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Cyperaceae (Poales) are a cosmopolitan, monophyletic family, the third largest among Monocots after Orchidaceae and Poaceae and the seventh among angiosperms, with about 5,500 species (Muasya et al. 2009a, b, Escudero & Hipp 2013, Govaerts et al. 2015). Their origins are in the late Cretaceous (Escudero & Hipp 2013) in what is now South America (Spalink et al. 2016). Known as sedges, they superficially resemble grasses or rushes, Juncaceae being its sister group (Jones et al. 2007).
Cyperaceae possess a unique combination of cytogenetical features: holokinetic chromosomes, possibility of inverted meiosis, and pseudomonad development (asymmetric tetrads). These characteristics favor karyotype differentiation for agmatoploidy (fission), symploidy (fusion), and polyploidy (Luceño & Guerra 1997) as well as a broad variation in chromosome number (2n = 4 to 2n ≥ 200) (Roalson 2008). Chromosomes evolve more dynamically in sedges than in any other group of flowering plants and this, in turn, favors a rapid evolution and diversification and a high level of endemism in some groups (Hipp et al. 2006, 2009).
Sedges occur in a variety of habitats, being common in moist areas like wetlands, marshes, swamps, riverbanks, ponds and sandbank environments (Goetghebeur 1998), but they are well represented also in dry areas in many kinds of vegetation, including xerophytic scrub. Cyperaceae include several worldwide distributed genera. The largest genus is Carex L., one of the most species rich genera among angiosperms (Reznicek 1990a), with about 1,983 species, or nearly 2,000 species with the merger of satellite genera (The Global Carex Group 2015, 2016).
Most species have a great environmental value (e.g., as habitat and food for wild species and soil stabilizers) and many have ethnobotanical and economic importance (Bye 1979, Diego-Pérez 1995, Simpson & Inglis 2001, Ludlow-Wiechers & Diego-Pérez 2002). Some are among the world’s worst weeds, e.g., Cyperus rotundus L., C. esculentus L. and Fimbristylis miliacea (L.) Vahl (Bryson & Carter 2008). Other species are used as food, as the tuberous nodules on the rhizomes of Cyperus esculentus and Eleocharis dulcis (Burm. f.) Trin. ex Hensch., or the rhizomes and tender young shoots of three species of Schoenoplectus (Rchb.) Palla, that were used by Native Americans (Rink & Licher 2015). Among the ornamentals are Cyperus alternifolius L., C. involucratus Rottb. and C. papyrus L. Several species of Cyperus L., Eleocharis R. Br. and Schoenoplectus are used in phytoremediation (Rice et al. 1997, Wang et al. 2010).
Among the taxonomic reviews of Cyperaceae for Mexico or larger regions including the country are those for Abildgaardia, Bulbostylis & Fimbristylis (Kral 1971), Carex (Hermann 1974), Cyperus (Tucker 1994), Eleocharis (Svenson 1929, 1932, 1934, 1937, 1939, 1957), Fuirena (Kral 1978), Lipocarpha (Goetghebeur & Van den Borre 1989), Rhynchospora (Kükenthal 1949, 1950a, b, 1951, Thomas 1984, 1992, 1994), Scleria (Core 1936, 1965), as well as sections of Carex (Reznicek 1986, 1993a, Reznicek & González-Elizondo 2001a, 2001b), Cyperus (Denton 1978), and Hypolytrum (Alves et al. 2015). Treatments of Cyperaceae for regional floras in Mexico include those in Flora Novo-Galiciana (McVaugh 1993, Reznicek 1993b, Tucker & McVaugh 1993); Flora Mesoamericana (Adams 1994); Yucatan (Diego-Pérez 1995); Guerrero (Diego-Pérez 1997); Veracruz (Diego-Pérez 2008, 2012) and Valle de México (González-Elizondo 2001).
