Disjunct Hepaticae in tropical America and Africa

An increasingly large number of macrodisjunct species is emerging from recent literature dealing with taxonomy and floristics of tropical bryophytes. This paper reviews present knowledge concerning Afro-American disjunctions in Hepaticae and seeks to interprete the data in the light of current phytogeographical theory. Numerous new floristic records and range extensions are given and some taxonomic novelties are proposed. For 35 Afro-American species known three main distribution types are recognized, each further subdivided: Tropical Afro-American (lowland, montane and the alpine element), Subtropical-Mediterranean (southern, wide element) and Temperate-Subantarctic (southern, wide element). Most species belong to Jungermanniales except for the subtropical ones which are thallose. A few Afro-American genera, including the “peri-Afroamerican” Symbiezidium and Bryopteris, and vicariant species-pairs are also discussed. Among tropical taxa, lowland patterns are normally continuous, while montane and alpine patterns are typically “quadricentric” resp. “bicentric”. Deviating patterns may due to insufficient exploring or taxonomic knowledge, or relict nature. Several species are “weedy” and in the possession of excellent dispersal capacities; their occurrence in other palaeotropic regions is to be expected as well. Interpretation of dispersability is hampered, however, by the lack of experimental data on spore viability in liverworts (as contrary to mosses). It is postulated that macrodisjunct Afro-American species ranges in most cases should have arisen from successful transoceanic long-range dispersal whereas generic disjunction and species vicariance might be the result of ancient land connections, viz. evolution following the dissection of western Gondwanaland.