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An assessment of the extinction risk of the endemic plants from the Yucatán Peninsula Biotic Province (YPBP) was performed based on distributional data (B criteria of the IUCN) using the GeoCAT tool. The YPBP is located in southeastern Mexico and comprises the Mexican states of Campeche, Quintana Roo, and Yucatán, and the northernmost portion of Belize (districts of Belize, Corozal, and Orange Walk), as well as a portion of northern Guatemala (most of the department of Petén). An analysis of the YPBP flora identified 167 endemic taxa, 154 of which grow in at least one of the three Mexican states (Campeche, Quintana Roo, and/or Yucatán), whereas another 13 occur exclusively in Belize and/or Guatemala. Eighty-five are in some category of risk (50.9%): 17 taxa (10.18%) are categorized as Critically Endangered (CR), 40 (23.95%) as Endangered (EN), and 28 (16.77%) as Vulnerable (VU). Eighty-one (48.5%) species are not threatened: 12 (7.19%) as Near Threatened (NT) and 69 (41.32%) as Least Concern. A single species (0.6%) is considered Data Deficient (DD). The greatest number of endemic species and endemic threatened species inhabit dry and subhumid forests, and some inhabit semi-evergreen forests. The habits of endemic species and threatened endemic species are diverse, but trees, grasses, and shrubs predominate. The official system of protected natural areas (PNA) does not guarantee the conservation of all endemic species in the region. Ninety-eight (58.68%) of the endemic taxa have more than one population (record) within a PNA.

We present the most complete molecular phylogeny to date of the Pithecellobium clade of subfamily Caesalpinioideae. This neotropical group was informally recognised (as the Pithecellobium alliance) at the end of the 20th century by Barneby and Grimes (1996) and includes five genera and 33 species distributed from the southern United States and Caribbean Islands to north-eastern South America. Our aims were to further test the monophyly of the group and its genera and to identify sister group relationships within and amongst the genera. A phylogenetic analysis of nuclear ribosomal DNA sequences (ITS and ETS) was performed. The results provide further support for the monophyly of the Pithecellobium clade. The genera Ebenopsis, Pithecellobium and Sphinga were strongly supported as monophyletic. Havardia and Painteria were found to be non-monophyletic, prompting their re-circumscriptions and the description of two new genera: Gretheria and Ricoa. New combinations are made for the three species transferred to the new genera.

Antecedentes y Objetivos: Lysiloma es un género neotropical de la familia Fabaceae que comprende ocho especies, seis de las cuales se distribuyen ampliamente en México y dos más que ocurren en las Antillas y La Florida. Lysiloma es frecuente en los bosques secos de Megaméxico. Un estudio filogenético previo incluyó tres especies de Lysiloma y Hesperalbizia occidentalis. Ambos géneros están estrechamente relacionados, pero su divergencia tiene un apoyo débil. Nuestros objetivos fueron probar la monofilia del género, evaluar las relaciones de grupo hermano dentro del género y estimar los tiempos de divergencia. Métodos: Se realizó un análisis filogenético basado en caracteres morfológicos, marcadores moleculares (ETS, matK y trnK), así como un análisis combinado (morfología + moléculas). Las matrices de datos se analizaron tanto individualmente como concatenadas (enfoque de evidencia total) con inferencia Bayesiana y máxima parsimonia. Además, los tiempos de divergencia molecular se estimaron a partir del conjunto de datos ETS con un modelo de reloj bayesiano relajado lognormal no correlacionado. Resultados clave: El análisis morfológico respalda la monofilia del Lysiloma con Hesperalbizia como grupo hermano. Sin embargo, los análisis moleculares individuales y combinado no proporcionan resolución para aclarar las relaciones entre Hesperalbizia occidentalis, Lysiloma sabicu y el núcleo de Lysiloma. El análisis de evidencia total (incluida la morfología) respalda la monofilia de Lysiloma, pero con un bajo soporte. Según nuestro modelo de reloj molecular, el clado Lysiloma+Hesperalbizia se separó de otros miembros de la tribu Acacieae+Ingeae hace unos 32 millones de años y la diversificación del núcleo del Lysiloma se produjo a lo largo del Mioceno.Conclusiones: Lysiloma+Hesperalbizia es un clado de divergencia temprana de las tribus Acacieae+Ingeae. Existen suficientes diferencias morfológicas para reconocer ambos linajes. Los caracteres morfológicos utilizados informalmente para la delimitación taxonómica parecen haber evolucionado de manera homoplásica. El clado de Lysiloma y Hesperalbizia se separó de otros miembros de la tribu Acacieae+Ingeae en el Oligoceno, pero la diversificación del núcleo del género coincidió con la expansión del bosque seco a principios del Mioceno.

A new combination, Coursetia greenmanii (Leguminosae, Papilinioideae, tribe Robinieae), is proposed because analysis of nucleotide sequence data from the nuclear ribosomal internal transcribed spacer region resolves a clade that is phenotypically distinct and ecologically and geographically centered in lowland seasonally dry tropical vegetation of the Yucatan Peninsula region. The well supported monophyly of the ribosomal sequences sampled from Coursetia greenmanii suggests that this species has had a long history independent of its close relatives. Coalescence of intraspecific samples of ribosomal sequences from this geographically confined species is strongly suggestive of an evolutionary persistent small effective population size. This is the general case for species of Coursetia and related genera of the tribe Robinieae. Coalescence of nuclear ribosomal sequences sampled from geographically restricted species in this group further suggests that evolutionary persistence could be the result of high levels of dispersal limitation in seasonally dry Neotropical vegetation that is rich in cacti and other succulent species. This is the ecological setting to which Robinieae shows phylogenetic niche conservatism.

In the Mexican portion of the Yucatan Peninsula there are three species of Zygia (Leguminosae, Mimosoideae, Ingeae). Their morphological differences and nomenclature are discussed. A key, descriptions, iconography, ecological, phenological, uses and common names are included. En la porción mexicana de la Península de Yucatán hay tres especies del género Zygia (Leguminosae, Mimosoideae, Ingeae). Se discuten sus diferencias morfológicas y nombres correctos. Se incluye una clave, descripciones, iconografía, información ecológica, fenológica, nombres comunes y usos.

Capraria mexicana Moric. ex Benth. es reportada por primera vez para la porción mexicana de la Provincia Biótica Península de Yucatán. Además, se realizan comentarios generales sobre el género Capraria y se incluye una clave para identificar las tres especies que crecen en la región.