Sex expression in Canthium mundianum (Rubiaceae)

Abstract

While investigating the validity of the segregation of Canthium gilfillanii (N.E. Br.) O.B. Miller from Canthium mundianum Cham. & Schlechtd., we noticed that flowers in a population were of different sizes and either female or hermaphrodite. Preliminary conclusions of the former study, suggest that C. gilfillanii and C. mundianum are indeed conspecific. The morphology of the style is specialised for pollen presentation in hermaphrodite flowers and for pollen reception in females. The anthers of hermaphrodite flowers contain copious viable pollen while those of female flowers are barren. The stigmatic area in both sexes is receptive, but enlarged in female flowers. All flowers on the same plant are of the same sex, throughout the flowering season and in successive seasons and the species is thus gynodioecious. Seed set was very successful in females, but very low in hermaphrodites, regardless of the amount of rainfall. Vegetative reproduction has led to the development of extensive clones.