Morpho anatomical and morphometric studies of the floral structures of the distylous oldenlandia salzmannii (rubiaceae)

Abstract

The genus Oldenlandia (Rubiaceae) has a conflicting generic delimitation, with representatives that show diff erent floral syndromes. Oldenlandia salzmannii is a marshy herb that is widespread in South America. It is heterostylous, specifi cally distylous, and self-compatible. Recent molecular phylogenetic studies found that this species forms a clade that is isolated from the remaining described taxa of Oldenlandia. Information about the floral anatomy and reproductive biology of genera in the Spermacoceae tribe, particularly Oldenlandia, is insuffi cient, especially among the neotropical species. Accordingly, the present study aimed at contributing information on the reproductive biology of Oldenlandia salzmannii by analyzing its floral morpho-anatomy, morphometrics and phenology of both floral morphs. These analyses were conducted with natural, cultivated and fi xed material using optical and scanning electron microscopes. Morphologically, the species is typically heterostylous with two fl oral morphs, long-styled and short-styled, the main diff erence being the indument of the corolla. Th e short-styled fl owers have larger anthers and pollen grains. Morphometrics show a high degree of herkogamic reciprocity. Th e mature ovules have a hemitropous position, which is the fi rst record of this position for the Spermacoceae tribe. This study represents the fi rst comprehensive morphological study of Oldenlandia salzmannii.