An overview of chromosome and basic numbers diversity in cytologically investigated polypetalous genera from the Western Himalayas (India)

Abstract

Intensive exploration and evaluation of cytomorphological diversity has been carried out on 380 species of 127 genera belonging to 28 families of sub-class Polypetalae of flowering plants from Kashmir (Jammu and Kashmir) and Kangra and Sirmaur districts (Himachal Pradesh) of the Western Himalayas. The cytological investigations of these species over a period of three years revealed new and varied chromosome numbers for 100 species globally and 50 species in India, making a substantial addition to the knowledge of the genera to which these species belong. To obtain a comprehensive cytological picture of each of these genera, chromosomal data have been updated by compiling the literature on previous chromosomal numbers and supplementing it from the present studies. The final form is now ready to show the status both at global and Indian levels for various parameters like total number of taxonomically known species, number of cytologically determined species along with intraspecifically added number of cytological taxa, presently inferred basic numbers, level and frequency of polyploids, and information on number of species per genus carrying inter- and intraspecific euploid and aneuploid variability at the genus level. Of the total 127 genera, 39 genera have 75% or more cytologically worked out species. Addition of cytotypes in many cytologically known species has resulted in an enhanced number of chromosomal races/cytological taxa over such species, in the majority of genera, justifying the ever growing need to make population based intensive studies of any plant species. The data show that monobasic and dibasic genera are less common than tribasic and polybasic ones. Genera with x = 8 are most common, followed by x = 7 and x = 6. Of 127 genera, 47 genera exhibit polyploidy of up to 25%; 22 genera have 26–50%; 15 genera have 51–70%; and 26 genera have 76–100% polyploidy, while 17 genera lack polyploidy altogether. Interspecific and/or intraspecific euploid cytotypes such as diploids plus polyploids or with “polyploid series” are present in most of the 107 genera. Intraspecific aneuploid chromosome numbers are also shown by 100 genera. Since these genera belong to different families, so no generalization can be made at family level. However, at genus level chromosomal observations show the active role of various evolutionary processes responsible for chromosomal diversity in the majority of these genera distributed in the Western Himalayas of India.