The Cytogeography of Impatiens L. (Balsaminaceae)

Abstract

Many plant genera are known to include species with different basic chromosome numbers; such occurrences are generally of interest, but more particularly when cytological variation of this sort is correlated with changes in growth form, reproductive behaviour or distribution. Impatiens L. is a genus of this type-one in which both variation in basic number and the incidence of polyploidy show decided geographical patterns. Recent studies at the Jodrell Laboratory, Kew, make a significant contribution to this knowledge and form the basis for this first report. Impatiens is essentially a montane genus of the Old World containing over 500 species, half of which occur in the sub-continent of India. It is common in Burma and Africa but less so in SE. Asia and is relatively rare in northern Asia, Europe and North America. There is no taxonomic monograph of the genus and the only significant attempts at classification of the species are those of Hooker (1874-5) and again Hooker (1904-6). The classifications are markedly different in the two works due to the discovery of many more species in the intervening years. It had also become more apparent that endemism was prevalent and this resulted in a primarily phytogeographic treatment of the species in the later work. More recently it has been estimated that as many as 91 per cent. of the Indian species are endemics (Chatterjee, 1940: 44)Cytological studies have also been few in number and, prior to the present study, only twenty-three species had been chromosome counted. The latest and most substantial contributions have been made by Khoshoo (1955, 1956, 1957) who, in his I957 paper, lists and reviews all the previous works. At that time two main cytological characteristics of the genus emerged, namely that it was exclusively diploid and that the basic numbers of the species showed considerable variation (x = 6, 7, 8, Io). Although limited, the combined data also suggested that x = 8 might be typical for African species.