THE HEDYOTIS–OLDENLANDIA–KOHAUTIA COMPLEX (RUBIACEAE) IN NEPAL: A STUDY OF FRUIT, SEED AND POLLEN CHARACTERS AND THEIR TAXONOMIC SIGNIFICANCE

Abstract

Pollen and seed characters of 12 Nepalese representatives of the Hedyotis–Oldenlandia–Kohautia complex (Spermacoceae s.l.; Rubiaceae) were investigated morphologically using scanning electron and light microscopy. The members of the complex were found to show remarkable variation in fruit, seed and pollen features. Pollen grains were all colporate with the aperture number varying from 3–4 to occasionally 5. The ectoaperture was a colpus, and the endoaperture was an endocingulum, a lalongate endocolpus or an endocolpus combined with an annulus around the mesoporus. Sexine ornamentation was variable, being perforate, reticulate or microreticulate. Three species were found to have a double reticulum. Supratectal elements were generally absent, but sometimes muri were beset with granules. Seeds were numerous per capsule, small and non-crateriform. Three types of seed were distinguished based on shape: (1) lenticular with a narrow wing-like margin, (2) trigonous, and (3) globose/subglobose. Trigonous seeds exhibited marked variation in colour, size and shape. On the basis of the pollen and seed characters, used in combination with the type of fruit dehiscence, five natural groups are identified for Nepalese taxa. The generic status of Hedyotis, Oldenlandia and Kohautia is maintained but some species are transferred from Hedyotis to Oldenlandia. Pollen and seed morphology, together with the type of fruit dehiscence, proved to be helpful in delimiting supra- and infrageneric groups within the Hedyotis–Oldenlandia–Kohautia complex.