Evolutionary Morphological and Molecular Systematical Study of Rheophytes

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1.A Comparative leaf anatomical study of tropical rheophytes and closely related dryland species demonstrated that the rheophytes have smaller mesophyll cells, epidermal cells, and intercellular space as well as the thicker cuticular layr and epicuticular waxs, than the dryland species. These anatomical features are strongly correlated to the narrow leaves of rheophytes.2.During the leaf development of the rheophytic Osmunda lancea and the dryland O.japonica, whereas they are similar at the cell increment stage, there is a distinct difference in the cell enlargement stage. The cell increment stage in O.lancea is shorter than in O.japonica, suggesting heterochrony(progenensis).3.In order to examine the adaptive strategy of rheophytic gametophytes, a comparative developmental study of gametophytes of O.lancea and O.japonica was made. The gametophytes of O.lancea grow faster to reach reproductive maturity and produce sporophytes at higher frequency than those of O.japonica. The rheophytic gametophyte takes a strategy different from that of the dryland gametophyte.4.In the field the dryland O.japonica is removed from a rheophytic zone during a young (1-year old) developmental stage of sporophyte. Morphological and anatomical differences of leaves between O.lancea and O.japonica appear at the 5th or 6th youngest leaf stage, corresponding with the populational change in the field.5.A broad-leaved variant of the rheophytic Tectaria lobbii shows quite a small genetic divergence from the rheophyte and a remarkable anatomical similarity to dryland species.