The floral structure of three weedy species of Sida (Malvaceae)

Abstract

Malvaceae sensu lato is monophyletic and is characterized by the presence of nectaries of glandular trichomes, located internally at the base of the calyx. The genus Sida has been heterogeneous since its origin; however, there has been a reduction in the size of the genus with the removal of many species to other genera, giving a more natural and definable residual group subdivided into 11 sections. The aims of this work were to describe and compare the floral structure of three weedy species Sida rhombifolia, S. urens, and S. regnellii, using a traditional anatomical approach, along with scanning electron microscopy analysis. The comparative study of the three Sida species allows us to suggest that some structural characters are shared, i.e., the hypodermis in the sepal and ovary wall, trichomatous calyx nectary, perianth with homogeneous mesophyll, and anther with a middle layer and plasmodial tapetum type, and they may reinforce the natural residual group of Sida. On the other hand, other floral characters have some diagnostic value for classification at the species level, such as the style structure being solid or rift in the center.