Additional references for the family in Mexico include descriptions of new taxa (e.g., Reznicek 1982, 1990b, González-Elizondo 1985, Tucker 1982, 1986, Cochrane 1981, Kral & Thomas 1986, Reznicek & González-Elizondo 1995, 1997, 1999, 2001a, González-Elizondo & Reznicek 1997, 2005, Roalson 1999, Strong & González-Elizondo 2000, Ramos-Álvarez & Diego-Pérez 2002, González-Elizondo et al. 2005, 2007a, 2009, Reznicek et al. 2007, Rosen 2009, Saarela et al. 2010, Gómez-Sánchez et al. 2012, LeBlond et al. 2015); data on taxonomy or distribution (González-Elizondo & Rzedowski 1983, 1984, Strong 1993, 1994, 2003, González-Elizondo & Peterson 1997, Diego-Pérez et al. 2001, González-Elizondo & Tena-Flores 2000, González-Elizondo et al. 2002, 2007b, Reznicek & González-Elizondo 2008, Rosen et al. 2007, 2008a,b, Herbario CICY 2010 onwards), and uses or bioprospecting of sedges for pharmacology or phytoremediation (Flores-Tavizón et al. 2005, González-Elizondo et al. 2005, López-Martínez et al. 2008, Pérez-López et al. 2009).
Preliminary checklists of Cyperaceae for Mexico include those of Espejo-Serna & López-Ferrari (1997), Diego-Pérez & González-Elizondo (2009) and Villaseñor (2016), but no conspectus of the family has been made for Mexico. An updating of the taxonomy and nomenclature of Mexican sedges is required to reflect recent taxonomic rearrangements in many genera as well as additions and exclusions of names for the Mexican flora. We present a checklist of the Cyperaceae currently known for Mexico with comments on diversity, endemism and distribution by state, and we discuss the main gaps in the knowledge of the family for the country.
Materials and methods
A database of Mexican Cyperaceae was generated with basis in literature review, study of herbarium specimens and field work. Most of the references are cited in the text, mainly at the Background, Methods and Discussion sections. Field work, mainly focused on Carex, has been done from 1990 to date in the whole country with the exception of the states of Guerrero, Quintana Roo, Tlaxcala and Yucatan. Herbaria reviewed from Mexico and elsewhere include CIIDIR, ENCB, GBH, HCIB, IBUG, IEB, INEGI, MICH, MEXU, QMEX, and SLPM (herbarium acronyms according to Thiers, continuously updated). Refining of the database involved nomenclatural updating, detection of synonyms, review of doubtful names and exclusion from the Mexican flora of names of taxa whose presence in the country has not been corroborated. The classification at the subfamily and tribe levels follows Muasya et al. (2009a, b) and the circumscription of genera follows Dorr (2014), Larridon et al. (2011, 2013, 2014), Bauters et al. (2014), and The Global Carex Group (2015, 2016). To verify the names of species and authors, the web sites Tropicos (http://www.tropicos.org) and The International Plant Names Index (http://www.ipni.org) were used.
From the dataset obtained, we calculated diversity, distribution by state and endemism level. Those taxa with distribution restricted to the country are considered as endemic, whereas micro-endemic are those known from only a state. Endemicity to a zone known as Megamexico (Rzedowski 1991) was also considered. It slightly extends the ecological conditions of the country, including three regions: MM1 (Mexico and zones of the Sonoran and Chihuahuan deserts and Tamaulipan scrub that lie in southern United States), MM2 (Mexico and the area of Central America northern of the Nicaraguan depression) and MM3 (MM1 and MM2).
A comparison of the species richness among the Mexican states was made using absolute values, and also standardized values by applying Squeo et al. (1998) correction to soften the area effect: S/lnA (species number/natural logaritm of the state area in km2).
