Rheophytes are plants confined to the beds of swift-running streams and rivers, growing above flood level but not beyond the normal reach of flash floods. Leaf morphoanatomy of the rheophyte Raulinoa echinata R.S.Cowan (Rutaceae) was investigated with a focus on understanding adaptation to the peculiarities of the rheophytic habitat. R. echinata leaves are dorsiventral and hypostomatic. The epidermis has a single layer of cells and the stomata are anomocytic. The guard cells rise above the level of the other epidermal cells (a hydromorphic characteristic), but with a conspicuous outer cavity (a xeromorphic characteristic). Prominent traits related to the rheophytic habitat are stenophylls and the presence of suberin on the inner periclinal walls of the epidermal cells. Leaf area varies with sun exposure while stomatal density varies with river flow. In R. echinata, mesophyll tissue thickness varies with light intensity and river flow. Secretory cavities and idioblasts with calcium phosphate crystals occur in the mesophyll. The data revealed leaf-structure plasticity in relation to the singular conditions of the rheophytic environment as well as to shade or sunlight.
rheophytes; Raulinoa echinata; adaptative characteristics; anatomy; leaf
