The genus Gibsmithia (Dumontiaceae, Rhodophyta) in Australia

Abstract

Until now, the genus Gibsmithia has been monotypic, with the type species (G. hawaiiensis Doty) recorded only from Hawaii and French Polynesia. In this paper, the type species is reported from tropical eastern Australia, as are the two new species G. doyti and G. larkumii. A third new species, G. womersleyi, is described from the cool-temperate southwest of Australia. All are characterized by lengthy (6-16 celled) carpogonial filaments bearing sterile laterals on their lower cells; auxiliary-cell filaments terminated by sterile cells shaped like normal vegetative cortical cells; globular cystocarps subtended by a lax involucre of filaments produced prior to gonimoblast initiation by lower cells of the auxiliary-cell filament; and decussately cruciate tetrasporangia borne on isomorphic tetrasporophytes. Plants of all but G. larkumii consist of cartilaginous, presumably perennial stalks bearing gelatinous, annual blades. Gibsmithia larkumii is distinguished by its lack of stalks and the non-clustered arrangement of its tetrasporangia. Gibsmithia hawaiiensis is unique in producing callithamnioid cortical filaments that extend beyond the gelatinous matrix of the frond. Gibsmithia womersleyi is the most robust (up to 48 cm long) of the species and has angularly contoured generative auxiliary cells in contrast to the other species. Gibsmithia dotyi is the most variable of the species in habit and anatomy; it tends to produce initially flattened and rosulate blades, and its tetrasporangia are concentrated in the mid-cortex. Apart from their distinctive habits, members of the genus are unique among the Dumontiaceae in forming lateral cell protrusions that fuse with cells of adjacent medullary or inner cortical filaments, resulting in much cross-linking of the tissue.