Electronic Flora of South Australia Family Fact Sheet

Phylum CHLOROPHYTA Pascher

Thallus microscopic or macroscopic and up to about 60 cm long, free or attached, light to dark green or slightly yellowish green with chlorophylls a and b, (I carotene and lutein and other xanthophylls, contained in chloroplasts of varied form but with bands of 2–6 thylakoids and usually with one to several pyrenoids, with starch as the storage reserve. Habit varying from small uninucleate unicells to colonies, filaments, foliose or tubular forms; or of larger multinucleate cells forming unbranched or branched filaments or nets; or coenocytic with no or occasional cross walls, either forming elaborate and variously branched thalli, or consisting of slender filaments entangled or compacted to form macroscopic, branched thalli. Growth intercalary or diffuse, occasionally apical. Cells with one to several chloroplasts, central or parietal, usually numerous and discoid in larger taxa. Nuclear division phragmoplastic or phycoplastic. Cell wall rigid, usually of cellulose microfibrils, in some groups of xylan or mannan, in a few taxa calcified.

Reproduction: Reproduction usually by isogametes or anisogametes, occasionally by oogametes, or by amoeboid gametes; and by motile zoospores, aplanospores or akinetes. Motile zooids with two or four apical flagella of equal length (isokont) or a subapical ring of numerous flagella (stephanokontic), without hairs on the flagella.

Life history haplontic* (i.e. thallus haploid or gametophytic, with meiosis at the first division of the zygote nucleus), diplontic (i.e. thallus diploid with meiosis at gametogenesis) or diplohaplontic with distinct gametophyte and sporophyte generations (isomorphic or heteromorphic).
* These terms are distinct from haplobiontic and diplobiontic, which refer to organisms with one or two generations in their life history.

Taxonomic notes: Algae of the Chlorophyta are usually readily recognised by their colour and morphology. They occur in both fresh and marine waters, in the soil and in moist land situations (e.g. on bark of trees). Marine forms range from motile or non-motile phytoplankton cells to small epiphytic forms, and to larger benthic taxa. Most of the latter are attached to rock, but some grow anchored in mud or epiphytic on seagrasses or other algae.

This account deals only with the attached, benthic or epiphytic Chlorophyta, and does not attempt to cover the planktonic taxa which have not been investigated in South Australian seas. These motile unicells are placed in the Classes Prasinophyceae or Chlorophyceae, and Parke & Dixon (1976) recorded some 17 unicellular genera and 73 species of the former class, and 8 unicellular genera and 55 species of the latter class from Britain. There are probably several taxa in southern Australian waters.

The classification of the Chlorophyta used here is essentially that of Round (1971), which was adopted by MacRaild (1981). Reference should be made to Round and also to Bold & Wynne (1978) for a general discussion of the Chlorophyta and for orders not represented in the southern Australian benthic marine flora. Considerable changes in classification of the Chlorophyta have occurred in recent years, particularly as ultrastructural and biochemical knowledge (i.e. of nuclear division and cell wall structure) has developed, and it will probably be some time before any one classification is generally accepted. Van den Hoek (1981) reviewed the value of morphological, life history and ultrastructural features in the classification of the Chlorophyta, and Tanner (1981) discussed life histories and their variations in the orders of this phylum.

As knowledge has developed, there has been a strong tendency to elevate family groups to the rank of orders (e.g. Round 1971). Whereas some years ago the Chlorophyta were considered to include only one class, the Chlorophyceae (e.g. Papenfuss 1955, Bold & Wynne 1978), other authors (e.g. Parke & Dixon 1976) have recognised a second class, the Prasinophyceae. Round (1971) separated the latter group as a phylum, Prasinophyta, and grouped his 33 orders of the Chlorophyta as four classes, of which two (Bryopsidophyceae and Chlorophyceae) have marine representatives. However, van den Hoek (1981, p. 122) considers the class Prasinophyceae not to be justified, and comments on the bases for recognition of orders and classes in the Chlorophyta. Kornmann (1973) has since added the class Codiolophyceae for taxa with a heteromorphic life history involving a unicellular sporophyte and Christensen (1962) recognised several other classes. Stewart & Mattox (1978) placed Ulva and its relatives in the Class Ulvophyceae. A catalogue of the class and family names used in the Chlorophyta has been given by Silva (1980).

