | Suffruticose herb to subshrub | Shrub or subshrub |
| Branch shape | Subhexagonal | Terete |
| Branch indumentum | Velutinous or tomentulous to sparsely puberulent | Pilose to glabrate |
| Internodes | Hollow | Solid |
| Leaf blade size (middle to lower leaves) | 9-28 × 10-29.5 cm | 10.5-17 × 8.5-15 cm |
| Leaf blade basal margins (middle to lower leaves) | 2-6.5 cm serrate-decurrent on the petiole | Non-decurrent on the petiole, rarely with an entire decurrent portion up to 1 cm |
| Head size | 5-6 × 3-4 mm | 7-10 × 4.5-6 mm |
| Corolla longitude | 3-4 mm | 4.5-5.5 mm |
| Achene longitude | 1.5-1.8 mm | 2-2.2 mm |
| Elevation | 1,600-2,600 m | 2,200-3,300 m |
| Distribution | Mexico (CdMx, Hgo, Gro, Méx, Mich, Mor, Oax). | Mexico (Chis., CdMx, Gro, Méx, Mich, Pue, Tlax, Ver), Guatemala, and Honduras. |
Figure 1 Ageratina rivalis. A. Young plant with widely ovate-cordate leaf blades. B. Lower woody branch with rounded, protruding lenticels. C. Young branch bearing opposite leaves. Note terete branch whitened by tomentulose or velutinous hairs and blades cordate at base. D. Internode cross section showing pith, cylindrical shape and protruding lenticels. E. Older heads.
Figure 2 Ageratina grandifolia. A. Plant growing on a patch of “Ciudad Universitaria, UNAM” campus. B. Branch with purplish spots. C. Internode cross section showing hollow pith and subhexagonal shape. D and E. Widely ovate-deltate leaf blade with subcordate and serrate-decurrent bases. F. flowering plant on a disturbed terrain at Km 3 of highway Picacho-Ajusco, southern Mexico City. G. Heads with exerted style branches.
Figure 4 Lectotype of Eupatorium conspicuum Kunth & Bouché Nom. Illeg. = Ageratina grandifolia (Regel) R.M. King & H. Rob. Note angulate and sulcate branches as well as serrate-decurrent leaf blades. Compare with figure 2.
Figure 5 Geographical distribution of Ageratina grandifolia and A. rivalis in Mexico. The latter occurs also in Guatemala and Honduras.
Both A. grandifolia and A. rivalis were classified in the subgenus Ageratina by King & Robinson (1987) and share the features of the subgenus: goblet-shaped white corollas with sparsely pilose lobes in the abaxial surface, columnar-clavate pentagonal achenes with a well-developed carpopodium, and uniseriate pappus bristles. They also have hirsutulous achenes, and non-glandular peduncules and involucres, and flower during the spring.
Discussion
Robinson (1923, 1926) first recognized some of the differences between the two taxa studied here, but considered them to be a single species with two varieties. He noticed that one taxon has hexangulate branches and decurrent leaf bases, in which the decurrent portion is serrate, while the other has terete branches and a non-serrate decurrent portion. However, there are additional morphological differences between these two taxa. One of the most notable are the hollow internodes in A. grandifolia vs solid in A. rivalis. There are also differences in leaf shape and size, indument and in the sizes of heads, corollas, and achenes, as well as in geographic distribution (Table 1). We interpret these additional morphological and biogeographical differences as evidence that two distinct species are involved, instead of a single polymorphic species as treated by Turner (1997) or a single species with two varieties as Robinson (1923, 1926). However, additional studies, especially using molecular data, are desirable to corroborate or refute this interpretation. Meanwhile, we agree with those who have treated A. grandifolia and A. rivalis as distinct species (King & Robinson 1987, Pruski & Robinson 2018). Since they were treated as a single species by Turner (1997) the circumscription and synonymy of the two species, but especially that of Ageratina grandifolia, requires clarification. Descriptions and complete synonymy for the two species are provided in the following account.
Taxonomy. Ageratina grandifolia (Regel) R.M. King & H. Rob., Phytologia 60: 80. 1986. Basionym: Eupatorium grandifolium Regel, Gartenflora 1: 102. 1852. Lectotype (designated here)—Illustration of Eupatorium grandifolium Regel, in Gartenflora 1: t. XII. 1852. Kyrstenia grandifolia (Regel) Greene, Leafl. Bot. Observ. Crit. 1: 9. 1903.
