H. Liebenberg et al., CYTOTAXONOMIC STUDIES IN THEMEDA-TRIANDRA FORSSK .4. A POPULATION CYTOGENETIC STUDY OF A CONTACT ZONE BETWEEN TETRAPLOID AND HEXAPLOID POPULATIONS, South African journal of botany, 59(3), 1993, pp. 305-310
A population cytogenetic study was undertaken across a contact zone be
tween Themeda triandra populations in the Transvaal Bushveld to the no
rth of the Magaliesberg, and Highveld populations to the south. Fiftee
n collection points were chosen and three plants collected at each poi
nt. The northern-most collection point contained only tetraploids and
those on the Highveld only hexaploids. In the vicinity of the Magalies
berg Mountain range, contact between the tetraploids and hexaploids pr
oduced pentaploid and decaploid hybrids. Meiotic pairing association a
nalyses showed that both the tetraploids and hexaploids formed apomict
ic clones, of which some were widely distributed and others were more
limited. This indicates that facultative apomixis occurs among both th
e tetra- and hexaploids and gives rise to genotypic and genomic segreg
ants thus producing variation and forming new apomictic clones. The po
ssible evolution of Themeda triandra in southern Africa is discussed.