The distribution and systematic significance of pollen nuclear number in the Rubiaceae.

Abstract

Data on the distribution of binuclaeate and trinucleate pollen grains in 103 species representing 32 genera and 15 tribes of the Rubiaceae from South India are reported. In general, the pollen nuclear number showed remarkable constancy within individual tribes and genera except the tribe Hedyotideae and the genus Oldenlandia.In great bulk of the species the vegetative nucleus underwent degeneration during the course of microspore development. Pollen nuclear number showed recognisable relationship with pollen aperture number, the binucleate species posses-sing 3-aperturate grains and trinucleate ones six or more aperturate grains. The pollen nuclear number also showed an association with growth habit, the trinucle-ate condition being present exclusively in herbaceous genera. These associations appear to be suggestive of a non-random distribution of the two nuclear types in the family.The systematic significance of pollen nuclear number in the family is discussed, supplemented with evidences from chromosomal and palynological data. As regards the delimitation and systematic position of various tribes, Bremekamp's classification is shown to be by and large in agreement with the cytological and palynological data. Affinities of the Rubiaceae with other families are examined in the light of the present data, and it is shown that the Gentianalean affinity is more natural.