Rosa Cerros-Tlatilpa

C3 photosynthesis in Aristida longifolia: Implication for photosynthetic diversification in Aristidoideae (Poaceae).

Only a small percentage of plant species undergo C(4) photosynthesis. Despite its rarity, the C(4) pathway has evolved numerous times from C(3) ancestors, with as many as 18 independent origins in grasses alone. We report non-Kranz (C(3)) anatomy in Aristida longifolia, a species in a genus of ca. 300 species previously thought to possess only Kranz (C(4)) anatomy. Leaf blade transections of A. longifolia show widely spaced vascular bundles, nonradiate chlorenchyma, and few or no chloroplasts in cells of the sheaths surrounding the vascular bundle, all features indicative of C(3) photosynthesis. Carbon isotope ratios range from -27.68 to -29.71%, likewise indicative of C(3) photosynthesis. We also reconstruct the phylogeny of Aristidoideae, comprising Aristida, Sartidia (C(3)), and Stipagrostis (C(4)), using a sample of 11 species, including A. longifolia, and DNA sequences of the nuclear ribosomal internal transcribed spacer region and the chloroplast rpl16 intron and trnL-trnF region. Sartidia and Stipagrostis resolve as sisters, and sister to this clade is Aristida. Aristida longifolia resolves as sister to the remaining species in the genus. C(3) photosynthesis is hypothesized to be ancestral in Aristidoideae, which means the C(4) pathway evolved twice in the subfamily-in Stipagrostis and early in the diversification of the Aristida clade.

Phylogenetic relationships of Aristida and relatives (Poaceae, Aristidoideae) based on noncoding chloroplast (trnL-F, rpl16) and nuclear (ITS) DNA sequences.

PREMISE The cosmopolitan and ecologically important grass subfamily Aristidoideae comprises the widely distributed genus Aristida (250-290 species), Stipagrostis (50 species, with an African-Asian distribution), and Sartidia (five species, Africa and Madagascar). The subfamily includes species with C(3) (Sartidia and a single species of Aristida) and C(4) photosynthetic pathways. Rigorous phylogenetic reconstructions of species relationships are required to explain the biogeographic, physiological, and ecological diversity within this subfamily. METHODS Chloroplast (trnL-F, rpl16) and nuclear (ITS) DNA sequences were obtained from 198 accessions, and the combined data set was subjected to parsimony, maximum likelihood, and Bayesian inference analyses. Dating analyses calibrated using previously published node ages were conducted to determine the ages of major radiations. RESULTS The C(3) Sartidia is sister to a monophyletic Stipagrostis, and the (Sartidia, Stipagrostis) clade is sister to Aristida. Within Aristida, the only known C(3) species, A. longifolia, is sister to the remainder of the genus. Infrageneric sections of Aristida were not supported, and there are no synapomorphic morphological characters for the clades retrieved. Within Aristida, monophyletic Australian, African, North American, and South American clades are retrieved. CONCLUSIONS The subfamily dates back to the late Miocene, with the major lineages present by the Pliocene. With one exception, regional clades of Aristida evolved in the Pliocene. The C(3) photosynthetic pathway is hypothesized to be the pleisomorphic condition for the subfamily, wherein two independent C(4) pathways (each with unique anatomical and genetic features) evolved, one within Aristida and one in Stipagrostis.

A New Species of Amyris (Rutaceae) from Durango, Mexico

Abstract Amyris roseomaculata, a new species from the state of Durango, Mexico, is described and illustrated. The new species is morphologically similar to A. rekoi Blake because both have 5-merous flowers, unifoliolate leaves, and leaflets and petioles are similar in length. However, A. roseomaculata is differentiated from that species due to the shape of calyx lobes and nectary disc, and the ovary clearly differentiated from the nectary disc. In addition, A. roseomaculata is known only from Durango, Mexico, while A. rekoi is distributed only in the state of Oaxaca. A comparative table is included as well as images and a distribution map of the two species.

New records of flowering plants in Morelos state, Mexico

Nine new records of flowering plants are reported for Morelos state, Mexico. Most of the species occur at the Biological Corridor Chichinautzin and the Biosphere Reserve Sierra of Huautla, located at north and south of Morelos state, respectively. A brief diagnosis, phenology, notes and illustrations are included. These records are the outcome of floristic studies carried out by the authors in both natural reserves.