Electronic Flora of South Australia Family Fact Sheet

FAMILY SCYTOTHAMNACEAE Womersley fam. nov.

Phylum Phaeophyta – Order Chordariales

Thallus (sporophyte) usually 2–20 cm long, erect, with a small holdfast bearing much branched, cylindrical fronds or simple and clavate vesicles, epilithic. Structure multiaxial, with a filamentous medulla (which may largely disintegrate and become mucilage filled) and compact, pseudoparenchymatous, assimilatory cortex of anticlinal filaments, with cells smaller outwardly; phaeoplasts stellate or discoid; phaeophycean hairs clustered and confined to depressions or cryptostomata in the cortex. Growth apical and subapical, with periclinal divisions and anticlinal or oblique divisions in epidermal cells producing branched filaments.

Microthalli filamentous or discoid, gametophytic.

Reproduction: Reproduction by unilocular meiosporangia borne within the cortex, by transformation of cortical cells or cut off laterally from subapical cells of cortical filaments, scattered or forming vague sori. Gametophytes by plurilocular dioecious gametangia producing isogametes.

Life history diplohaplontic and heteromorphic, or direct (Clayton 1986).

Taxonomic notes: This family is based on Scytothamnus (and Adenocystis is also included) and was first suggested but not described by Setchell & Gardner (1925, p.570). Recently it has also been supported by Clayton (1985, p.295), who, along with Price (1969) and Asensi (1975) shows that both Scytothamnus and Adenocystis are haplostichous and hence should be placed in the Chordariales. The life history has been elucidated by Clayton (1986). The family is characterised by the multiaxial, haplostichous thallus with apical and subapical cell divisions, a pseudoparenchymatous cortex, hairs in clusters in depressions or cryptostomata and sporangia scattered in the cortex. It differs from the related Splachnidiaceae in the sporangial situation (not in conceptacles) and in the absence of the pyriform "apical cells".

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. (1985). A critical investigation of the vegetative anatomy, growth and taxonomic affinities of Adenocystis, Scytothamnus and Splachnidium (Phaeophyta). Br. phycol. 1 20, 285–296.

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.

PRICE, I.R. (1969). The structure and classification of Scytothamnus australis (J. Agardh) J.D. Hooker et Harvey (Phaeophyta). Phycologia 8, 37–41.

SETCHELL, W.A. & GARDNER, N.L. (1925). The marine algae of the Pacific coast of North America. Part III. Melanophyceae. Univ. Calif Publ. Bot. 8, 383–898, Plates 34–107.

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 GENERA OF SCYTOTHAMNACEAE

1. Thallus much branched, branches 0.5–2 (–4) mm in diameter; phaeoplasts stellate or discoid; sporangia scattered, subspherical to ovoid, transformed from cortical cells

SCYTOTHAMNUS

1. Thallus with few to several simple, clavate, saccate, vesicles from a small holdfast, (2–) 4–6 (–10) cm long and 0.5–2 (–3) cm in diameter; phaeoplasts discoid; sporangia clavate, borne laterally from subapical cells of cortical filaments in vague sori

ADENOCYSTIS


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