The account below of the Chlorophyta is based on orders, of which the Ulotrichales would be placed in the Class Codiolophyceae, coenocytic orders (Cladophorales to Caulerpales) in the Bryopsidophyceae, and the remaining uninucleate celled orders in the Chlorophyceae.

The larger benthic Chlorophyta of southern Australian coasts are now generally well known, though other species may well be found, especially in deep water collections. The remarkable Palmoclathrus (see below) shows that unusual taxa are still to be discovered. The small, often epiphytic or shell-boring taxa of the Ulotrichales and Chaetophorales are, however, far from adequately known and no doubt other genera will be recorded from our coasts. While the general morphology of most southern Australian Chlorophyta may be known, there are few records (and almost none in detail) of their reproduction and life history. For most widely distributed species (e.g. in the genera Cladophora, Chaetomorpha, and Ulothrix), the information on the reproduction of the species is based largely on Northern Hemisphere studies.

References:

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

CHRISTENSEN, T. (1962). Alger. In Böcher, T.W., Lange, M. & Sorensen, T. (Eds), Systematisk Botanik, Vol. 2(2), 1–180. (Munksgaard: Copenhagen.)

KORNMANN, P. (1973). Codiolophyceae, a new class of Chlorophyta. Helgoländer wiss. Meeresunters. 25, 1–13.

MacRAILD, G.N. (1981). Chlorophyta. In Clayton, M. N. & King, R. J. (Eds), Marine Botany: An Australasian Perspective, Ch. 7, pp. 180–199. (Longman Cheshire: Melbourne.)

PAPENFUSS, G.F. (1955). Classification of the algae. In A century of progress in the natural sciences, 1853–1953. (Calif. Acad. Sci.: San Francisco.)

PARKE, M. & DIXON, P.S. (1976). Check-list of British marine algae-third revision. J. mar. biol. Ass. U.K. 56, 527–594.

ROUND, F.E. (1971). The taxonomy of the Chlorophyta. II. Br. phycol. J. 6, 235–264.

SILVA, P.C. (1980). Names of classes and families of living algae. Regnum vegetable 103, 1–156.

STEWART, K.D. & MATTOX, K.R. (1978). Structural evolution in the flagellated cells of green algae and land plants. Biosystems 10, 145–152.

TANNER, C.E. (1981). Chlorophyta: Life histories. In Lobban, C.S. & Wynne, M. J. (Eds), The Biology of Seaweeds, Ch 6, pp. 218–247. Botanical Monogr. Vol. 17. (Blackwell: Oxford.)

VAN DEN HOEK, C. (1981). Chlorophyta: Morphology and classification. In Lobban, C.S. & WYNNE, M.J. (Eds). "The Biology of Seaweeds", Ch. 3, pp. 86–132. Botanical Monogr. Vol. 17. (Blackwell: Oxford.)

The Marine Benthic Flora of Southern Australia Part I complete list of references.

Author: H.B.S. Womersley

Publication: Womersley, H.B.S. (31 May, 1984)
The Marine Benthic Flora of Southern Australia
Part I
©Board of the Botanic Gardens and State Herbarium, Government of South Australia

KEY TO ORDERS OF CHLOROPHYTA

1. Thallus consisting of minute uninucleate cells embedded without order in a gelatinous matrix, aggregated to form a stalked, cupulate, and clathrate thallus 5–15 cm high

Palmoclathrus (TETRASPORALES)

1. Thallus of small uninucleate cells, organised into filaments or foliose; or filaments of large multinucleate cells; or coenocytic and organised into thalli of various forms

