DEVELOPMENTAL PROBLEMS IN SELAGINELLA (SELAGINELLACEAE) IN AN EVOLUTIONARY CONTEXT

The antiquity and diversity of Selaginella species attest to the evolutionary success of the genus. This success may be attributed, in part, to certain morphological and anatomical features that characterize Selaginella. Recent developmental studies of anisophylly, monoplastidy, the ligule, the rhizophore, marginal warty cells, and marginal teeth of the leaves, as well as aspects of the heterosporous life cycle are discussed. Unresolved questions concerning vegetative features include the function of the ligule, morphological interpretation of the so-called rhizophore, and a possible role of distinctive leaf ornamentations in water economy. Among unresolved questions concerning reproductive morphology are the basis of heterospory, control of sporangial development, spore dispersal mechanisms as they affect inbreeding and outcrossing, and other details of the reproductive process. It is concluded that the genus Selaginella offers numerous opportunities for future research.