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Electronic Flora of South Australia Genus Fact Sheet

Genus CERAMIUM Roth 1797: 146, nom. cons.

Phylum Rhodophyta – Order Ceramiales – Family Ceramiaceae – Tribe Ceramieae

Thallus prostrate or (usually) erect, complanately or irregularly much branched, or with simple erect branches, branching alternate to subdichotomous, adventitious in some species, apices straight or involute; branches terete or compressed with nodal cortication from periaxial cells; attachment by unicellular or multicellular rhizoids, usually with digitate pads.

Structure. Apical cells dividing obliquely, lateral branches arising by oblique division of subapical cell and developing as strongly (hence subdichotomous) or less strongly (hence alternate) as the parent axis. Subapical cells cutting off 3–10 periaxial cells in alternating sequence (dividing laterally to form pseudoperiaxial cells in some species), and producing chains of cells acropetally and usually basipetally, which adhere closely to the adjacent cells, leaving a clear space on the axial cell or closing this space largely or completely; some species forming an outer cortex of small cells; short spinous laterals from the cortical cells present in some species, hairs common, and some species forming gland cells in the cortex; axial cells usually much larger than periaxial or cortical cells, usually with a prominent central protoplasmic strand between the pit-connections. Cells uninucleate.

Reproduction: Gametophytes dioecious, rarely monoecious. Procarps formed on the first periaxial cell, often in a short row, with a sterile group and a 4-celled carpogonial branch; post-fertilization the auxiliary cell divides to a foot cell and gonimoblast initial producing one to several successive gonimolobes, all cells becoming carposporangia, with the foot cell, supporting residual cell and axial cell fusing; carposporophytes naked, often partly involucrate by lateral branches from below. Spermatangia formed in extensive sori on the nodal cortices, with initials cutting off 1–3 spermatangia.

Tetrasporangia formed from the periaxial or cortical cells, naked or partly involucrate by short branchlets, usually tetrahedrally divided.

Type species: C. rubrum C. Agardh 1811: 17 (nom. cons. prop. Silva et al. 1996: 403).

Taxonomic notes: A widespread genus of many species, with 15 recorded for southern Australia by Womersley (1978). Other species also occur in this region but are inadequately known. These include one provisionally referred to as C. wilsonii in Womersley (1978, p. 206), known only from tetrasporangial specimens of J.B. Wilson from Port Phillip Heads and Western Port, Victoria (MEL, 45466, 45467), and also a minute species of the C. codii group from Twin Rocks, Head of the Great Australian Bight, S. Aust., growing on Amphiroa anceps, 20–22 m deep (Branden, 19.i.1991; AD, A61152). This sterile collection has prostrate filaments with simple, straight, erect branches, nodes with 5 periaxial cells and only acropetal [1 (–2)] cortical cells, with filaments 35–45 in diameter and axial cells L/D (1–) 1.2–1.8.


AGARDH, C.A. (1811). Dispositio Algarum Sueciae. pp. 17–26. (Berling: Lund.)

ROTH, A.G. (1797). Catlecta botanica quibus plantae novae et minus cognitae describunter atque illustrantur. Fasc. 1. (Lipsiae.)

SILVA, P.C., BASSON, P.W. & MOE, R.L. (1996). Catalogue of the Benthic Marine Algae of the Indian Ocean. (University of California Press: Berkeley, Los Angeles & London.)

WOMERSLEY, H.B.S. (1978). Southern Australian species of Ceramium Roth (Rhodophyta). Aust. J. Mar. Freshw. Res. 29, 205–257.

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

Author: H.B.S. Womersley

Publication: Womersley, H.B.S. (24 December, 1998)
The Marine Benthic Flora of Southern Australia
Rhodophyta. Part IIIC. Ceramiales – Ceramiaceae, Dasyaceae
©State Herbarium of South Australia, Government of South Australia


1. Cortical cells near the apices, and in some species in older parts, bearing short, spinous or tapering filaments 1–7 cells long, with cells much narrower than the axial cells.


1. Cortical cells not bearing spinous or tapering filaments (excluding slender caducous hairs)


2. Cortical band normally 2 cells long in all parts, with many of the cells bearing slender filaments 2–7 cells long as a double whorl at each node; terminal cells of filaments rounded or forming a hair

C. shepherdii

2. Cortical band more than two cells long, bearing acute spines at least near the branch apices, but not in whorls


3. Spines single at each node, abaxial, 3–6 cells long, relatively coarse; internodal space present throughout thallus; tetrasporangia partly to largely involucrate; usually epiphytic on Codium fragile or Corallina

C. monacanthum

3. Spines one to several per node near apices, to 4 cells long, relatively slender; cortical cells on older branches with numerous 1–3-celled spines; internodal space present on young branches, closing on older parts; tetrasporangia mostly abaxial, largely enveloped by small cells; usually epiphytic on seagrasses (Posidonia, sometimes Amphibolis)

C. puberulum

4. Cortication complete except possibly within a few axial cells of the apices; outer cortex present; tetrasporangia enveloped (or almost so) within the cortex


4. Cortical bands short to relatively long, separated by a clear (though sometimes narrow) internodal space in at least the upper part of the thallus; outer cortex present or absent; tetrasporangia usually protruding, naked or involucrate


