PROBLEMS OF ANTIPODAL DISTRIBUTION IN LOWER LAND PLANTS

Abstract

Summary The geographical distribution of the more primitive Hepaticae (subclass Jungermanniae) exhibits the same patterns of endemism and disjunction, and highly specific and restricted ranges as found in many groups of vascular plants. The subantarctic region is shown to have an unduly high preponderance of primitive genera present (ca. 50% of all known unspecialized types), of which very many are strictly endemic there. Many of these groups are cold‐adapted types which seem to have exhibited only limited displacement northward as a result of late‐Tertiary and Pleistocene deterioration of the climate; others (Blepharostomataceae) have shown some striking dispersal to the cold regions at the opposite side of the globe, but the bulk of taxa remain Antipodal. Other families (Gymnomitriaceae, Scapaniaceae) that seem to lack tolerance for warm climates are today very preponderantly Arctic subarctic (and Alpinesubalpine), but the most primitive taxa are still strictly subantarctic, leading to the conclusion that these largely Holarctic families are originally Panantarctic. From the evidence given it is concluded that many but probably not all major groups of the Jungermanniae may have originated in this Panantarctica (Gondwanaland). The recent overwhelmingly “in phase” data corroborating the theory of continental drift, plus the relatively late times for separation of the Australian‐Tasmanian‐New Zealand area from Antarctica (ca. 40‐60 m.y. ago; perhaps somewhat earlier in the case of New Zealand) suggest much of the dispersal (of older, unisexual taxa) may have been overland during late Mesozoic and early Tertiary times. Ranges of some taxa on islands near or on the Mid‐Atlantic and Indian‐Ocean ridges, islands which vary from 1‐20 million years in age, clearly indicate some taxa (especially bisexual ones) may have wider powers of spore‐dispersal than sometimes assumed. Present evidence does not, often, allow us to distinguish between ancient “overland” dispersal, and more recent dispersal via spores.

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