Electronic Flora of South Australia Genus Fact Sheet

Genus SCYTOTHAMNUS Hooker & Harvey 1845: 531

Phylum Phaeophyta – Order Chordariales – Family Scytothamnaceae

Thallus much branched with one to numerous main axes giving rise to several orders of branches, irregularly radially arranged, terete to slightly compressed, solid or becoming hollow, not or only slightly mucoid, usually 5–20 cm long with branches 0.5–2 (–4) mm in diameter, attached by a small discoid holdfast. Medulla multiaxial and haplostichous, with a group of apical cells dividing subapically producing filaments of elongate cells which form an outer medulla of closely appressed filaments and an inner medulla of looser filaments and interwoven hyphae, largely longitudinally orientated. Cortex dense, produced from outer medullary cells, consisting of radial rows of 2–5 cells, fairly closely associated laterally and in some cases pseudoparenchymatous, consisting of more or less isodiametric cells. Phaeoplasts stellate or lobed, with a central pyrenoid, or more or less discoid with a lateral pyrenoid in some cells. Phaeophycean hairs grouped, developing in shallow to deep cryptostomata in the cortex.

Reproduction: Reproduction by relatively large, ovoid to globose, unilocular meiosporangia formed from inner cortical cells and immersed in the cortex but reaching to the surface. Microthalli gametophytic, dioecious, with plurilocular gametangia producing isogametes (Clayton 1986).

Life history diplohaplontic and heteromorphic, with a filamentous gametophytic microthallus (Naylor 1956; Asensi 1975) producing isogametes (Clayton 1986), or sporophytes directly.

Type species: S. australis (J. Agardh) Hooker & Harvey.

Taxonomic notes: A genus of two species, confined to southern hemisphere cool temperate to subantarctic waters, distinguished by the multiaxial, haplostichous thallus with a well-defined cortex of short filaments of isodiametric cells, together with the large, ovoid sporangia within the cortex and hairs grouped within cortical cryptostomata.

References:

ASENSI, A.O. (1975). La estructura, la distribucion y el cultivo de Scytothamnus fasciculatus (Hook. et Harv.) Cotton (Phaeophyta). Physis (B. Aires) A, 34, 269–282.

CLAYTON, M.N. (1986). Culture studies on the life history of Scytothamnus australis and Scytothamnus fasciculatus (Phaeophyta) with electron microscope observations on sporogenesis and gametogenesis. Br. phycol. J. 21, 371–386.

HOOKER, J.D. & HARVEY, W.H. (1845). Algae Novae Zelandiae. Lond. J. Bot. 4, 521–551.

NAYLOR, M. (1956). A note on the life history of Scytothamnus australis H. & H. New Phytol. 55, 386–388.

The Marine Benthic Flora of Southern Australia Part II complete list of references.

Author: H.B.S. Womersley

Publication: Womersley, H.B.S. (14 December, 1987)
The Marine Benthic Flora of Southern Australia
Part II
©Board of the Botanic Gardens and State Herbarium, Government of South Australia

KEY TO SPECIES OF SCYTOTHAMNUS

1. Thallus robust, 1–2 (–4) mm in diameter, lesser branches 0.5–1 mm in diameter

S. australis

1. Thallus slender, axes usually 0.5–2 mm in diameter, lesser branches usually 200–500 µm in diameter

S. fasciculatus


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