Sgouracanthus hannafordii gen. et comb. nov. and Sgouracantheae trib. nov. (Wrangeliaceae, Ceramiales, Rhodophyta) from southern Australia

The rare southern Australian rhodophyte, previously known as Ptilota (?) hannafordii Harvey 1862, is morpho-anatomically re-examined and the new genus Sgouracanthus and tribe Sgouracantheae are proposed to accommodate it. Thalli of Sgouracanthus hannafordii may reach 38 cm in length and grow individually in the sublittoral zone (to 33 m depth) attached to rock and macroalgae, although most records are from drift specimens bearing debris and grit among its curly and spiny branches. Sgouracanthus exhibits whorl-branches of determinate growth bearing procarps on their basal cells, which characterizes basal members of Ceramioideae, but the new genus is here classified in the Wrangeliaceae on account of oblique apical divisions, dense cortication, lack of gland cells, elongate spermatangial heads, polysporangia, a distinctive fusion cell, and multinucleate vegetative cells. In addition, Sgouracanthus develops a single auxiliary cell and tetrahedrally divided subspherical tetrasporangia, characters found in members of both groups. The taxonomic analysis supports a position near Spongoclonium and Dasythamniella , which is in agreement with a gene phylogeny based on the nuclear small subunit rDNA.