Meiotic Studies and Taxonomic Considerations in Some Taxa of Verbenaceae

抄録

Phenotypic plasticity and variations in chromosome numbers within the genera of the family Verbenaceae are known (Sharma and Mukhepadhyay 1963, Fedorov 1974). Fruits and seeds are formed sparsely off and on in most of the species of the genus Clerodendrum L. C. speciosum D' Ombrain has been considered to be a hybrid (Bailey 1949), but no cytological data have been adduced to support this contention. Whether a taxon is fully cytologically stable species or variety, heterozygous/homozygous, natural hybrid or comprised of translocated or inverted segments etc. can be clearly brought out by meiotic analysis (Stebbins 1971). Therefore, meiotic studies in commonly distributed nine species covering four genera viz. Clerodendrum L; Holmskioldia Retz; Petrea Houst, ex. Linn. and Lantana L. of the family Verbenaceae were carried out to determine their pure/hybrid nature, chromosomal behaviour during microsporogenesis and phylogenetic relationship.
Meiotic pairing in six species of the genus Clerodendrum L. revealed lower frequencies of rod bivalents than ring bivalents. All most equal frequencies of rod and ring bivalents per nucleus in H. sanguinea Retz. and L. camara Linn. have been observed. In P. volubilis Jacq. Queens Wreath; rod and ring bivalents frequencies are 6.4 and 10.8 respectively. Not more than two chiasmata per bivalent have been recorded in any of the taxa investigated. Higher chiasma frequencies were seen in all the six species of Clerodendrum investigated than that of H. sanguinea, L. camara and P. volubilis. The meiotic behaviour of chromosomes stressed that each species has come to possess its own genotypic behaviour and cytological performance. No cytological configurations to indicate the hybrid nature of C. speciosum were detected. However, cryptic structural hybridity might have led to the formation of abortive pollen grains and seeds in C. speciosum.