Apocynaceae

VI. Evolutionary role of numerical alteration in chromosomes in varietal differentiation in Plumeria

Abstract

Cytology of Plumeria rubra acutifolia (2 vars.) and Plumeria alba (2 vars.) was studied. The two varieties of Plumeria alba, a small-flowered var. and a large-flowered var. are morphologically quite similar, the only difference being in the size of the different plant parts and flowers. The chromosome number of small-flowered var. was 2n=36 and that of large-flowered var. was 2n=54. This shows that the large-flowered variety is a triploid and has been derived from small-flowered variety by a change in ploidy level. Further investigations on the karyotypes of these varieties revealed marked similarities of chromosome structure. This further supports the view that large-flowered, Plumeria alba is a autotriploid.