Brittonia最新文献

Dalea verticillata is described and illustrated as a new species from Oaxaca, Mexico. Dalea verticillata is similar to D. filiciformis, but it is distinguished by having whorled leaves (vs. alternate in D. filiciformis), with a greater number of leaflets ((31–)39–63(–69) vs. (11–)13–29(–37)), longer stipules (4.5–8 mm vs. 0.3–1.5 mm), reflexed (vs. ascending), persistent (vs. deciduous), terminal panicle inflorescences (vs. axillary racemes), and the wing petals subelliptic (vs. ovate). This is the second species of the hitherto monospecific subgenus Psoropteris, and the whorled-leaf character is recorded for the first time in the genus Dalea.

Grias lucindoae, a new species from the Western Andean slopes of the Eastern Cordillera of Colombia (Serranía de Las Quinchas), is described and illustrated, and its morphological similarities with comparable species are discussed. This new species is a tree between 10 and 15 m tall from montane forest remnants (900–1200 m). Grias lucindoae shares several features with G. angustipetala and G. cauliflora. It differs in the size and pubescence of the leaf blade, pedicels, the number of secondary veins and stamens, calyx dehiscence, size, shape, and color of the petals, and the 4-lobed stigma, which is truncated when mature. Additionally, a table comparing morphological characters of G. lucindoae to the other Grias species that occur in Colombia is presented, as well as an identification key of the Neotropical species. With this new species, there are now nine species of Grias in the flora of Colombia, which, along with Ecuador, are countries with the highest diversity of the genus.

The X chromosome, being hemizygous in males, is exposed one third of the time increasing the visibility of new mutations to natural selection, potentially leading to different evolutionary dynamics than autosomes. Recently, we found an enrichment of hard selective sweeps over soft selective sweeps on the X chromosome relative to the autosomes in a North American population of Drosophila melanogaster. To understand whether this enrichment is a universal feature of evolution on the X chromosome, we analyze diversity patterns across six commonly studied Drosophila species. We find an increased proportion of regions with steep reductions in diversity and elevated homozygosity on the X chromosome compared to autosomes. To assess if these signatures are consistent with positive selection, we simulate a wide variety of evolutionary scenarios spanning variations in demography, mutation rate, recombination rate, background selection, hard sweeps, and soft sweeps, and find that the diversity patterns observed on the X are most consistent with hard sweeps. Our findings highlight the importance of sex chromosomes in driving evolutionary processes and suggest that hard sweeps have played a significant role in shaping diversity patterns on the X chromosome across multiple Drosophila species.

A new lithophytic species of Gesneria was discovered during a recent research expedition to the Dominican Republic. Gesneria clasei J.L.Clark is a locally endemic species known from a single population in the Sierra de Bahoruco in the southwestern province of Barahona in the Dominican Republic. Images and a discussion are provided to differentiate Gesneria clasei from congeners that share tubular red corollas. Based on IUCN guidelines, a preliminary conservation status of Critically Endangered (CR) is assigned to G. clasei.