Ageratina conspicua R.M. King & H. Rob., Phytologia: 19: 213. 1970. Nomen novum for Eupatorium conspicuum Kunth & Bouché, Index Sem. (Berlin). 13. 1847, not E. conspicuum Mart. ex Colla, Herb. Pedem. 3: 283. 1834 [1835]. Lectotype (designated here)—Mexico: unknown locality, anonymous, June 1847, GH 00007166! (Figure 4).
Perennial herbs, woody at base or sometimes subshrubs, usually in clumps, up to 4 m tall, sparsely puberulent to pilose, young herbage and peduncles sometimes densely puberulent, but mostly glabrescent. Stem branches subhexagonal, clearly sulcate or grooved when pressed, green, often with dark-purplish spots, internodes hollow. Leaves decussate, petioles 7-10 cm long, blades broadly ovate-deltate, the uppermost sometimes ovate, (4.5-) 9-28 × (3-) 10-29.5 cm, bases subcordate to truncate and tapering upon the petioles, the serrate-decurrent portion (0.5-) 2-6.5 cm long, margins irregularly serrate, apex acuminate, palmately veined from slightly above base. Heads 5-6 × 3-4 mm, clustered in tight corymbiform arrays that together form a paniculiform-corymbiform capitulescence; involucre 4-5 mm high, the bracts acute to acuminate, sparsely puberulent to pilose, covering almost all length of the corollas. Florets 28-32 per head, corollas 3-4 mm long, achenes 1.5-1.8 mm long. Pappus bristles 2.8-3.8 mm long (Figures 2, 4).
Flowering. (February-) March to June.
Distribution. Endemic to Mexico, only known from Ciudad de México, Guerrero, Hidalgo, México, Michoacán, Morelos, and Oaxaca (Figure 5).
Elevation. 1,600-2,600 m.
Habitat. Shady places in slopes, ravines, banks, and roadsides, in humid mountain forest, Pinus forest and Quercus forest, often ruderal.
Uses. stomach discomfort (Olaiz, s.n. MEXU) and skin affections (Soto 6372 MEXU).
Common names. “Axihuitl” (Olaiz, s.n. MEXU), “Copal” (Hernández 4152 MEXU), “Quemada” (Soto 6372 MEXU).
Specimens examined. CIUDAD DE MEXICO: Hinojosa 485 (MEXU); Hinojosa 666 (MEXU); Quijano s.n. (MEXU). GUERRERO: Kruse 2454 (MEXU); Soto 8333 (MEXU); Rzedowski 16393 (MEXU). HIDALGO: Hernández 4152 (MEXU). MEXICO: Boege 1745 (MEXU); Matuda 30477 (MEXU); Matuda 30754 (MEXU). MICHOACAN: Cornejo 3710 (MEXU); Díaz 2105 (MEXU); Kishler 564 (MEXU); Soto 6333, 6372 (MEXU); MORELOS: Olaiz s.n. (MEXU); Dorado 1495 (MEXU); Espín 31 (MEXU); Espinosa 313 (MEXU); Pringle 8050 (MEXU).
Ageratina grandifolia is unique in the subgenus Ageratina by its subhexagonal branches with hollow internodes and large leaf blades that are almost 30 cm long and wide (Figures 2, 4; Table 1), and notably serrate-decurrent at the base. Ageratina rivalis has similar leaf blades (almost 20 cm long), but these tend to be more cordate in shape and non-decurrent or with an entire decurrent portion if any. Other differences are summarized in Table 1. Ageratina ramireziorum (J. Espinosa) B.L. Turner is similar to Ageratina grandifolia in habit and head sizes (5-7 mm long). The leaf blades of the former can reach up to 15 cm long and 10 cm wide according to Espinosa (1984, 2001), and they are also similar in being cuneate to decurrent at the base, but different in their more ovate to rhombic-ovate shape. Moreover, the decurrent portion is not serrate.
