Cytogenetics of Cultivated Bougainvilleas Vii: Origin and Evolution of Ornamental Taxa

Bougainvilleas have a short history of domestication. In about 150 years, when they were first brought into cultivation outside their native home (South America), a large number of forms have arisen from a meagre basal stock of three species. Much of the evolution took place outside their native home and the primary factor has been natural hybridization which was enhanced by nectariferous flowers and showy bracts, accompanied by self-incompatibility. However, no planned hybridization work has been carried out and all seedlings were raised from spontaneous seed formation. Two types of spontaneous bud sports have occurred from time to time, one resulting into variegated leaf pattern and other affecting the colour of bracts. The bud variations have been maintained and fixed by vegetative propagation.

With the introduction of bougainvilleas from their native tropical-sub-tropical climatic conditions to temperate conditions of european countries, the principles of selection of varieties for a particular climate varied. While floriferous character, extended blooming period and colour diversity were common under both climates, factors like growth habit and cold hardiness were taken care of, where it was grown under cover.

Various factors that have been responsible for evolution of new variants include. Outbreeding system (self-incompatibility), which enhanced spontaneous hybridization, and the changed gene-cytoplasm interaction of hybrids caused an increse in frequency of somatic mutations. Polyploidy and chromosomal repatterning have also contributed towards the origin of a few variants.