Stem trichome morphology in Mimosa L. (Fabaceae – Mimosoideae) with potential taxonomic significance

Mimosa L. (Fabaceae) is the second largest genus within of Mimosoideae clade, with predominantly neotropical distribution. The plant indumentum and the degree of pubescence have in many cases been successfully applied to the taxonomy of different taxa. The aim of this paper was to analyze the trichomes of the stem and axis inflorescence of 14 species of Mimosa, which may constitute useful taxonomic characters within genus. The samples were collected in the upper river Paraná floodplain, western region of the state of Parana, Brazil, and they were investigated under light microscope and scanning electron microscopy (SEM). Most of the investigated species consist of non-branched non-glandular trichomes on the stem and inflorescence axis, of the subtypes conical, cylindrical and flat, but the other trichome types were found, as the branched non-glandular trichomes, subtypes plumose and barbellate. The stalked and clavate glandular trichomes are especially striking in some species. Mimosa somnians is devoid of trichomes. The segregation of the 14 species and a variety studied of Mimosa is fully supported by evidence from trichome morphology associated to the characters of wall ornamentation, density and length of the trichomes.