According to the protologue of the basionym of A. grandifolia, the plant was cultivated in Berlin from achenes that were found in a box that brought orchids from Guatemala; however, we could not find any records or herbarium sheets of this species from outside Mexico. So far, the southernmost records for this species are from Guerrero, Mexico, although Robinson (1926) cited it for the Sierra of San Felipe, in Oaxaca. The species was not cited from Mesoamerica (a region that includes southern Mexico and Central America) by King & Robinson (1990) nor more recently by Pruski & Robinson (2018). Also, A. grandifolia is reported from Mexico City for the first time, where it may be introduced. The oldest record of A. grandifolia for Mexico City is the collection of Quijano s.n. (MEXU) made in 2006. It is not reported for the Valley of Mexico (Espinosa 2001) nor in the checklist of the Asteraceae of “Pedregal de San Angel Ecological Reserve” (Céspedes et al. 2018). The species seems to be spreading in southern Mexico City, since we have observed individuals in several locations where they were absent previously. The species has been detected recently in basalt grounds on the campus of the National Autonomous University of Mexico, in the Bosque de Tlalpan National Park, and other sites in southern Mexico City (Figure 1).
Ageratina rivalis. (Greenm.) R.M. King & H. Rob., Phytologia 19: 216. 1970. Basionym: Eupatorium rivale Greenm., Zoë 5: 186. 1904. Lectotype (designated here)—Mexico: State of Mexico, Mt. Ixtaccihuatl, altitude 2,150 to 2,460 m, 1903, Purpus 213 GH 00007363! (Figure 3); Isolectotypes: UC 86357!, MO 2151192!, US 00130515!.
Eupatorium conspicuum Kunth & Bouché, Nom. Illeg. var. pueblense B.L. Rob., Contr. Gray Herb. 68: 12. 1923. Lectotype (designated here)—Mexico: State of Puebla, on rocky slopes, Boca del Monte, Mar 1908, Purpus 2992 (the larger sample to the right of the herbarium sheet) UC 112962!.
Ageratina skutchii (B.L. Rob.) R.M. King & H. Rob., Phytologia 19: 217. 1970. Basionym: Eupatorium skutchii B.L. Rob., Contr. Gray Herb. 104: 27. 1934. Type—Guatemala: Dept. Chimaltenango: open hillside, Santa Elena, alt. 2,400-2,700 m., Mar 25, 1933 Skutch 337 (holotype: US 00145724!).
Shrubs or subshrubs, in clumps, up to 3 m tall, densely puberulent when young, but glabrescent and corky when old, young petioles and branches often tomentulose or velutinous. Stem branches terete, rounded when pressed, often with small rounded protruding lenticels, internodes solid. Leaves decussate, petioles (1-) 4-12.5 cm long, blades broadly ovate-cordate to ovate, (6.5-) 10.5-17 × (4-) 8.5-15 cm, bases cordate to subcordate, sometimes rounded, rarely 1 cm tapering, margins irregularly serrate, apex acuminate, palmately veined from base or sometimes from slightly above the base in the uppermost leaves. Heads 7-10 × 4.5-6 mm, clustered in corymbiform arrays; involucre 5-6 mm, the bracts acute to acuminate, appressed-puberulent to glabrescent, covering half to almost all the length of the corollas. Florets 25-30 per head, corollas 4.5-5.5 mm, achenes 2-2.2 mm long. Pappus bristles 4.3-5.3 mm long (Figures 1 and 3).
Flowering. February to June.
Distribution. Mexico (Chiapas, Ciudad de México, Guerrero, Hidalgo, México, Michoacán, Morelos, Oaxaca, Puebla, and Veracruz) (Fig. 5), Guatemala and Honduras (Pruski & Robinson 2018).
Elevation. 2,200 to 3,300 m.
Habitat. Shady places in slopes, ravines, clearings, and roadsides, in mountain humid forest, Pinus forest, Pinus-Oak forest, and Abies forest.
Uses. For cough (Gómez 17 MEXU).
Common names. “Sak xaxib” (Tzeltzal) (Gómez 17 MEXU), “Putzil momol” (Pruski & Robinson 2018).
