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Phylum Phaeophyta – Order Chordariales

Thallus (sporophyte) discoid, 0.5–5 mm across, consisting of a monostromatic (occasionally distromatic in some genera) layer of prostrate radiating filaments either closely associated into a radially symmetrical thallus or somewhat irregular with the radiating filaments partly separated from each other, with each cell producing a short, free, unbranched or occasionally branched filament 2–10 cells long and of uniform height, or a phaeophycean hair (with or. without a basal sheath), or a reproductive organ; epiphytic. Growth largely apical, from the marginal cells of the disc or the terminal cells of the erect filaments; germination stellate or unipolar, with heteroblasty common. Gametophyte usually of branched filaments.

Reproduction: Reproduction by meiospores from unilocular sporangia on the sporophyte and by isogametes from plurilocular gametangia on the gametophyte; the zooids from unilocular organs may also act as gametes, and zooids from plurilocular sporangia may reproduce the sporophyte directly in some species; plurilocular organs uniseriate or biseriate.

Life history heteromorphic but not markedly so.

Taxonomic notes: Loiseaux (1967a) recognised three tribes in the Myrionemataceae, and (1967b) investigated the life history of several species. The tribe Myrionemeae has a monostromatic disc, erect filaments from all disc cells and of equal height, and uni- or biseriate plurilocular organs; the Hecatonemeae have a partly distromatic disc, erect filaments not from all disc cells and of uneven height, and pluriseriate, lanceolate plurilocular organs; and the Ralfsieae have a pluristromatic thallus and erect filaments of equal height. The Ralfsieae are considered below as the family Ralfsiaceae. Pedersen (1984) regards the Hecatonemeae as including microthalli of members of the Punctariaceae and believes that Hecatonema is related to this family rather than the Myrionemataceae; Hecatonema is referred below to the Dictyosiphonales.

The Myrionemataceae include several genera (Parke et al. 1976, p. 559) as well as Myrionema. Compsonema is similar to Myrionema in having a monostromatic base, but differs in having multiseriate plurilocular sporangia (Setchell & Gardner 1922, p. 353) and also in having a single, sinuate or lobed, phaeoplast (Kuckuck 1953, p. 318). Chilionema is similar to Hecatonema in having the cells of the disc often divided horizontally, and differs in having the erect filaments unbranched and with terminal sporangia and hairs (Kuckuck 1953, p. 318).

Species of both Compsonema and Chilionema appear to be present on seagrasses and larger algae on southern Australian coasts, but these have not as yet been described. In view of the likelihood of their being stages in the life history of larger brown algae, and the need for culture studies to assess their position, they are not included in this account. Chilionema may well be better placed in the Punctariaceae, as with Hecatonema.

Pedersen (1984, p. 68) has shown that Myrionema-like microthalli occur in several genera of Chordariaceae, and he considers at least some species of Myrionema to be derived by regressive evolution from the Chordariaceae, as hypothesized by Loiseaux (1972).


KUCKUCK, P. (1953). Herausgegeben von P. Kornmann. Ectocarpaceen-Studien I. Hecatonema, Chilionema, Compsonema. Helgol. wiss. Meeresunters. 4, 316–352.

LOISEAUX, S. (1967a). Morphologie et cytologie des Myrionématacées. Rev. Gén. Bot. 74, 329–347, Plates 1–3.

LOISEAUX, S. (1972). Variations des cycles chez les Myrionématacées et leur signification phylogénétique. Mem. Soc. bot. Fr. 1972, 105–116.

PARKE, M., DIXON, P.S., RUSSELL, G. & FLETCHER, R.L. (1976). In Parke, M. & Dixon, P.S. Check-list of British marine algae-third revision. J. mar. biol. Ass. U.K. 56, 527–594.

PEDERSEN, P.M. (1984). Studies on primitive brown algae (Fucophyceae). Opera Bot. 74, 1–76.

SETCHELL, W.A. & GARDNER, N.L. (1922). Phycological Contributions II to VI. Univ. Calif Publ. Bot. 7, 333–426.

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
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