Structure and behaviour of chromosomes in Piper and Peperomia (family Piperaceae)

Abstract

Fifty three taxa have been studied during the present investigation, including eight species of Piper and nine of Peperomia. In Piper chromosome numbers ranging from 2n=24 to 195 have been found and polyploidy has been shown to be an important factor in evolution. The species of Piper studied here have multiples of 13, except P. cubeba L.f. which is deep-seated for the genus. However in P. cubeba L.f. n=12 chromosomes may represent the basic set from which n=13 might have been derived and this number became deep-seated in the species of Piper, possibly due to selective advantage. All the species of Piper except P. cubeba L.f. show a gross uniformity in the karyotype. However, differences in the number of nucleolar chromosomes have been recorded.In Peperomia, eight taxa have shown 2n=22 chromosomes, whereas in P. nummularifolia H.B.K. and P. pellucida H.B.K. 2n=23 and 2n=44 chromosomes are seen respectively. In the genus Peperomia the basic set of n=11 chromosomes is pronounced. The karyotype is characterised by relatively larger chromosomes than that of the genus Piper. The species of Peperomia differ in minute details of karyotype, suggesting the role of minute structural alterations in evolution.Cytologically the two genera Peperomia and Piper are quite distinct from each other. These evidences taken in conjunction with the data obtained from anatomy, morphology, palynology, embryology and floral biology, support the separation of the two genera into two different families under Piperales as Peperomiaceae and Piperaceae, as done by certain taxonomists, with Peperomia repre-senting a primitive state in evolution.