Specimens examined. CIUDAD DE MEXICO: Espinosa 2 (MEXU); Espinosa 23 (MEXU); Hinojosa 492, 645 (MEXU); Matuda 18808, 21023 (MEXU); Rzedowski 15582 (MEXU); Sandoval 12 (MEXU); Ventura 1013 (MEXU). CHIAPAS: Breedlove 9489 (MEXU); Gómez 17 (MEXU); Martínez 22552 (MEXU); Méndez 5801 (MEXU); Villaseñor 1224 (MEXU). GUERRERO: Calónico 7091 (MEXU); Dorado 1515 (MEXU); Panero 3949 (MEXU); Torres 1048 (MEXU). MEXICO: Boyas 529 (MEXU); Hinojosa 644, (MEXU); Lyonnet 2030, 3235 (MEXU); Matuda 28279 (MEXU); Miranda 4096 (MEXU); Rzedowski 34659, 37719 (MEXU); Yahara 1288 (MEXU). MICHOACAN: Álvarez 15255, 15185 (MEXU); Cornejo 94 (MEXU); Martínez 1445, 1595b (MEXU); Soto 6351, 18420, 8450 (MEXU). MORELOS: Salazar s.n. (MEXU). OAXACA: Calzada 20782, 22425 (MEXU); Gallardo 1032 (MEXU). PUEBLA: Boege 2735 (MEXU); Caamaño 6311 (MEXU). VERACRUZ: Barrie 1347 (MEXU); Nárave 406 (MEXU).
When Robinson (1923) published E. conspicuum Kunth & Bouche var. pueblense B.L. Rob. he was not aware that the name E. rivale Greenm. (1907) had already been applied to this taxon, nor that the name E. conspicuum of Kunth & Bouché (1847) was a later homonym of E. conspicuum Mart. ex Colla (1934). Later, Robinson (1926) treated E. grandifolium Regel as synonym of E. conspicuum of Kunth & Bouché. When King & Robinson (1970) transferred several species from Eupatorium to Ageratina, they also were not aware that their new combination, Ageratina conspicua (Kunth & Bouché) R.M. King & H. Rob., was based on an illegitimate name. However, the name A. conspicua R.M. King & H. Rob. was effectively published as a replacement name for E. conspicuum of Kunth & Bouché. Later, King & Robinson (1986) published A. grandifolia (Regel) R.M. King & H. Rob. thus, when these two taxa are considered taxonomic synonyms A. grandifolia has priority over A. conspicua.
In another matter, the herbarium sheet that here is designated as lectotype for Eupatorium rivale, was also labelled as lectotype by Turner in 1989, but he never published it. Also, the specimen selected here as the lectotype for E. conspicuum var. pueblense at UC has a small branch of A. pichinchensis (Kunth) R.M. King & H. Rob. as Robinson (1923) noticed, and the fragment and photo at GH come from that branch of A. pichinchensis. Also, the duplicate at US is entirely a sample of A. pichinchensis. This species occurs at similar elevations than A. rivalis and flowers at the same season but has more pubescent stems and branches and its heads are smaller (5 mm long). Another similar species, Ageratina isolepis (B.L. Rob.) R.M. King & H. Rob. is a suffruticous herb that shares with A. rivalis the terete branches with small rounded lenticels, solid internodes, and rounded to subcordate leaf blade bases. The leaf blades can reach up to 11 and 17 cm long respectively. In addition, A. isolepis occurs at similar elevations than A. rivalis in the Valley of Mexico (Espinosa 2001), and both flower during the spring. However, A. isolepis can be distinguished from A. rivalis by its shorter rounded involucral bracts (4-5 mm long), which cover half of the corollas, and smaller, more ovate to ovate-lanceolate leaves. Ageratina ramireziorum has also terete branches with solid internodes. It occurs at similar elevations than A. rivalis and also flowers in the spring. However, the heads are slightly shorter (5-7 mm long) and the leaf blades are ovate to rhombic-ovate. Turner (1997) states that both A. ramireziorum and A. isolepis may be the same species as A. photina (B.L. Rob.) R.M. King & H. Rob. Another species that sometimes is confused with these taxa is A. pazcuarensis (Kunth) R.M. King & H. Rob. This species is a perennial herb with ovate, non-decurrent leaf blades that flowers mostly on the fall and early winter. The heads of A. pazcuarensis seem to be similar in size (5-9 mm long) to those of A. rivalis. Last, we are following Pruski & Robinson (2018) in treating the Guatemalan A. skutchii (B.L. Rob.) R.M. King H. Rob., as synonym of A. rivalis; however, the whole complex requires further study to clarify the circumscription of these species. Meanwhile, the following key may help to recognize A. grandifolia and A. rivalis from similar species.
