The Hyparrhenia involucrata—H. subplumosa (Gramineae) complex in Nigeria: morphological and cytological characterization

Hyparrhenia involucrata Stapf is an annual with diploid, aneuploíd, tetraploid and hexaploid chromosome races on a base of x = 10, whilst M. subplumosa Stapf is known to be tetraploid and perennial. The two species overlap considerably in their vegetative and floral attributes. Whilst the floral characteristics (such as number of awns and sex of imperfect flowers) are fairly constant within H. involucrata , they are quite variable in H. subplumosa : the evolutionary significance of some of these variations is discussed. Some of the observations on size, variability and fertility of pollen grains are interpreted using data from chromosome numbers and meiotic behaviour. Preliminary observations on the hybrids between a diploid race of H. involucrata and H. subplumosa indicate that the genomes of the two species are highly homologous and that perennial habit is a dominant trait controlled by a single gene.     

The Hybrid Origin of Emilia praetermissa (Senecioneae: Compositae)

Interspecific hybrids were obtained between Emilia coccinea(n = 5) and E. sonchifolia (n = 5). Except for quantitativecharacters such as plant size, head size, and leaf size, thediploid hybrid was similar to E. praetermissa (n = 10). Artificial polyploidization of the diploid hybrid resulted inan allotetraploid which is morphologically indistinguishablefrom E. praetermissa. The artificial tetraploid hybrid and E.praetermissa are also similar with respect to their karyotypesand their meiotic behaviours. Morphological and cytogenetic evidence suggest that E. praetermissaoriginated from a plant which is of hybrid origin and whichis similar to the synthetic tetraploid.     

Cytogenetic studies in the Andropogon gayanus—A. tectorum complex (Graminae)

Cytogenetic studies in the Andropogon gayanus—A. tectorum complex (Granimae). Studies on the morphology, karyotype and meiotic behaviour of collections of Andropogon gayanus [2 n = 40), A. tectorum (2 n = 20,30) and their hybrids, obtained by both open pollination and controlled crosses, have been made. The chromosome number of 2 n = 30 for A. tectorum is new. Karyotypic analyses of the species and the preponderance of trivalents at diakinesis in the triploid and aneuploid hybrids show that considerable homology exists between the genomes of the two species. The evolutionary relationship between the two species and the probable origin of tetraploid A. gayanus are discussed.     

Chromosome numbers in Nigerian Compositae

Chromosome counts are presented for 54 collections of Nigerian Compositae. The collections comprise 37 taxa belonging to 21 genera and 34 specieS. Most of the taxa studied are colonisers of disturbed habitats.