Psilophycus alveatus gen. et comb. nov., a basal taxon in the Gigartinaceae (Rhodophyta) from New Zealand

The red alga Gigartina alveata (Turner) J. Agardh was collected by Joseph Banks in New Zealand in 1769 during Captain Cook's voyage on the Endeavour (1768-1771) and was originally described as Focus alveolus. This species forms a conspicuous band on rocky outcrops on open sandy beaches of the northern North Island in the mid-intertidal zone. The thallus is narrow, linear, channeled and repeatedly dichotomously branched, with the apices often curled and crowded, giving the plant a bushy appearance. Growth is multiaxial with the formation of parallel files of medullary filaments cross-linked by secondary pit connections in a reticulate manner. Cystocarpic plants greatly outnumber male or tetrasporangial individuals. Tetrasporangia are transformed from inner cortical cells, as in some basal lineages of Gigartinaceae, and secondary tetrasporangial filaments are absent. Spermatangial parent cells form spermatangia in clusters of four to live in pits surrounded by exerted cortical filaments. Procarps are typical for Gigartinaceae and consist of a supporting cell that bears a sterile cortical filament and a recurved three-celled carpogonial branch with the supporting cell functioning as the auxiliary cell. After presumed fertilization, cortical cells above the auxiliary cell form rosettes of small-celled filaments, and medullary cells undergo intercalary transverse divisions to produce modified cells that also bear rosettes of small-celled filaments. Gonimoblast filaments ramify through the medulla and may fuse with modified medullary cells, and carposporangial chains arise from these cells or directly from gonimoblasts. Surface cortical cells form a multiaxial meristem that surrounds the developing gonimoblasts to produce an envelope with an ostiole. A typical pericarp formed from secondary vegetative filaments is absent. In virtually every respect, the postfertilization development of the cystocarp is unique among members of the family Gigartinaceae and justifies the recognition of the new genus, Psilophycus, to contain the plant presently known as G. alveata.