Electronic Flora of South Australia Genus Fact Sheet

Genus RHIZOCLONIUM Kützing 1843: 261

Phylum Chlorophyta – Order Cladophorales – Family Cladophoraceae

Thallus of slender (10–45 µm in diameter) filaments forming entangled masses, unbranched apart from occasional to frequent, short, lateral rhizoidal branches. Cells cylindrical, L/B usually 1–8, with 1–4 nuclei and a parietal, reticulate (loose to dense) chloroplast with few to several pyrenoids.

Reproduction: Reproduction by biflagellate isogametes and quadriflagellate zoospores, diplohaplontic with isomorphic generations (not recorded for Australian material).

Type species: R. jürgensii Kützing (= R. riparium (Roth) Harvey 1849: pl. 238). See Koster 1955, p. 341.

Taxonomic notes: The Australian species of Rhizoclonium need detailed revision, from living field material and culture studies. They are not uncommon in mangrove communities and other shaded, intertidal habitats in calm bays and inlets, forming mats or felts on the substrate or on the lower parts of mangroves. Four species are recognised below, but others may well occur. R. riparium and R. implexum are usually recognised as distinct species but some authors (e.g. Nienhuis 1974) include the latter under R. riparium.

Some species of Rhizoclonium have been placed in Lola Hamel & Hamel by Chapman (1956, p. 463) and Zaneveld (1966, p. 47). Lola is based on R. lubricum Setchell & Gardner and is distinguished by its sexual reproduction by anisogametes. The nature of the gametes of other species appears not to have been described and Lola is used by Chapman (1956, p. 462) as a borderline genus between Chaetomorpha and Rhizoclonium. It seems best, as most authors have done, not to recognise Lola but place the slenderer species (often with lateral rhizoids) in Rhizoclonium and broader species (without such rhizoids) in Chaetomorpha.

References:

CHAPMAN, V.J. (1956). The marine algae of New Zealand. Part I. Myxophyceae and Chlorophyceae. J. Linn. Soc. Bot. 55 (360), 333–501, Plates 24–50.

HARVEY, W.H. (1849). Phycologia Britannica. Plates 217–252 (Reeve: London.)

KÜTZING, F.T. (1843). Phycologia generalis. (Leipzig.)

KOSTER, J.Th. (1955). The genus Rhizoclonium Kutz. in the Netherlands. Pubbl. Staz. Zool. Napoli. 27, 335–357.

NIENHUIS, P.H. (1974). Variability in the life cycle of Rhizoclonium riparium (Roth) Harv. (Chlorophyceae: Cladophorales) under Dutch estuarine conditions. Hydrobiol. Bull. 8, 172–178.

ZANEVELD, J.S. (1966). Lola irregularis (Chlorophyta-Cladophoraceae): A new species from the Ross Sea, Antarctica. J. Phycol. 2, 45–47.

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 RHIZOCLONIUM

1. Cells of filaments usually L/B 2 or greater, rhizoids absent or occasional

2

1. Cells of filaments usually L/B less than 2, rhizoids occasional to frequent

3

2. Filaments usually 16–22 µm in diameter, cells L/B 2–6

L R. implexum

2. Filaments usually 25–45 µm in diameter, cells L/B mostly 2–3

R. tortuosum

3. Filaments straight to irregularly curved, rhizoids irregularly placed, filament diameter 16–22 µm

R. riparium

3. Filaments regularly curved between rhizoids at more or less regular intervals, filament diameter 24–32 µm

R. curvatum


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