A biological study of Desmarestia firma (C.Ag.) Skottsb. (Phaeophyceae, Desmarestiales)

Doctoral Thesis


Permanent link to this Item
Journal Title
Link to Journal
Journal ISSN
Volume Title

University of Cape Town

Several aspects of the biology of Desmarestia firma (C.Ag.) Skottsb., a common understorey alga in western Cape (Southern Africa) kelp beds, are investigated. The life-history of this species is described from culture. Zoospores from unilocular sporangia give rise to separate filamentous male and female gametophytes. Male gametophytes bear flask-shaped antheridia, each containing a single antherozooid. Female gametophytes bear club-shaped oogonia, each producing one or perhaps more eggs. Trichothallic sporophytes are fused to the female gametophytes. Specimens were cultured to a stage where they produced rhizoids and cortication became apparent. This is the first description of the life-history of a branched, ligulate Desmarestia species, and refutes the suggestion that in oppositely branched species, gametophytes are monoecious. Nomenclatural problems associated with D. firma are discussed, and the taxonomic relationships of D. firma and closely related species are investigated. Results show varying degrees of morphological overlap between this entity and certain others from North West America, South America and Morocco. Microscopic examinations show that sporophytes from New Zealand, Gough Island, South America and N.W. America have the same reproductive anatomy as D. firma, i.e. with sporangia scattered among, and similar in size and shape to the cells of the outer cortical layer. Material from the South Orkney Islands shows sporangia interspersed with sterile paraphyses and arranged in an elevated sorus. The taxonomic implications of these results are discussed, and the name D. firma is provisionally retained for the Southern African entity.

Bibliography: leaves 212-232.