ASPECTS OF PERMIAN PALEOBOTANY AND PALYNOLOGY .17. CONIFER EXTINCTIONIN EUROPE AT THE PERMIAN-TRIASSIC JUNCTION - MORPHOLOGY, ULTRASTRUCTURE AND GEOGRAPHIC STRATIGRAPHIC DISTRIBUTION OF NUSKOISPORITES DULHUNTYI (PREPOLLEN OF ORTISEIA, WALCHIACEAE)/

The genus Ortiseia is the youngest representative of the Walchiaceae, a presently well-defined family of Late Carboniferous/Permian conifers , characterized by zoidogamy. Species of Ortiseia are a prominent comp onent in the xerophilous Late Permian flora of the Southern Alps. Thes e species produced pollen grains corresponding to the palynological sp ecies Nuskoisporites dulhuntyi. In order to minimize the risk of corre lating similar but not identical dispersed pollen with Ortiseia, contr oversies and uncertainties as to the morphological organization of N. dulhuntyi are resolved by applying both light-and electron-microscopy (SEM, TEM). An emended diagnosis is presented. Ultrastructural analysi s verifies the absence of a distal aperture; a prepollen condition is therefore emphasized. Confirmed occurrences of N. dulhuntyi remain res tricted to the Upper Permian of western, central and southern Europe. First-occurrences are not earlier than Wordian times. Last-occurrences approximate the Permian-Triassic boundary and match worldwide evidenc e of dieback of arboreous vegetation in the terrestrial biosphere. The deduced extinction of Ortiseia exemplifies the effects of the Permian -Triassic biotic crisis on gymnosperm diversity in the European part o f the late Palaeozoic Euramerican floral realm.