Electronic Flora of South Australia Family Fact Sheet
Thallus (sporophyte) erect, usually 10 cm-10 m long, much branched oppositely or alternately, terete to slightly or strongly compressed or foliose, complanate, with or without a midrib and lateral veins, with feathery end filaments to actively growing branches, attached by a discoid or hapteroid holdfast. Growth trichothallic with a meristem near the base of the apical filament to each branch, branching oppositely to give lateral filaments which become separated on the axial filament by intercalary divisions, and below the meristem developing a pseudoparenchymatous (haplostichous) cortex by corticating rhizoidal cells which later divide periclinally to form a large-celled medulla around the axial filament and a small-celled cortex. Structure with the axial filament remaining more or less conspicuous, surrounded by the large-celled cortex with small-celled hyphae around the axis and between the cells; cortical cells with numerous, discoid, phaeoplasts, without pyrenoids. Phaeophycean hairs absent.
Reproduction: The sporophyte by unilocular meiosporangia developed singly from only slightly modified cortical cells, or in sori with or without paraphyses, or in a moniliform series on free, branched, uniseriate filaments on the thallus surface, producing zoospores. Gametophytes monoecious or dioecious, oogamous.
Life history diplohaplontic and heteromorphic, with a conspicuous sporophyte and a filamentous, microscopic gametophyte.
Taxonomic notes: The Desmarestiales is a small order of two families and 4 or 5 genera. They are essentially cold water taxa, and the cold temperate Desmarestia ligulata is known from odd specimens on south-east Australian coasts. The other taxon, Arthrocladia villosa, is probably an introduction from Europe and may not have become established on our coasts.
References: The Marine Benthic Flora of Southern Australia Part II
Womersley, H.B.S. (14 December, 1987)
The Marine Benthic Flora of Southern Australia
©Board of the Botanic Gardens and State Herbarium, Government of South Australia
KEY TO FAMILIES OF DESMARESTIALES
1. Thallus filiform to flattened, with laterals opposite; sporangia in or on the surface cortical layer, scattered or grouped into sori
1. Thallus filiform, with laterals in whorls of four; sporangia in moniliform chains on branched, uniseriate filaments external to the vegetative branches
State Herbarium of South Australia