Pollen morphological survey of Pentas (Rubiaceae-Rubioideae) and its closest allies

Pollen descriptions, based on LM and SEM observations, are provided for the Pentas complex, an African alliance within the Hedyotideae-Spermacoceae al liance, which includes the genera Pentas, Otomeria, Batopedina, Pauapentas, and Chamaepentas. The close relationship among these genera is confirmed b y pollen morphological data. The observed variation in pollen character sta tes agrees well with the existing genera and subgenera. The combination of small spheroidal pollen grains with narrow, acute endocolpi, and a small ap ocolpium index distinguishes Batopedina from Otomeria and Pentas. Parapenta s differs from Batopedina in having broad endocolpi with vague ends. Two of the three subgenera of Otomeria, Neotomeria and Volubilis, are suppo rted by pollen data. Pollen of the subgenus Otomeria, however, is less diff erentiated and is similar to pollen of Pentas subgenus Pentas. The exact re lationship between the genera Otomeria and Pentas remains unclear: and mole cular data are needed to interpret the observed morphological variation. Ch amaepentas has pollen that is nearly identical to that of the Pentas subgen us Chamaepentadoines and of the subgenus Megapentas, i.e, large spheroidal pollen grains with three, medium-length colpi and endocolpi with acute ends . Pollen morphology provides additional support for a close affinity betwee n Pentas subgenus Phyllopentas and Pentas subgenus Vignaldiopsis. (C) 2000 Elsevier Science B.V. All rights reserved.