Oxalis sect. Palmatifoliae (Oxalidaceae): pollen grains morphology and orbicules diversity

Pollen morphology and orbicules characteristics were studied by means of transmitted light microscopy (LM) and scanning electron microscopy (SEM) within five species of Oxalis section Palmatifoliae endemic from southern South America. Oxalis pollen grain is generally 3-colpate and the shape is prolate spheroidal, oblate spheroidal or spheroidal. The exine is microreticulate. The brochi are circular to polygonal; brochi decrease in size near the colpi. The orbicules are randomly dispersed on the inner surface of the anther locule. They are mostly plate-like, rounded shape, or doughnut, with smooth surface. The homogeneity observed in the pollen grains of all species of Oxalis section Palmatifoliae may reinforce the hypothesis of the monophyletic origin of the group, and the variability in orbicles types may contribute to the interspecific differentiation.