Results
Cyperaceae are represented in Mexico by 460 species and 20 varieties or subspecies (480 taxa) which belong to 21 genera in 10 of the 17 family tribes. The checklist of taxa with state distribution and endemism level is presented in the Appendix 1. The two subfamilies currently recognized are in the country, with Cyperoideae including almost 100 % of the species and Mapanioideae represented by only one species. The most diverse genera are Carex (138 species and varieties) and Cyperus (125), followed by Rhynchospora (65) and Eleocharis (57) (Table 1, Figure 1). The species previously treated under Uncina are at present recognized as Carex, whereas Kyllinga, Lipocarpha, Oxycaryum and Remirea are incuded in Cyperus. The main synonyms for those combinations are presented in Table 2.
Table 1 Cyperaceae in Mexico. Genera and number of species and subspecies/varieties by tribe and subfamily.
| Subfamilies | Tribes | Genera | Species | Subsp./Var. |
| Cyperoideae | Abildgaardieae | Abildgaardia | 2 | |
| Bulbostylis | 14 | |||
| Fimbristylis | 16 | |||
| Cariceae | Carex | 137 | 1 | |
| Cypereae | Cyperus | 113 | 12 | |
| Isolepis | 2 | |||
| Karinia | 1 | |||
| Eleocharideae | Eleocharis | 55 | 2 | |
| Fuireneae | Bolboschoenus | 2 | ||
| Fuirena | 7 | 2 | ||
| Schoenoplectiella | 2 | |||
| Schoenoplectus | 5 | |||
| Rhynchosporeae | Rhynchospora | 63 | 2 | |
| Schoeneae | Cladium | 1 | 1 | |
| Schoenus | 1 | |||
| Scirpeae | Amphiscirpus | 1 | ||
| Cypringlea | 3 | |||
| Scirpus | 4 | |||
| Sclerieae | Calyptrocarya | 1 | ||
| Scleria | 29 | |||
| Mapanioideae | Hypolytreae | Hypolytrum | 1 |
Table 2 Main synonyms under Carex and Cyperus proposed or confirmed in recent studies: 1. Bauters et al. (2014), 2. Dorr (2014), 3. Larridon et al. (2011), 4. Larridon et al. (2013), 5. Larridon et al. (2014), 6. The Global Carex Group (2015).
| Previous name | Accepted name | Source |
| Kyllinga brevifolia Rottb. | Cyperus brevifolius (Rottb.) Endl. ex Hassk. | 5 |
| Kyllinga odorata Vahl | Cyperus sesquiflorus (Torr.) Mattf. & Kük. | 5 |
| Kyllinga pumila Michx. | Cyperus hortensis (Salzm. ex Schltdl.) Dorr | 2, 5 |
| Lipocarpha mexicana Liebm. | Cyperus lipomexicanus Goetgh. | 1 |
| Lipocarpha micrantha (Vahl) G. C. Tucker | Cyperus subsquarrosus (Muhl.) Bauters | 1 |
| Lipocarpha microcephala (R. Br.) Kunth | Cyperus leptocarpus (F. Muell.) Bauters | 1 |
| Lipocarpha salzmanniana Steud. | Cyperus salzmannianus (Steud.) Bauters | 1 |
| Oxycaryum cubense (Poeppig et Kunth) Palla | Cyperus blepharoleptos Steud. | 3 |
| Remirea maritima Aubl. | Cyperus pedunculatus (R. Br.) J. Kern | 4 |
| Uncinia hamata (Sw.) C.B. Clarke | Carex hamata Sw. | 6 |
| Unicinia koyamae Gómez-Laur. | Carex koyamae (Gómez-Laur.) J.R.Starr. | 6 |
| Uncinia phleoides (Cav.) Pers. | Carex phleoides Cav. | 6 |
| Uncinia tenuis Poepp. ex Kunth | Carex firmula (Kük.) J.R. Starr | 6 |
At the state level, the highest richness was found in Chiapas (237 taxa, 52 % of the total) and Veracruz (206, 45 %), followed by Oaxaca (171, 37 %) and Jalisco (148, 32 %) (Figure 2, 3; Appendix 1). Two genera (Cypringlea and Karinia) and 111 species or infraspecific taxa are endemic to the country (24 %), 78 of them at a regional level, including 43 micro-endemics. Endemism increases to 57 % when the biogeographic region known as Megamexico is included.
