Electronic Flora of South Australia Family Fact Sheet

ORDER CHORDARIALES Setchell & Gardner

Phylum Phaeophyta

Thallus (sporophyte) discoid or crustose and a few cells thick, or tufted, pulvinate or irregularly lobed and 2–20 mm thick, or terete, simple to much branched and 3–50 cm high; larger taxa usually mucoid; epilithic or epiphytic. Structure heterotrichous, of loosely to closely aggregated filaments, always haplostichous, usually differentiated into a medulla of relatively clear cells and a cortex of assimilatory, darkly pigmented filaments, with or without phaeophycean hairs, and bearing the reproductive organs. Growth by apical or subapical cells in discoid taxa, and apical, or diffuse, or trichothallic in cortical filaments of pulvinate or erect taxa. Phaeoplasts single to (usually) several per cell, discoid and each usually with a pyrenoid, or stellate and single (in Scytothamnus and Splachnidium).

Reproduction: The sporophyte by unilocular (usually meio-) sporangia or neutral plurilocular sporangia. Gametophytes isogamous, rarely anisogamous. Gametes in some taxa capable of parthenogenetic development.

Life history usually diplohaplontic and heteromorphic, the sporophyte macroscopic and gametophyte microscopic; or direct from zooids of either phase. Plethysmothalli present in some taxa (Wynne & Loiseaux 1976, p. 440).

Taxonomic notes: An order of some 11 families and over 60 genera (Wynne & Kraft 1981, p. 746; Wynne 1982, p. 116), of which 8 families occur on southern Australian coasts. The Chordariales include a rather heterogeneous group of families associated together in the one order by their heteromorphic life history and haplostichous construction, with intercalary parenchymatous divisions being absent, or, at least, rare. Growth varies from apical or subapical (e.g. Myrionemataceae, Ralfsiaceae, Spermatochnaceae) to trichothallic and multiaxial in many Chordariaceae.

While the Myrionemataceae are usually placed in the Chordariales, the Ralfsiaceae are more commonly placed in the Ectocarpales (e.g. Bold & Wynne 1985, p. 314) or as a separate order. However, they are related in habit and thallus construction to the Myrionemataceae and at least most of the Ralfsiaceae have, as far as is known, direct life histories (as do some Myrionemataceae). Both these families are therefore included in the Chordariales, as done by Kylin (1947), Taylor (1960) and Abbott & Hollenberg (1976).

Life history studies are needed on nearly all southern Australian Chordariales. In many species from elsewhere in the world it has been shown that the phase present is often dependent on the season, and in some cases the zygote develops into a microthallus which recycles via plurilocular sporangia until conditions are suitable for the adult sporophyte. The complexity and temperature dependence of the life histories has been shown by Milner (1981) for Spermatochnus, and many southern Australia taxa of Chordariales are only evident (as the macrothallus) during summer months.

The following keys apply to the sporophytic macrothalli and not, in general, to the microscopic gametophytic thalli or plethysmothalli.

References:

ABBOTT, I.A. & HOLLENBERG, G.J. (1976). Marine Algae of California. (Stanford Univ. Press: Stanford.)

BOLD, H.C. & WYNNE, M.J. (1985). Introduction to the Algae: Structure and reproduction. 2nd Edn. (Prentice-Hall: New Jersey.)

KYLIN, H. (1947). Die Phaeophyceen der Schwedischen Westkiiste. Acta Univ. lund. N.F. Avd. 2, 43(4), 1–99, Plates 1–18.

TAYLOR, W.R. (1960). Marine algae of the eastern tropical and subtropical coasts of the Americas. (Univ. Mich. Press: Ann Arbor.)

WYNNE, M.J. & KRAFT, G.T. (1981). Appendix. Classification Summary. In Lobban, C.S. & Wynne, M.J. (Eds), The Biology of Seaweeds, pp. 743–750. Bot. Monogr. Vol. 17. (Blackwell: Oxford.)

WYNNE, M.J. & LOISEAUX, S. (1976). Recent advances in life history studies of the Phaeophyta. Phycologia 15, 435–452.

WYNNE, M.J. (1982). Phaeophyceae. In Parker, S.P. (Ed.), Synopsis and classification of living organisms, Vol. I, pp. 115–125. (McGraw-Hill: New York.)

