With more than 500 species, Mimosa L. is one of the largest genera of the Leguminosae. It exhibits considerable trichome diversity among species. Trichome types have been used as diagnostic characters, but some are not well known and have been poorly described in taxonomic works, causing some difficulties for species identification and description. The morphology of trichomes of 35 species was studied using scanning electron microscopy and light microscopy to define the types of trichomes precisely. An ancestral character state reconstruction using a densely-sampled phylogeny of the genus was performed in order to investigate the evolution of trichome types in Mimosa. Two basic types of trichomes can be distinguished: glandular and non-glandular. The glandular trichomes can be sessile or stalked. The non-glandular trichomes can be unbranched or branched. Unbranched trichomes are unicellular and conical or cylindrical, whereas branched trichomes are multicellular and verruciform, medusiform, plumose, barbellate, stellate, stellate-lepidote, or lepidote. Character optimization analysis suggests that glandular and branched trichomes are derived and evolved independently in different lineages within Mimosa. The ancestral condition in Mimosa was probably non-glandular and unbranched trichomes, which was retained from piptadenioid ancestors. Our study provides a first insight into the evolutionary history of trichome morphology in the genus. Despite high levels of homoplasy, trichome morphology offers a set of characters that can be used for differentiating species and species groups in combination with other characters.

Early natural historians—Comte de Buffon, von Humboldt, and De Candolle—established environment and geography as two principal axes determining the distribution of groups of organisms, laying the foundations for biogeography over the subsequent 200 years, yet the relative importance of these two axes remains unresolved. Leveraging phylogenomic and global species distribution data for Mimosoid legumes, a pantropical plant clade of c. 3500 species, we show that the water availability gradient from deserts to rain forests dictates turnover of lineages within continents across the tropics. We demonstrate that 95% of speciation occurs within a precipitation niche, showing profound phylogenetic niche conservatism, and that lineage turnover boundaries coincide with isohyets of precipitation. We reveal similar patterns on different continents, implying that evolution and dispersal follow universal processes.

Here we describe the morphological variability, chromosome number, and chromosome size in Mimosa diversipila. This species comprises two varieties, which are distinguished by the indumentum. However, this character is insufficient for circumscription of these infraspecific taxa. Using multivariate techniques, we found that quantitative characters were useful for identification of the varieties, which also have a different geographic distribution. Cytogenetic studies revealed that these taxa form a polyploid complex and that the polyploidy may contribute to the morphological variability observed.