Electronic Flora of South Australia Genus Fact Sheet

Genus BRYOPSIS Lamouroux 1809: 133

Phylum Chlorophyta – Order Derbesiales – Family Bryopsidaceae

Thallus diplohaplontic, heteromorphic, with a much branched gametophyte and small, slightly branched sporophyte. Gametophyte erect, with one or more percurrent axes arising from branched rhizoids; axes radially, bilaterally or pinnately branched, with the laterals in most species becoming similarly branched, with the ultimate branchlets (the ramuli) elongate and cylindrical or terete, often lost from lower parts of the axes and laterals, leaving scars which may disappear below; chloroplasts numerous, discoid to lenticular, with a usually conspicuous pyrenoid. Sporophyte minute, slightly and irregularly branched.

Reproduction: Gametophytes monoecious or dioecious, anisogamous; ramuli cut off by a basal septum to form unisexual or bisexual gametangia. Sporophyte producing stephanokontic zoospores within the filaments.

Lectotype species: B. pennata Lamouroux.

Taxonomic notes: Numerous species of Brvopsis have been described, especially from the Mediterranean, but their variability and specific limits are often uncertain. Culture and life-history studies such as those of Rietema (1975) are essential to understanding the species, and these have only been attempted for Australian species by MacRaild (1974, unpublished). Considerable variation occurs in the branching patterns of some species, due in part to ecological factors and also to their growth habit, and in some areas it seems likely that intergrades between species also occur with gene exchange. Thus some species (e.g. B. foliosa) are typically radially branched throughout but lower parts of axes may show bilateral arrangement of ramuli or laterals. Other species (e.g. B. australis) may have largely unilateral ramuli when growing in dense tufts rather than the typical bilateral arrangement of two irregular rows on each side. This type of variation, from radial in some (usually upper) parts to bilateral with either two alternating rows on each side or an irregular grouping on the opposite sides is often puzzling and needs to be studied from ecological and developmental viewpoints and in culture.

In Europe, B. plumosa has been shown to be dioecious, while B. hypnoides is monoecious with both male and female gametes in the one gametangium, and B. monoica is also monoecious but the male and female gametes are produced in separate gametangia. MacRaild (1974) has shown that in southern Australia, B. plumosa, B. vestita and B. gemellipara are all dioecious and the diploid microthalli produce stephanokontic zoospores.

Naming and characterisation of the southern Australian species must remain tentative until both further knowledge is available on European species and life-history and ecological studies on Australian species have been carried out. The following key and descriptions are based essentially on morphological features.

References:

LAMOUROUX, J.V.F. (1809). Mémoire sur trois nouveaux genres de la famille des Algues marines. J. de Bot. 2, 129–135.

MacRAILD, G.N. (1974). The taxonomy, life history and cytology of Bryopsis and related genera from southern Australia. (Ph.D. thesis, Univ. Melbourne.)

RIETEMA, H. (1975). Comparative investigations on the life-histories and reproduction of some species in the siphoneous green algal genera Bryopsis and Derbesia. (Univ. Groningen.)

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 SPECIES OF BRYOPSIS

1. Thallus essentially radially branched

2

1. Thallus distichously branched, or bilaterally (occasionally unilaterally) branched in double rows, at least in some parts of the thallus

5

2. Ramuli slender, (12–) 20–55 µ in diameter, irregularly and sparsely to profusely radially branched 1

B. minor

2. Ramuli stouter, mostly over 70 µm in diameter, laterals usually densely branched

3

3. Thallus delicate, with slender, usually simple, axes (2–) 3–6 (–8) cm high, bearing ramuli (which become laterals) separated by two to several times their basal width

B. macraildii

3. Thallus robust, densely branched, axes often over 8 cm high, strongly developed or with irregular long laterals, with ramuli on upper parts usually separated by less than twice their basal width •

4

4. Thallus 4–10 (–15) cm high, axes usually with irregularly placed long laterals above; ramuli very dense, usually covering the axes or laterals, slightly curved, 0.5–1 mm long when mature, usually radially arranged but sometimes more or less bilaterally arranged in plants epiphytic on seagrasses

B. foliosa

4. Thallus tufted, usually 5–15 (–25) cm high, with numerous erect axes from a matted base, usually without long irregular laterals but densely covered with ramuli which develop into short laterals (mostly 0.5–1 cm long) bearing ramuli; ramuli 0.5–2 (–3) mm long, straight to slightly curved

B. vestita

5. Thallus distichously branched, with ramuli mostly lying in single rows on each side, often more irregular lower on axes

B. plumosa

5. Thallus mostly bilaterally branched (or radially near apices), with ramuli or laterals on each side mainly in two slightly displaced rows, occasionally mostly unilateral

6

6. Thallus 2–4 (–5) cm high, usually in tufts of 8–30 axes, axes usually less than 0.5 mm in diameter, ramuli mainly bilaterally arranged (or unilaterally in dense tufts)

B. australis

6. Thallus 5–15 (–20) cm high, robust, epiphytic, with 1 to a few strongly developed axes (0.5–) 1–1.5 mm in diameter, laterals and ramuli bilaterally arranged except for frequent radial arrangement near apices, scars prominent

B. gemellipara


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