AN ACCOUNT OF AUSTROLITHON INTUMESCENS GEN ET SP-NOV AND BOREOLITHON VAN-HEURCKII (HEYDRICH) GEN ET COMB-NOV (AUSTROLITHOIDEAE SUBFAM NOV, CORALLINACEAE, RHODOPHYTA)

The Austrolithoideae (subfam. nov.), comprising Austrolithon (gen. nov.) and Boreolithon (gen. nov.), differs from other subfamilies in the Corallinaceae (Corallinales, Rhodophyta) in possessing multiporate tetrasporangial conceptacles and in lacking cell fusions, secondary pit connections and genicula. Austrolithon and Boreolithon both include single known species: A. intumescens (sp. nov.) from southern Australia and B. van-heurckii (comb. nov.) from the British Isles and France. Austrolithon and Boreolithon differ in growth form (unconsolidated vs. encrusting), habit (almost entirely endophytic vs. epigenous) and thallus construction (partly diffuse and partly pseudoparenchymatous and monomerous vs, largely pseudoparenchymatous and dimerous). Type material of both species was examined. A detailed morphological and anatomical account of Austrolithon intumescens is provided and new data are presented for Boreolithon van-heurckii. Information on etymology, collections examined, and distribution, seasonality and habitat is also included for both species, and Austrolithon intumescens is compared with other endophytic Corallinaceae. Eight subfamilies of Corallinaceae are now recognized, based on phenetic comparisons; similarities and differences are considered briefly.