Spirophycus acicularis, a new red algal genus and species in the Lophothalieae (Rhodomelaceae, Ceramiales) from eastern Australia

Abstract

Spirophycus acicularis A. Millar gen. et sp. nov. (Lophothalieae, Rhodomelaceae, Ceramiales, Rhodophyta) is a monotypic genus described from sublittoral habitats in the Solitary Islands Marine Park (29°47′S, 153°18′E), on the northern New South Wales coast of eastern Australia, near Coffs Harbour. Plants grow on the stalks of polychaete tube worms and consist of erect, subdichotomous, polysiphonous axes bearing a variable number of five to ten periaxial cells. Numerous pigmented, determinate, unbranched, monosiphonous trichoblasts are produced exogenously in a spiral sequence and bear the reproductive structures. Indeterminate laterals also arise exogenously in a similar manner to the trichoblasts. Spermatangial branches form compact clusters or heads around the apices of indeterminate, dwarf laterals but themselves lack sterile laterals. Tetrasporangia are borne in stichidia, which are modifications of trichoblasts, are produced one per segment, and are spirally arranged within the stichidia. Supporting cells of the carpogonial branches cut off only one sterile cell group. Plants show a superficial resemblance to Spirocladia barodensis and Lophocladia kuetzingii, but differ from these mostly by the unbranched nature of their trichoblasts and by the variable number of their periaxial cells. Spirophycus is considered to belong to the tribe Lophothalieae (even though the variable number of periaxial cells is alien to that tribe) and a dichotomous key to the included genera is offered. The variable number of periaxial cells is a feature which is shared with at least one genus (Schizochlaenion) of the tribe Brongniartelleae, and critical comparisions between these two tribes are made.