Discussion
The dataset of the Mexican sedge flora includes 460 species and 20 infraspecific taxa. Additionally, at least 45 undescribed species have been detected (not included in the checklist), which would increase to 525 the sedge taxa for the country. Suprageneric classification. The two subfamilies currently recognized (Cyperoideae and Mapanioideae) (Simpson et al. 2007, Muasya et al. 2009a) are in Mexico, although the predominantly tropical Mapanioideae is represented by only one species (Hypolytrum nicaraguense). As for the family tribes, 10 out of the 17 are in the country. The most diverse are Cariceae with 138 taxa and Cypereae with 128, whereas Hypolytreae is represented by one (Table 1). The Cariceae is a temperate group, mainly montane in Mexico, where represented by Carex (30 % of the taxa of this family). If compared with Madagascar, where the Cariceae are 11 % of the Cyperaceae (Muasya et al. 2011) or with Brazil (4.4 %, Alves et al. 2009), the group is fairly well represented in Mexico although still not quite as in any boreal zone, e.g., North America, where it composes 57 % of the sedge flora (Ball & Reznicek 2002). On the other hand, the tribe Cypereae, mainly tropical, includes 28 % of the sedge flora in Mexico, a high proportion when compared with North America (13 %) or even with Brazil (20 %), but low in relation with Madagascar, where the clade composes about half of the species in the family (Muasya et al. 2011).
Current circumscription of genera. The number of genera recognized in the present contribution is 21, which means a drastic reduction in comparison to previous inventories (27 genera recorded in Diego-Pérez & González-Elizondo 2009 following Bruhl 1995; 26 genera in the checklist of Villaseñor 2016). This is a result of recent phylogenetic findings and taxonomic rearrangements (Larridon et al. 2011, 2013, 2014, Bauters et al. 2014, the Global Carex Group 2015, 2016). According to these references, Uncinia is included into Carex, whereas Kyllinga, Lipocarpha, Oxycarium and Remirea are now part of Cyperus (Table 2), besides Pycreus and Torulinum, previously subsumed. On the contrary, several genera are split from what was previously considered as Scirpus s.l. (Lye 2003, Strong 2003). The possition of Abildgaardia is debatable. It is placed in Fimbristylis by some authors (e.g., Govaerts et al. 2015), but it has a significantly different embryology and anatomy (Kral 2002).
The relationships of the two genera endemic to the country still require study. Cypringlea is closely related to Trichophorum Pers. (Léveillé-Bourret et al. 2014) whereas Karinia is related to Scirpoides Scheuchz. ex Seguier (Goetghebeur 1998) and has been recently combined under it as Scirpoides mexicanus (Reznicek & McVaugh) Goetghebeur ex C.S. Reid & J.R. Carter (Reid et al. 2017). Ball et al. (2002) pointed out that no consensus exists regarding the number of genera in Cyperaceae; that is still true in part, although new approaches to their study are rapidly increasing our understanding on the family.
