Distyly and Population Structure of Neanotis montholonii (Hook F.) W.H. (Rubiaceae)

Distyly in Neanotis monthlonii (Hook F.) W.H. (Rubiaceae) is described for the time. The heterostyly with Pin and thrum forms is described and the natural populations studied show balanced polymorphism, hence isopleths. Distyly is reciprocal mechanical arrangement of style and stamen height accompanied by an array of contrasting differences in pollen and stigma papillae features accompanied by physiological incompatibility. The pin and thrum morphs are self incompatible but cross compatible. Based on the data available it is suggested that the S supergene controls the genetic architecture in the species.