Electronic Flora of South Australia Family Fact Sheet

ORDER ECTOCARPALES Setchell & Gardner

Phylum Phaeophyta

Thallus of loose tufts or strands a few mm to 25 cm long, of free, uniseriate, branched filaments, or occasionally endophytic, heterotrichous, attached by basal rhizoids, sometimes free-floating. Growth diffuse or largely restricted to near the base of branches, rarely apical. Phaeoplasts elongate (ribbon-like) or discoid and numerous, parietal or axile, with one (if discoid) to a few pyrenoids.

Reproduction: The sporophyte by unilocular (usually meio) sporangia and by neutral plurilocular sporangia. The gametophyte by plurilocular gametangia with iso- or anisogametes, sometimes parthenogenetic.

Life history diplohaplontic with essentially isomorphic generations, or direct.

Taxonomic notes: This order is recognised here in a restricted sense, including only the free-filamentous taxa with strands or tufts of uniseriate filaments. Thus the crustose Ralfsiales are excluded, as are the haplostichous Chordariales and some other orders which certain authors include in a very broad Ectocarpales (e.g. Fritsch 1945; Russell & Fletcher 1975; Clayton 1981a). Some simple taxa (e.g. Compsonema, Hecatonema) which show longitudinal segmentation of either basal or erect-system cells are placed in the Dictyosiphonales, but the significance of such longitudinal divisions is doubtful.

The limits of currently recognised genera are often uncertain, due in part to the frequency of pleiomorphy in their life histories (Wynne 1981, p. 67) and in part to the likelihood that some are stages in the life history of other taxa (Ravanko 1970; Bold & Wynne 1978, p. 275). Further studies will probably show that some genera cannot be maintained, and Russell & Garbary (1978) in a numerical analysis of the British species suggest that all should be placed in the genus Ectocarpus. This would mean abandonment of some 16 genera, including Giffordia and Feldmannia. However, Russell & Garbary did not present a key to the taxa they would recognise under Ectocarpus and such a key may well recognise subgeneric groups corresponding to some of the currently recognised genera. Ravanko (1970, p. 179) suggests that "only a few true species ... exist in the Ectocarpales" and that most genera represent only developmental stages under particular environmental conditions. Most authors seem unwilling to accept this until species are more clearly related to others and synonymies established.

The genera recognised below follow largely the account of Clayton (1974) of southern Australian species, while recognising that life-history studies are still necessary on most taxa.

In the restricted Ectocarpales used here, all the following genera are placed in a single family, Ectocarpaceae, with the characteristics of the order. Pedersen (1984, p. 50) however has removed Pilayella, Bachelotia and Zosterocarpus to a separate family, Pilayellaceae, characterised by occasional longitudinal cell divisions, by sporangia formed by transformation of vegetative cells, and by pseudostreblonematoid fertile microthalli.

References:

BOLD, H.C. & WYNNE, M.J. (1978). Introduction to the Algae: Structure and reproduction. (Prentice-Hall: New Jersey.)

CLAYTON, M.N. (1974). Studies on the development, life history and taxonomy of the Ectocarpales (Phaeophyta) in southern Australia. Aust. J. Bot. 22, 743–813.

CLAYTON, M.N. (1981a). Phaeophyta. In Clayton, M.N. & King, R.J. (Eds), Marine Botany: an Australasian Perspective, Ch. 5, pp. 104–137. (Longman Cheshire: Melbourne.)

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

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

RAVANKO, O. (1970). Morphological, developmental and taxonomic studies in the Ectocarpus complex (Phaeophyceae). Nova Hedwigia 20, 179–252.

RUSSELL, G. & FLETCHER, R.L. (1975). A numerical taxonomic study of the British Phaeophyta. J. mar. biol. Ass. U.K. 55, 763–783.

RUSSELL, G. & GARBARY, D. (1978). Generic circumscription in the family Ectocarpaceae (Phaeophyceae). J. mar. biol. Ass. U.K. 58, 517–525.

WYNNE, M.J. (1981). Phaeophyta: Morphology and classification. In Lobban, C.S. & Wynne, M.J. (Eds), The Biology of Seaweeds, Ch. 2, pp. 52–85. Bot. Monogr. Vol. 17. (Blackwell: Oxford.)

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 ECTOCARPACEAE

1. Growth apical, apical cells cylindrical, of similar diameter to lower cells

ASTERONEMA

1. Growth intercalary, diffuse or in meristematic regions along the filaments, occasionally also apical with narrower, tapering, apical cells

2

2. Phaeoplasts elongate, aggregated into one or two central stellate clusters in each cell; sporangia intercalary

BACHELOTIA

2. Phaeoplasts elongate or discoid, parietal, numerous and scattered in each cell: sporangia lateral or terminal (intercalary in Pilayella)

 3

3. Phaeoplasts elongate (ribbon shaped), each with several pyrenoids

4

3. Phaeoplasts discoid or ovoid, rarely slightly elongate (L/B* 2–3 (–5), each with usually one pyrenoid

5

4. Phaeophycean hairs (with a basal meristem) present; sporangia usually sessile; lower filaments 50–90 µm in diameter

KUCKUCKIA

4. Phaeophycean hairs absent, though tapering branch ends often hair-like; sporangia usually pedicellate; lower filaments 20–45 µm in diameter

ECTOCARPUS

5. Thallus a few mm to several cm long, tufted

6

5. Thallus minute, forming microscopic clusters of filaments, epiphytic or partly endophytic

11

6. Filaments with a conical dividing apical cell, without hairs of any kind, plurilocular sporangia surrounding the cells of a branch

ZOSTEROCARPUS

6. Filaments with diffuse or regional growth, usually tapering to a terminal phaeophycean or false hair, plurilocular sporangia lateral or intercalary

7

7. Sporangia grouped into irregular, lobed, lateral sori; phaeophycean hairs present, frequently terminal

SOROCARPUS

7. Sporangia discrete, ovoid to elongate; phaeophycean hairs absent, false hairs often present

8

8. Plurilocular and unilocular sporangia intercalary

PILAYELLA

8. Plurilocular and unilocular sporangia lateral or terminal

9

9. Meristematic zones usually at the base of long, unbranched filaments; sporangia mostly pedicellate

FELDMANNIA

9. Meristems scattered, often at the base of relatively short laterals, or inconspicuous; sporangia mostly sessile

10

10. Short 2–4 celled lateral filaments frequent; stolon-like filaments common; reproduction by plurilocular organs with either large or small loculi, by unilocular sporangia and by monosporangia

ACINETOSPORA

10. Short lateral filaments absent (except in G. sordida); stolon-like filaments rare or absent; reproduction by plurilocular sporangia and by occasional unilocular sporangia

GIFFORDIA

11. Thallus with basal filaments either separate or aggregated on host surface, with short, erect, simple or sparsely branched filaments, without phaeophycean hairs

KUETZINGIELLA

11. Thallus largely endophytic or as elachistoid tufts, with endophytic base, with or without phaeophycean hairs

12

12. Thallus largely endophytic with basal filaments penetrating the host, and a few to a tuft of short, erect, branched filaments projecting from the host and bearing uniseriate or multiseriate plurilocular sporangia; phaeophycean hairs present or absent

STREBLONEMA

12. Thallus of elachistoid tufts to 2 mm high, epiphytic in cryptostomata of Adenocystis, with elongate, basal plurilocular organs and phaeophycean hairs

GONONEMA


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