Ruellia and Dianthera: An Anatomical Study

Abstract

With the exception of the polystelic axis in Dianthera, the structure of the two plants agrees well with that of Acanthaceae in general as recorded by SOLEREDER, namely, the type of stomata, the glandular and simple hairs, the cystoliths, the raphidines, the various crystals of calcium oxalate, etc. These characters are some of the most important for distinguishing the family. Although Ruellia and Dianthera possess the principal characteristics of the family, the very different environment in which they live has been the immediate cause of several modifications in structure. In Ruellia the structure is that of a land plant as follows: the hairy root with a solid cortex and with many sclerotic cells; the very hairy stem with a closed sheath of stereome inside the endodermis; the very hairy leaves held in a horizontal position and with a strictly bifacial structure in regard to stomata and palisade tissue. In the aquatic Dianthera, on the other hand, the roots are glabrous (at least in adult specimens) and the cortex is collapsed; the stem has only small, glandular hairs and the cortex shows intercellular spaces of sometimes enormous width; the narrow leaves are held in a vertical position and are approximately isolateral, so far as concerns the stomata and palisade cells; in addition to the glandular hairs only very short and mostly unicellular hairs cover the margins of the younger leaves.