title: Phylogenetic analyses and morphological characteristics support the description of a second species ofTridimeris(Annonaceae).
abstract: Based on phylogenetic and morphological evidence,Tridimeris chiapensisEscobar-Castellanos & Ortiz-Rodr.,sp.n.(Annonaceae), a new species from the karst forest of southern Mexico, is described and illustrated. The new species differs fromTridimeris hahniana, the only described species in the genus, in that the latter has flowers with sepals densely tomentose outside, one (rarely two) carpel(s) per flower and fruits densely covered with golden-brown hairs, whileTridimeris chiapensishas flowers with glabrous sepals outside, two to five carpels per flower and glabrous fruits. Furthermore, a shallow triangular white patch at the base of the inner petals is found inTridimeris chiapensis, a morphological character shared with the sister genusSapranthusbut absent inTridimeris hahniana. Geographically, both species occur allopatrically. With just one known locality and seven individuals ofTridimeris chiapensisrecorded in one sampling hectare, and based on application of the criteria established by the IUCN, we conclude tentatively that the species is critically endangered.
authors.affiliation: Departamento de Biologia Evolutiva, Instituto de Ecologia A.C., Xalapa, Veracruz, Mexico.
authors.forename: Andres Ernesto
authors.initials: AE
authors.lastname: Ortiz-Rodriguez
authors.affiliation: Instituto de Ciencias Biológicas, Universidad de Ciencias y Artes de Chiapas, Tuxtla Gutierrez, Chiapas, Mexico.
authors.forename: Marcos Alberto
authors.initials: MA
authors.lastname: Escobar-Castellanos
authors.affiliation: Instituto de Ciencias Biológicas, Universidad de Ciencias y Artes de Chiapas, Tuxtla Gutierrez, Chiapas, Mexico.
authors.forename: Miguel Angel
authors.initials: MA
authors.lastname: Pérez-Farrera
keywords: Dimery; Miliuseae; Neotropical; tropical rainforest