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Revision of Poa L. (Poaceae, Pooideae, Poeae, Poinae) in Mexico: new records, re-evaluation of P. ruprechtii, and two new species, P. palmeri and P. wendtii.

ABSTRACT: A revision and key to the 23 species and eight subspecies of Poa (including Dissanthelium) known to occur in Mexico is provided. All voucher specimens seen are cited for accepted taxa, except Poa annua for which one voucher per state is provided. Taxa not previously known from, or poorly understood in, Mexico are discussed.Poa palmerisp. nov. is endemic to forested slopes of the Sierra Madre Oriental, and we distinguished it from Poa ruprechtii s.s., a species of central Mexico that is here emended to include Poa sharpii (syn. nov.). Poa wendtiisp. nov. is described from the Sierra Santa Rosa in northern Coahuila. Poa tacanae is placed in synonymy in Poa seleri. Poa gymnantha and Poa occidentalis are newly reported for Mexico, and material historically identified as Poa villaroelii areplaced in Poa chamaeclinos.The genus Dissanthelium is considered to belong within Poa, and the Mexican taxa, Dissanthelium calycina subsp. mathewsii and Dissanthelium californicum, are treated as Poa calycina var. mathewsii and Poa thomasii, respectively. Poa subsect. Papillopoasubsect. nov. is erected for Poa mulleri. Lectotypes are designated for Poa conglomerata and Poa seleri.

SUBMITTER: Soreng RJ

PROVIDER: S-EPMC3492929 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Background and aimsPoa subgenus Poa supersect. Homalopoa has diversified extensively in the Americas. Over half of the species in the supersection are diclinous; most of these are from the New World, while a few are from South-East Asia. Diclinism in Homalopoa can be divided into three main types: gynomonoecism, gynodioecism and dioecism. Here the sampling of species of New World Homalopoa is expanded to date its origin and diversification in North and South America and examine the evolution and origin of the breeding system diversity.MethodsA total of 124 specimens were included in the matrix, of which 89 are species of Poa supersect. Homalopoa sections Acutifoliae, Anthochloa, Brizoides, Dasypoa, Dioicopoa, Dissanthelium, Homalopoa sensu lato (s.l.), Madropoa and Tovarochloa, and the informal Punapoa group. Bayesian and parsimony analyses were conducted on the data sets based on four markers: the nuclear ribosomal internal tanscribed spacer (ITS) and external transcribed spacer (ETS), and plastid trnT-L and trnL-F. Dating analyses were performed on a reduced Poa matrix and enlarged Poaceae outgroup to utilize fossils as calibration points. A relaxed Bayesian molecular clock method was used.Key resultsHermaphroditism appears to be pleisiomorphic in the monophyletic Poa supersect. Homalopoa, which is suggested to have originated in Eurasia 8·4-4·2 million years ago (Mya). The ancestor of Poa supersect. Homalopoa radiated throughout the New World in the Late Miocene-Early Pliocene, with major lineages originating during the Pliocene to Pleistocene (5-2 Mya). Breeding systems are linked to geographic areas, showing an evolutionary pattern associated with different habitats. At least three major pathways from hermaphroditism to diclinism are inferred in New World Homalopoa: two leading to dioecism, one via gynodioecism in South America and another directly from hermaphroditism in North America, a result that needs to be checked with a broader sampling of diclinous species in North America. A third pathway leads from hermaphroditism to gynomonoecism in Andean species of South America, with strictly pistillate species evolving in the highest altitudes.ConclusionsDivergence dating provides a temporal context to the evolution of breeding systems in New World Poa supersect. Homalopoa The results are consistent with the infrageneric classification in part; monophyletic sections are confirmed, it is proposed to reclassify species of sect. Acutifoliae, Dasypoa and Homalopoa s.l. and it is acknowledged that revision of the infrageneric taxonomy of the gynomonoecious species is needed.

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Revision of Poa L. (Poaceae, Pooideae, Poeae, Poinae) in Mexico: new records, re-evaluation of P. ruprechtii, and two new species, P. palmeri and P. wendtii.

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