Morphology and taxonomy of the Dasyaceae and the Lophothalieae (Rhodomelaceae) of the Rhodophyta

Abstract

To date the knowledge of the family Dasyaceae has been obtained from species known only in the northern hemisphere, yet southern Australia is an important centre of distribution for species of this family.

These morphological studies on the Dasyaceae concern four species of Dasya (Dasya clavigera (Womersley) comb. nov. has been transferred from Dasyopsis), five species of Heterosiphonia and two species of Thuretia. Additional comments are made on a further species of Dasya and one of Heterosiphonia. New descriptions of the genera are given. Several features reported in the literature as being characteristic of the Dasyaceae are found to be inconsistent and it is shown that the development of the fusion cell, and the sympodial growth of the thallus, are good family characters.

Three genera of the tribe Lophothalieae (Rhodomelaceae) are studied because of their superficial similarity with species in the Dasyaceae. The type species of Lophothalia, Doxodasya and Haplodasya, and one other species of Doxodasya and Haplodasya (H. tomentosa sp. nov.) are studied in detail to provide an understanding of the tribe Lophothalieae. Haplodasya, once placed in the Dasyaceae, is removed to the Lophothalieae. Comparisons of the Lophothalieae with Brongniartella (as described in the literature) are made and the differences require the formation of a new tribe, the Brongniartelleae, to take Brongniartella and similar genera once placed close to Lophothalia.

It would appear that the Lophothalieae and the Dasyaceae are examples of parallel evolution of thallus form and are not closely related.

Two species of Dasya and two of Heterosiphonia were used in an attempt to culture these plants completely through their life cycle in the laboratory. Dasya clavigera has been successfully taken through its life cycle for two generations of sexual plants and one of tetrasporangial plants. No other species grew to reproductive maturity.