Studies in the Gramineae: VI

Abstract

Sporobolus indicus, sensu latissimo, occurs throughout the tropics and subtropics. It is polymorphic and a number of separate species have been recognized within the complex, but the extent to which these species are linked by an almost continuous range of intermediates has led to considerable confusion. At first sight there appears to be no other course than to regard the complex as a single variable species. But on closer examination it becomes clear that the majority of the specimens are aggregated about a limited number of foci, each associated with a particular geographical distribution, and the intermediates, although most troublesome taxonomically, are numerically of lesser importance. It is thus possible to recognize a number of taxa, while admitting that in every attempt to formulate exact and mutually exclusive diagnoses one is bound to stumble over the question of intermediates. Their taxonomic status is far from clear, and much cytogenetic investigation will be required before we have a sound understanding of the complex. Some of them are undoubtedly good species (it is noteworthy that at least 5 different chromosome numbers have been recorded within the complex), while for others hybrid or sub-specific rank might be more appropriate. For the present purpose I have treated them as species, since this involves least change in nomenclature, and an elaborate hierarchy with many new combinations is inappropriate in the present uncertain state of our knowledge. This approach will at least serve to focus attention upon the main morphological groups whose status and interrelationships deserve further investigation by the cytogeneticist.