Species Diversity at Wet Tropical Environments II. Speciation of Schismatoglottis okadae (Araceae), an Adaptation to the Rheophytic Habitat of Mountain Stream in Sumatra

Abstract

Schismatoglottis okadae, a rheophytic species, was investigated on its distribution pattern, habitat, morphology, karyotype and population structure. The species is restricted to a few locations in West Sumatra which are separated from each other. In these places (locations) the species occurs only in the area near the stream. The stem and leaf show mat-rooted characteristic which is typical to other rheophytes. The chromosome number is 2n = 26 + 0∼8B. But, one structural mutation of chromosome is present and it can be applied for the analysis of colony structure just as the presence or absence of B-chromosomes. As the results, two kinds of colony structure have been detected: one is composed of homogeneous individuals, which seems to have propagated vegetatively, and the other is heterogeneous which would have developed from seedlings. The speciation of the group in the Barisan range is presumed to occur through the following processes: the geographical upheaval of the Barisan range provided the new ecological niche, rapid streams, for the rheophytic forms. The ancestral form of this species might have existed near the mild stream of the mountain plateau as to be seen in Airsirah plot site today, from which true rheophytic forms adapted to the rapid stream sides have been produced.