Electronic Flora of South Australia Family Fact Sheet

ORDER DICTYOSIPHONALES Setchell & Gardner

Phylum Phaeophyta

Thallus (sporophyte) pulvinate and 1–10 mm high, or erect and 5–20 cm high, foliose or terete, solid or hollow, simple to much branched, with a small discoid holdfast. Growth diffuse (in some taxa trichothallic early), or apical but without a prominent apical cell. Structure polystichous, usually several cells thick, with a cortex of small, phaeoplastic cells and a medulla of (usually) larger, clearer, cells; or filamentous but with occasional longitudinal divisions; phaeophycean hairs usually present, single or clustered. Phaeoplasts discoid, several per cell, usually with a pyrenoid.

Reproduction: The sporophyte by unilocular sporangia (sometimes apomeiotic) or neutral plurilocular sporangia, borne within or on the cortex, usually in sori. Gametophytes (where known) with uniseriate gametangia and (usually) isogametes.

Life history diplohaplontic and heteromorphic, with the sporophyte macrothallic and the gametophyte microthallic; or direct from the sporophyte, often via filamentous microthalli.

Taxonomic notes: This order includes a heterogeneous assemblage of about 10 families (Wynne & Kraft 1981, p. 747), ranging from the minute pulvinate tufts of the Myriotrichiaceae to the foliose or inflated thalli of the Punctariaceae (including the filamentous Hecatonema). All members have polystichous thalli formed by intercalary longitudinal cell divisions, but they lack the internal and external thallus differentiation of the Laminariales, and they differ from the Scytosiphonales in life history and in having several phaeoplasts in each cell.

Variations in the life history of members of the Dictyosiphonales are described by Wynne & Loiseaux (1976, pp. 442, 443) and by Pedersen (1984), who discuss the many taxa which depart from an alternation of sporophytic macrothallus and gametophytic microthallus by having apomeiotic unilocular sporangia and direct development of the macrothallus. Culture studies to follow the reproductive cycles are essential, and some genera (such as Hecatonema and Streblonema) have been shown to be stages in the life history of Dictyosiphonales such as Myriotrichia (Loiseaux 1969, Pedersen 1978), Punctaria (Clayton & Ducker 1970), and of various Punctariaceae (Pedersen 1984, p. 58). Temperature, light and salinity can all affect the form of the thallus.

While some authors (e.g. Kylin 1933, p. 93; Fritsch 1945, p. 140; Bold & Wynne 1985, p. 341) have placed the Dictyosiphonales as a relatively advanced group, others (e.g. Christensen 1980, p. 126; Pedersen 1984, p. 47) have considered the order as relatively primitive, with the family Pogotrichaceae providing a link to members of the class Chrysophyceae of the Chrysophyta.

References:

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

CHRISTENSEN, T. (1980). Algae. A taxonomic survey. Fasc. 1 (Tryk: Odense.)

CLAYTON, M.N. & DUCKER, S.C. (1970). The life history of Punctaria latifolia Greville (Phaeophyta) in southern Australia. Aust. J. Bot. 18, 293–300.

FRITSCH, F.E. (1945). The structure and reproduction of the Algae. Vol. II. (Univ. Press: Cambridge.)

KYLIN, H. (1933). Über die Entwicklungsgeschichte der Phaeophyceen. Acta Univ. lund. N.F. Avd. 2, 29(7), 1–102, Plates 1, 2.

LOISEAUX, S. (1969). Sur une espèce de Myriotrichia obtenue en culture à partir de zoides d'Hecatonema maculans Sauv. Phycologia 8, 11–15.

PEDERSEN, P.M. (1978). Culture studies in the pleomorphic brown alga Myriotrichia clavaeformis (Dictyosiphonales, Myriotrichiaceae). Norw. J. Bot. 25, 281–291.

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

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.

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 DICTYOSIPHONALES

1. Thallus less than 1 cm high, with terete, solid, erect axes less than 200 µm and only a few cells in diameter

2

1. Thallus usually 5–50 cm high and 1 mm-10 cm broad, terete or complanate, solid or hollow; or minute, branched tufts with largely uniseriate but occasionally biseriate filaments (Hecatonema)

3

2. Thallus of basal filaments and erect, uniseriate but becoming multiseriate, filaments, with intercalary growth, and exerted, opposite, whorled or clustered, unilocular or plurilocular sporangia

MYRIOTRICHIACEAE

2. Thallus pulvinate, with a basal disc of radiating filaments, producing (with or without a medulla) numerous erect, multiseriate axes each with a uniseriate base, meristematic at the base or near the apex; plurilocular organs of three kinds, basal pedicellate ones and lateral or intercalary ones on the axes

GIRAUDIACEAE

3. Thallus slender, cylindrical, usually branched and solid or becoming hollow, with a long, uniseriate, terminal filament before longitudinal cell divisions occur

STRIARIACEAE

3. Thallus simple, complanate and solid or hollow, or terete, inflated and hollow; growth initially trichothallic, soon becoming diffuse, with longitudinal cell divisions occurring within a few cells of the apices; or minute branched tufts with largely uniseriate but occasionally biseriate filaments

PUNCTARIACEAE


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