The Evolution of a Weed

Abstract

Abstract Saccharum spontaneum L. is an innocuous grass species of the Old World, but one of its ecotypes behaves as a pernicious weed in Central India. The species is believed to have evolved in the ecological mosaic of the sub-Himalayan valleys into a wide range of polyploids (2n = 40 to 128), from where its higher polyploids may have migrated into South-east Asia and Africa while the lower ones spread over the Indian sub-continent. The species shows much morphological diversity, and a remarkable plasticity and adaptation to environment. Its ecotypes propagate themselves variously, and many clones possess rhizomes for tiding over long dry seasons. The weed ecotype is one of the latter. When a collection of S. spontaneum clones was grown in an experimental garden, most of the clones from the Himalayan river basins and the larger deltas showed no tendency to rhizome formation, while almost all occurring in the Central Indian plateau were highly rhizomic; the lower peninsular clones showed various degrees o...