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Karyotypes of six species of Barleria L. occurring in South India viz., B. acuminata, B. buxifolia, B. gibsoni, B. involucrata var. elata, B. noctiflora and B. strigosa are studied. All the six species have the same chromosome number of 2n=40. However, each species is distinct in respect of relative positions of centromere, presence/absence and position of satellites and total haploid chromatin length. The diagnostic value of the karyomorphological details in these taxa is discussed.

Three diploid interspecific hybrids and two reciprocal hybrids were produced between the species of section Erectoides. The cytological analysis in two hybrids and their reciprocal crosses shows 10 bivalents at diakinesis and metaphase-I in most of the PMCs and 2-4 univalents are seen in about 10 to 15 percent of cells. Further the hybrid between A. sp. 9990×A. sp. 10002 reveals a ring of four chromosomes in approximately 18 percent of the PMCs. In the hybrid A. regonii×A. sp 9990 and its reciprocal, chromatin bridge is seen in 8.4 percent of the cells at anaphase-II, thus providing cytological evidences for the possible role of structural changes in speciation of the section Erectoides.

BetweenThespesia populnea andT. lampas, more attention has been given to review the taxonomic status of the latter. The stigma ofT. lampas resembles with that ofT. populnea, whereas many other characters such as habit, gland on the midrib, non-caducous involucre, calyx teeth and capsule shape differ fromT. populnea. They also differ in their ecological adaptations. The chromosome number is found to be 2n=26 in both of them indicating their relationship. They also possess different chromosome numbers having 2n=28 inT. lampas and 2n=24 inT. populnea. Further, they fall apart from each other in size of the chromosomes. The cytological results and morphological characters, therefore, suggest the removal ofT. lampas fromThespesia.

The cause of sterility in Solanum wendlandii Hook. (2n=24) which is reproductively known to be a fertile plant in U.S.A. is revealed here by the desynaptic behaviour of chromosomes. The cytological observations reveal that only a few PMC's show normal behaviour of chromosomes. In most of the other cells, only a few bivalents are formed associated with varying number of univalents which range from 4 to 20 in a cell. Occasionally complete desynapsis has also been observed with 24 univalents. In addition, their behaviour at anaphase I and II is highly irregular. The unequal disjunction is a frequent phenomenon with a distribution of 2+22, 4+20, 6+18, 9+15, 10+14 etc., at the poles. The tetrad formation is also irregular. More than 60% of the pollen grains look empty. Thus there is a high degree of pollen sterility due to desynaptic behaviour of chromosomes, which may be due to partly genetical and partly environmental conditions.