Vers une Classification Phylogénétique des Espèces du Genre Riccia

Abstract

Presently only about half of the species of the genus Riccia are well known, but the available data can be used to propose a phylogenetic classification. The following are discussed: The origin of Riccias by the late Paleozoic Era or the Triassic Period of the Mesozoic Era, the possible life conditions from the arid Mesozoic to the present, the interpretation as primitive of those general characteristics common to all species, the interpretation of unique features as adaptive or evolu- tionarily advanced and the phylogenetic interpretation of spore morphology and micromorphology. Spores retained in tetrads are considered archaic to dissociated spores. Spore surface ornamentation is indicative of the degree of evolution. Chemical, cytological and ontogenetic peculiarities are insufficiently known to aid in phylogenetic determinations. Certain taxa are more significant than others as evolutionary indicators: R. caroliniana, an archaic species, a kind of living fossil; R. membranacea with small, verrucose, spherical spores; R. perssonii with echinulate, undivided spores and Riccia sect. Pilifer, a recent taxon as shown by geographic distribution. A scheme is provided in an attempt to indicate the hypothetical phylogenetic relationships among species groups.