Chapter 5.pdf - DSpace@UM

Malesian species in general (especially those occurring within the wetter core areas)have more elliptic to broadly elliptic, sometimes to oblong (generally moreelongated) stomatal outlines, and outer stomatal ledges that are not very conspicuous(most of the species have intermediate coverage).It is noteworthy that a very limited number of specimens was used forstudying these characters in most of the species. Hence, the results obtained may nothave captured the whole variation that exists within the species. Only in the case ofR. pseudoternifolia (in var. pseudoternifolia), a sufficiently high number of sampleswere used. Hence, the large variation seen within this variety for most of theparameters (e.g., guard cell length and width; stomatal density; outer stomatal ledgelength and width; stomatal outline; and cuticular ornamentation of trichome) is notsurprising. According to Baas (1975), the variation below the species level(infraspecific variability) may be due to genetic variability or ecological factors. Forthis variety, it is likely that ecological factors could be significant because it is foundwithin a whole range of habitats (lowland to hill forests to c. 1640 m, includingkerangas forests, limestone and seasonal flood-plain areas).In some Malesian species, sections from the basal e.g., R. anisophylloides, R.kassamensis, R. macromera and R. uvarioides (New Guinea species) and the apicalportions, e.g., R. negrosensis (Philippines species) were used because ofunavailability of the mid-section portion. The apex section is considered the mostmature part of the leaf, while the basal portion the least mature (refer Stace, 1965).This may also contribute to the variation in character-states that were examined.According to Stace (1965), variation in cuticular characters may be due to threemajor causes, viz., age of the leaf or maturity; the environment in which the plant isfound and leaf position on the plant. Hence, it may not be surprising that characterssuch as stomatal density and size, and outer stomatal ledge aperture size, are to some176