Key to Ageratina grandifolia, A. rivalis, and similar species
1a. Branches subhexagonal with hollow internodes, clearly grooved or sulcate when pressed; leaf blades with the bases strongly serrate-decurrent into the petioles (Figures 2, 4) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ageratina grandifolia
1b. Branches terete with pithy internodes, rounded or convex when pressed; leaf blades with the bases cordate to rounded or cuneate to entire-decurrent (but not serrate-decurrent) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (2)
2a. Stems copiously pilose to densely hirsutulous . . . . . . . . . . . . . . . . . . . . . . . . . Ageratina pichinchensis
2b. Stems sparsely pilose or puberulent to glabrous, sometimes tomentulose or velutinous when young . . . . . . . . . (3)
3a. Involucral bracts covering up to half of the corollas, their apices rounded . . . . . . . . . . . . . . . . . . . . . Ageratina isolepis
3b. Involucral bracts covering almost all corolla length, their apices acute to acuminate . . . . . . . . . . . . . . . . . . . . . . . . . (4)
4a. Leaves subpenninerved, with 2-4 veins from above the base of a main vein; heads mostly 4-5 mm long. . . . . . . . . . . . . . . . . . . . . . . . . Ageratina ramireziorum
4b. Leaves trinervate to palmately veined, with 3-5 main veins from the base or from slightly above the base; heads mostly 6-10 mm long . . . . . . . . . . . . . . . . . . . . . . . . . . . . (5)
5a. Shrubs or subshrubs, usually in clumps, the branches with small rounded protruding lenticels; flowering mostly from March to April . . . . . . . . . . . . . . . . . . . . . . Ageratina rivalis
5b. Perennial rhizomatous herbs, the branches herbaceous and without lenticels; flowering mostly from September to December . . . . . . . . . . . . . . . . . . . . . Ageratina pazcuarensis
Last, there were other species that were considered synonyms of A. grandifolia (as A. conspicua) by Turner (1997); namely A. purpusii (Brandegee) R.M. King & H. Rob., A. mariarum (B.L. Rob) R.M. King & H. Rob., and A. herrerae R.M. King & H. Rob. In the case of A. purpusii, which is endemic to Baja California Sur, it was actually recognized, keyed, and mapped as a distinct species by Turner (1997) and thus, the synonymy was probably a typo. Alternatively, Turner (1997) may have considered it a synonym of A. conspicua at first and later reversed, but omitted to eliminate the listing from under A. conspicua. As for A. herrerae and A. mariarum it seems best to recognize these two taxa as different species until the whole group is not revised. The former, which is endemic to Panama, has been recognized as a distinct species for the Flora of Mesoamerica (Pruski & Robinson, 2018). However, McVaugh (1984) stated that A. mariarum is perhaps conspecific to A. arsenei (B.L. Rob) R.M. King & H. Rob. Otherwise, A. mariarum is only known to the states of Jalisco, Nayarit, and Sinaloa.
This work is a contribution to the taxonomy and biogeography of the genus Ageratina in Mexico. This kind of works are desirable because the advances in the taxonomic and biogeographic knowledge of the species will improve our ability to conserve, monitor, and use them. Mexico stands out by having around 60 % of all the c. 250 Ageratina species, and 137 of them are endemic (Villaseñor 2018). Moreover, we have found reports of some medicinal uses for A. grandifolia and A. rivalis that require further study. According to Soto 6372 (MEXU), in the locality of “El Caracol,” near Morelia, Michoacán, a medicinal poultice is made with chopped leaves of A. grandifolia. This is relevant, since antibacterial substances and wound healing extracts have been obtained from other Mexican species that have been used in traditional medicine, such as A. arsenei (García-Sánchez et al. 2015) and A. pichinchensis (Romero-Cerecero et al. 2012). Furthermore, the protologue of A. grandifolia and its synonyms indicate this species was grown in the botanic garden of Berlin during the XIX century for its attractive capitulescences (Figure 2F-G). Therefore, this species has a potential as ornamental. On the other hand, other species such as A. adenophora R.M King & H. Rob. and A. riparia R.M. King H. Rob., are known to be problematic invasive plants elsewhere (Weber 2017). Fortunately, this has not been a problem for Mexico, although here we report the possible introduction and spreading of A. grandifolia in southern Mexico City. Accurate species determination is required to identify weed introductions and monitor their spreading. We hope this work, in which we clarify the morphology, nomenclature, and distribution of A. grandifolia and A. rivalis, and discuss how to distinguish them from similar species, is helpful for their identification.