2

2. Thallus of small, uninucleate cells usually less than 20 µm across, with a single chloroplast filling most or part of the cell, not perforate or reticulate; thallus filamentous or foliose

3

2. Thallus of large, multinucleate cells usually over 50 µm across (except Rhizoclonium and Urospora - 10–4511m in diameter), or coenocytic; chloroplasts discoid and numerous or reticulate

6

3. Thallus of uniseriate filaments, simple or branched

4

3. Thallus foliose or tubular, one or two cells thick; or of filaments 2 cells broad; or more or less terete, solid and 1–4 cells thick (uniseriate only in young stages)

5

4. Thallus (gametophyte) unbranched, of free filaments to 5 cm high; sporophyte unicellular and microscopic (Codiolum stage)

ULOTRICHALES

4. Thallus branched, usually less than 3 mm high, on or in the surface of larger algae (or shells)

CHAETOPHORALES

5. Thallus one or two cells thick or broad, usually over 1 cm high, chloroplast parietal, laminate (stellate in the tubular thalli of Blidingia); diplohaplontic and isomorphic; isogamous or anisogamous

ULVALES

5. Thallus foliose (not tubular) and one cell thick; or filamentous and 1 to a few cells thick, 2–10 mm high, chloroplast central and somewhat stellate; diplontic with gametic meiosis in upper thallus cells or haplontic; oogamous

PRASIOLALES

6. Thallus filamentous or reticulate, or a cupulate or flattened membrane, with regularly or occasionally irregularly positioned cross walls

7

6. Thallus filamentous (entangled or not); or of various macro forms; or with whorled organisation; in all cases without complete cross walls in the vegetative thallus

9

7. Thallus filamentous, simple or branched or reticulate, with regularly or irregularly placed cross walls forming large (small in Rhizoclonium and Urospora),usually multinucleate cells

8

7. Thallus a hollow sac opening to a cupulate or flattened thallus of large, multinucleate cells; new cells formed by segregative division within old cells

Dictyosphaeria (SIPHONOCLADALES)

8. Usually isomorphic; pores of zooidangia simple; cell wall of cellulose I microfibrils in crossed sets; chloroplasts numerous, discoid to angular, forming a parietal reticulum, containing bilenticular pyrenoids; cross wall formation independent of nuclear division

CLADOPHORALES

8. Usually heteromorphic, the sporophyte unicellular (Codiolum like); pores of zooidangia operculate or simple; cell wall with random microfibrils of cellulose II; chloroplasts continuous, parietal, perforate, containing polypyramidal pyrenoids; cross wall formation following division of many nuclei in plane of cell division

ACROSIPHONIALES

9. Thallus radially constructed, with a central axis bearing whorls of lateral branches; vegetative thallus uninucleate before reproduction; gametes formed in cysts or in gametangial rays

DASYCLADALES

9. Thallus not of radial and whorled construction; cysts not formed

10

10. Thallus diplohaplontic, heteromorphic; sporophyte filamentous, usually much branched, reproducing by stephanokontic zoospores; gametophyte an ovoid vesicle or filamentous, less than 1 cm long, anisogamous.

DERBESIALES

10. Thallus diplontic, either formed of slender filaments united (in most genera) into a macroscopic thallus, or morphologically differentiated into a basal stolon and erect fronds; reproduction by isogametes or anisogametes following meiosis

11

11. Thallus simple or branched, composed of densely entwined filaments forming a medulla and a cortex of utricles bearing gametangia laterally; homoplastic, chloroplasts only present; wall containing mannan

CODIALES

11. Thallus consisting either of entwined or associated filaments or of a basal stolon attached by rhizoids and with erect fronds of various forms; heteroplastic, chloroplasts and amyloplasts present; wall containing xylan

CAULERPALES


Disclaimer Copyright Disclaimer Email Contact:
State Herbarium of South Australia
Government of South Australia Government of South Australia Department of Environment, Water and Natural Resources