MORPHOLOGICAL ADAPTATIONS OF THE JUNGERMANNIALES (HEPATICAE) TO THE TROPICAL RAINFOREST HABITAT

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  The Jungermanniales are most diverse and abundant in the tropical rainforest habitat. The most important parameters influencing their growth in this environment are relative humidity, rainfall, light, and temperature. Stems, leaves and reproductive organs have structural modifications with possible adaptive significance in this habitat. Adaptations involving the stem are growth habit (projecting, prostrate, and rheophytic) and stem anatomy (epidermal thickenings, stem reduction and stem flattening). Modifications to leaf structure include development of simple and complex saccate leaf lobules and differentiation of elongate, thin-walled cells within the leaf. Adaptive features relating to the dispersal and establishment of diaspores include the secretion of sticky mucilage in conjuction with gemma production, the development of discoid gemmae, precociously germinating spores, prolongation of the protonemal stage and development of a neotenic life cycle.