Distribution and ecology. The state distribution data are preliminary. The highest richness was found in Chiapas and Veracruz, followed by Oaxaca (Figure 2, 3). Jalisco, Michoacán, Tabasco, Durango and the state of Mexico form the next richest group. However, it is possible that Durango and the state of Mexico are not actually among the richest states but they have just a more complete inventory of sedges. The data of species richness standardized with the logarithm of the state surface area (Figure 3) corroborates that the higher diversity is located in Chiapas and Veracruz and reveals that the lower is in Baja California Sur and Tlaxcala. As already said, this may be related to the thoroughness of the inventories. However, the richness by state is strikingly similar to the obtained by Dávila-Aranda et al. (in rev.) for Mexican Poaceae, with Chiapas, Veracruz, Oaxaca and Jalisco as the most diverse (in the same order than for Cyperaceae), and Baja California Sur and Tlaxcala among the three less diverse states, also as with sedges. Although Oaxaca is ranked as the richest state of vascular plants in Mexico (Villaseñor 2016), with regard to grasses and sedges it holds the third position, behind Chiapas and Veracruz. This may be a result of under-representation of grasses and sedges from Oaxaca in herbaria and floristic lists and a better knowledge about them for Chiapas and Veracruz, or it may be explained for ecological reasons (e.g., perhaps the open habitats preferred by sedges and grasses are less available in Oaxaca). These ideas are beyond of the scope of the present work and demand future research.
Sedges in Mexico are found from sea level to above 4,300 m and grow practically in all types of land vegetation, from tropical forests to xerophytic scrub. Besides, a little more than a fourth of the Mexican sedges are aquatic or subaquatic (Diego-Pérez & González-Elizondo 2013), and many others, although not strictly aquatic, can be dominant in moist areas. However, other species can grow in dry areas in many types of vegetation. The wide variety of habitats that sedges can occupy explains in part the high diversity of this family in Mexico. Wetland loss and degradation, as well as overgrazing, are the main threats for many species of sedges (González-Elizondo & Tena-Flores 2017).
Endemism. Two genera (Cypringlea and Karinia) and 109 species (and two infraspecific taxa) are endemic to the country (24 %). A total of 78 of those endemic species display a very narrow geographical range; in fact, 43 are known from only a state (micro-endemics) and almost a half of them belong to Carex. The proportion of sedges endemic to the country is almost the same as the proportion of endemic grasses (22.5 %) reported by Dávila-Aranda et al. (in rev.), mirroring the striking similitude of the distribution by state of sedges and grasses above discussed. Although, the proportion of sedges with distribution restricted to a single state is slightly higher than for grasses (38.7 and 32.6 %, respectively).
Most of the species with a very restricted distribution are montane, e.g., Carex austromexicana, C. durangensis, C. evadens, Eleocharis cryptica, E. svensoniana. Environmental heterogeneity and niche diversity in montane habitats foster restricted distribution and speciation in many species, as also occurs in groups like Asteraceae or Salvia (Lamiaceae) (Villaseñor et al. 1998, González-Zamora et al. 2007, Cornejo-Tenorio & Ibarra-Manríquez 2011). Jiménez-Mejías et al. (2011) found that small ecological changes are drivers for speciation in a group of European Carex. But the main driver for fast speciation in small populations in sedges appears to be the chromosomal plasticity and differentiation via fission, fusion, and polyploidy favoured by the diffuse kinetochore that is typical of sedges (Luceño & Guerra 1996, Hipp et al. 2007).
Karinia mexicana, from the Mexican high plateau, is an example of regional endemism. Other species, although present in two or more states, have a restricted distribution, e.g., Carex eburnea in the Sierra Madre Oriental in Queretaro and San Luis Potosi; C. cochranei, C. hermannii and C. interjecta in small areas of the Neovolcanic Belt; another example is Cypringlea coahuilensis, confined to limestone ridges in desert habitats in Coahuila and Nuevo Leon.
Sedge endemism in Mexico (24 %) is lower than in Brazil (30 %, Alves et al. 2009) and Madagascar (37 % from out 321 species, Muasya et al. 2011). On the other hand, there are no genera endemic to Brazil and only one is endemic to Madagascar. As a no insular country, Mexico shares a high proportion of its flora with neighbor countries. Nevertheless, endemism increases remarkably when the biogeographic region known as Megamexico (MM) (Rzedowski 1991) is considered (for a description see Methods section). As for Cyperaceae, 57 % of the species are endemic to this region, which represents more than two-fold the ammount of sedges restricted to the political limits of the country. Some (e.g., Bulbostylis schaffneri, Carex bella, C. muriculata) are known from southwestern United States of America to northern or central Mexico (MM1); others, as Carex koyamae and E. yecorensis, are distributed from Mexico to Nicaragua (MM2); and a third group (e.g., Carex geophila, C. planostachys) distribute from southern United States of America to Central America (MM3). Another kind of regional endemics are those restricted to the Californian region, e.g., Carex globosa and C. triquetra, the first from moist places with conifers and the second from dry grasslands and scrub (Ball & Reznicek 2002).