5. Branching usually subdichotomous, without alternate flabellate laterals; cortical cells becoming elongate and dovetailing to give complete cortication within 6–8 axial cells from apices; rosettes of outer cortical cells present around periaxial cells; older inner cortical cells usually L/D 3–5, usually without distinct rosettes of outer cells; tetrasporangia formed first from periaxial cells, later formed from cortical cells near nodes and thus more irregularly scattered; usually occurring in sheltered water

C. rubrum

5. Main axes bearing alternate, flabellate, lateral branch systems; cortical cells isodiametric, remaining ovoid to subspherical (L/D usually less than 2) often with well-defined rosettes of outer cells; young inner cortical cells smaller acropetally than basipetally, with this distinction often visible for many segments from apices; tetrasporangia usually in a well-defined ring at each node, mostly cut off from periaxial cells; epiphytic and usually occurring under strong water movement

C. pusillum

6. Thallus relatively robust with the cortical bands becoming 8 or more cells long; branching alternate to irregularly lateral, often with proliferous branchlets, becoming 300 µm or more thick in older branches; internodal spaces present or closed on older branches; tetrasporangia becoming whorled, largely involucrate, formed in branchlets which often become stichidiose


6. Thallus either moderately robust and usually strictly dichotomous, usually without laterals and over 200 µm thick below, or relatively slender (usually less than 200 µm thick) and more irregularly branched; cortical bands normally less than 8 cells long (except in older nodes of C. flaccidum), with internodal spaces present throughout thallus; tetrasporangia naked or involucrate


7. Thallus complanately branched, alternately branched every (3–) 4–5 cells; internodal space narrow and lenticular in face view of branches, cortication closing in older parts; outer cortex usually absent or slight

C. lenticulare

7. Thallus complanately or irregularly branched; internodal space uniform around the node, distinct at least in younger branches; outer cortex well developed on older branches


8. Thallus complanately branched above; periaxial cells (7–) 8; internodal space usually very narrow forming an annular ring, cortical cell divisions synchronous with the space closing completely on older branches; outer cortex present on older axes as rosettes around the periaxial cells and later from the inner cortical cells, mainly covering the central part of the nodal cortication

C. excellens

8. Thallus irregularly branched (not complanate); periaxial cells usually 7–8; internodal space usually 0.5–1 times as long as cortical band, normally remaining as a narrow gap on older axes; cortical cell divisions at first synchronous, later extending irregularly; outer cortex present in branchlets, becoming extensive over periaxial and inner cortical cells

C. tasmanicum

9. Thallus over 200 µm thick below, usually strictly dichotomous, fastigiate; tetrasporangia naked or very slightly involucrate


9. Thallus rarely over 200 µm thick, irregularly subdichotomous to laterally branched; tetrasporangia with a slight to extensive involucre


10. Periaxial cells 7–8 (–9), each cutting off two cells both acropetally and basipetally; gland cells usually present; outer cortex present on older parts; tetrasporangia naked, produced from periaxial or cortical cells at first as a ring around upper end of node, later scattered

C. isogonum

10. Periaxial cells 6–7, each cutting off laterally two pseudoperiaxial cells thus forming a ring of 18–21 cells at the node, from which cortical cells develop acropetally and basipetally; gland cells occasionally present; outer cortex absent; tetrasporangia slightly involucrate, produced from the true periaxial cells, at first abaxially and later around the node

C. australe

11. Cortical cells developing acropetally only (rarely single basipetal cells) from the periaxial cells


11. Cortical cells developing acropetally and basipetally (rarely few in C. cliftonianum) from the periaxial cells


12. Periaxial cells producing acropetally branched chains of 4–5 cortical cells, progressively smaller, forming a cupulate node; tetrasporangia becoming verticillate

C. cupulatum

12. Periaxial cells each cutting off laterally a wedge-shaped pseudoperiaxial cell which largely interposes in the periaxial ring (then of 10–12 cells), each then cutting off 1 or 2 cells acropetally giving a node 2–3 cells long; basipetal cells rare; tetrasporangia abaxial

C. macilentum

13. Periaxial cells each cutting off two cells acropetally but only a single laterally elongate cell basipetally; the latter may cut off a further single cell, or 2 cells, and may itself divide laterally into 2–4 smaller cells; tetrasporangia whorled, largely involucrate; rhizoids unicellular

C. flaccidum

13. Periaxial cells each cutting off 2 (–3) isodiametric cells acropetally and usually basipetally; tetrasporangia opposite and largely involucrate, or unilateral and partly involucrate; rhizoids uniseriate-celled with multicellular pads


14. Thallus epiphytic on larger brown algae, with prostrate filaments attached by clumps of rhizoids, and erect complanate branches; branching alternate, normally every 3 cells; internodal spaces about as long (to twice) as cortical bands; tetrasporangia essentially opposite in plane of branching, largely involucrate

C. filiculum

14. Thallus epilithic, epiphytic or epizoic, irregularly branched, subcomplanate above, branched at intervals of 4 or more axial cells; internodal spaces usually becoming several times as long as cortical bands; tetrasporangia unilateral and abaxial, partly involucrate

C. cliftonianum

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