Variation in Pollen Tube Inhibition Sites Within and Among Three Heterostylous Species of Rubiaceae

Abstract

Pollen tube growth was examined following self, intramorph, and intermorph pollinations in three distylous species of Rubiaceae, the angiosperm family containing the greatest number of distylous taxa. Hand pollinations of Psychotria poeppigiana Muell. Arg., Psychotria chiapensis Standl., and Bouvardia ternifolia (Cav.) Schlecht. were followed by observation of pollen tube growth using fluorescence microscopy. Patterns of pollen tube growth were compared between conspecific floral morphologies, among type of illegitimate pollination, and among taxa. Short‐styled flowers of both Psychotria L. species had a majority of illegitimate pollen tube growth arrested within the stigma. In long‐styled Psychotria L. flowers, illegitimate pollen tube growth was inhibited either within the stigma or at various locations within the style. In the more distantly related B. ternifolia (Cav.) Schlecht., variable inhibition sites ranged from the stigma surface to the base of the style, among both short‐ and long‐styled flower...