Excluded names for the Mexican flora. About 46 names are excluded from the Mexican flora. Among them are Bulbostylis juncoides (Vahl) Kük. ex Osten, and Carex brehmeri Boeckeler, whose distribution is restricted to South America, as well as Bolboschoenus fluviatilis (Torr.) Soják, Carex atrata L., Carex aurea Nutt., Carex densa (L.H. Bailey) L.H. Bailey, C. leporina L., and C. leptopoda Mack., which are known from North America or are Holarctic in distribution, but not known to reach Mexico.
Bulbostylis hirta (Thunb.) Svenson is a synonym of Fimbristylis squarrosa Vahl, a pantropical species whose presence in Mexico has not been confirmed; the Mexican and North American plants to which the name B. hirta has been misapplied shall be called Bulbostylis hispidula (Lye 2006). Lipocarpha humboldtiana Nees (= Cyperus sellowianus (Kunth) T. Koyama) is known from Honduras to South America, and Lipocarpha maculata (Michaux) Torrey (= Cyperus neotropicalis Alain), from eastern North America (Washington, D.C. to Florida). Lipocarpha mexicana (= Cyperus lipomexicanus Goetgh.) is considered as a synonym of L. maculata in recent catalogs but is recognized as an independent species in a revision of the group (Bauters et al. 2014).
Given that many previously cited names correspond to synonyms and 46 names are excluded here, the current number of recognized species (460) is lower than the 489 listed by CONABIO (Diego-Pérez & González Elizondo 2009), although higher than the 416 species included in the checklist of Villaseñor (2016).
Some gaps in the knowledge of Mexican Cyperaceae. The cytology of a few species has been studied in Eleocharis (Tena-Flores et al. 2013) and Schoenoplectus (Tena-Flores et al. 2014) and Mexican species have been included in several molecular studies elsewhere. Nevertheless, many of the endemic species have not been cytogenetically or molecularly analyzed.
Collection deficiencies and insufficient taxonomic revision for Mexican sedges are reflected in gaps in their knowledge. It is very probable that species that are widely distributed may be in Mexico but have not yet been discovered in its territory. For example, Eleocharis confervoides (Poir.) Steud. is known from southeastern United States and eastern Central America and may be in coastal areas of Campeche and Yucatan. Some Cyperus are cited by Tucker (1994) as of probable presence in Mexico given that they are known from localities close to the Mexican border: Cyperus hayesii (C.B. Clarke) Standley from the Pacific coast from Guatemala to Colombia, and C. setigerus Torr. & Hook. and C. strigosus L. from the United States of America reaching San Diego County and the Rio Grande plains, respectively.
Many complexes of species are in need of taxonomic revision. The main gaps in taxonomic knowledge are in Carex, as noted also elsewhere by Reznicek (1989), The Global Carex Group (2015), Jiménez-Mejías et al. 2016, among others. However, many problems remain to be solved also in Bulbostylis, Cyperus, Eleocharis, Rhynchospora and Scleria. Additional to the 460 species recorded for the country, there are at least 45 undescribed species. With them, the net richness of Mexican sedges is of about 505 species plus 20 infraspecific taxa.
Therefore, regardless of the addition of taxa and refinement of the database of sedges for Mexico, the checklist presented here is still preliminary. There is still much basic work to be done before Mexican Cyperaceae are well understood.