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 FAMILIES OF CHORDARIALES

1. Thallus crustose, discoid to spreading and 1 mm to several cm across, epiphytic or epilithic (or on wood), formed of radiating, prostrate filaments with all or most cells producing an erect or assurgent filament, a hair or a reproductive organ; growth of the filaments largely apical

2

1. Thallus tufted, globular or pulvinate, or erect and simple or branched, differentiated into a colourless medulla and outer assimilatory cortex of erect filaments a few to many cells long, discrete or pseudoparenchymatous, and bearing reproductive organs laterally or in conceptacles

3

2. Thallus minute, 0.5–5 mm across, epiphytic, with a monostromatic (occasionally distromatic in some genera) basal layer of radiating filaments, each cell of which produces a short (3–10 celled), free, simple or slightly branched, erect filament, or a hair or a reproductive organ

MYRIONEMATACEAE

2. Thallus usually 0.5–4 (–10) cm across, circular or irregularly spreading, epilithic or on solid substrates, with a monostromatic (or becoming polystromatic) basal layer of radiating filaments, with each upper cell producing one or two erect, simple or slightly branched filaments (usually 8–20 cells long) bearing terminal, lateral or intercalary reproductive organs

RALFSIACEAE

3. Thallus tufted, globose or pulvinate, with the cortical filaments continuing in the direction of the medullary filaments

4

3. Thallus erect, simple or (usually) much branched, with the cortical filaments more or less at right angles to the medullary filaments

5

4. Thallus 2–15 mm high, epiphytic, pulvinate or tufted, composed of short, erect, free filaments forming a medulla giving rise to a cortex with two types of filaments, shorter determinate ones and longer indeterminate ones; phaeophycean hairs absent

ELACHISTACEAE

4. Thallus globose or prostrate, pulvinate or convoluted, epiphytic or epilithic, gelatinous with filaments enclosed in mucilage; cortex with one type of filament; phaeophycean hairs present

LEATHESIACEAE

5. Growth subapical, by few to numerous, discrete, usually trichothallic filaments at apex of branches, with lateral filaments arising from subapical cells; cortical filaments not compacted (except in Chordaria); hairs single and scattered, arising from outer medullary or inner cortical cells; reproductive organs (unilocular or plurilocular) scattered, borne laterally from near the base or from the upper cells of the cortical filaments

CHORDARIACEAE

5. Growth apical, by one to numerous apical cells not surmounted by filaments, undergoing periclinal divisions to form filaments and dividing by anticlinal or oblique divisions to form lateral filaments; cortical filaments free or, usually, compacted laterally and pseudo-parenchymatous; reproductive organs (unilocular sporangia) formed from enlarged cortical cells, or cut off laterally from lower cells of cortical filaments, or formed in conceptacles

6

6. Thallus slender, much branched, with either one or 4–5 central filaments each arising from a slightly protruding apical cell; cortical assimilatory filaments either long, or reduced to tufts, or rudimentary, in each case free; phaeoplasts discoid

SPERMATOCHNACEAE

6. Thallus with simple, clavate, vesicles, or much branched, coarse to moderately slender, multiaxial with a convex to concave apex of numerous dividing apical cells (with single, larger, pyriform "apical" cells in Splachnidium); phaeophycean hairs clustered into depressions (cryptostomata) or conceptacles; phaeoplasts discoid or stellate

7

7. Thallus developing from a group of apical filaments, either in a convex apex or at the base of a hair group in an apical depression, producing a multiaxial thallus; phaeophycean hairs clustered in shallow depressions or in cryptostomata; phaeoplasts discoid or stellate; unilocular sporangia borne amongst cortical cells in vague but usually extensive surface sori

SCYTOTHAMNACEAE

7. Thallus with discrete, inactive, pyriform cells at the apex of branches and in conceptacles, surrounded by filaments with apical cells which divide anticlinally and below periclinally; short, clavate, 4–8 celled hairs present on cortical cells near branch apices, phaeophycean hairs present in conceptacles; phaeoplasts stellate; sporangia borne in conceptacles

SPLACHNIDIACEAE


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