Electronic Flora of South Australia
Electronic Flora of South Australia
Census of SA Plants, Algae & Fungi
Identification tools

Electronic Flora of South Australia Family Fact Sheet

FAMILY RHODOMELACEAE Areschoug 1847: 260, nom. cons.

Phylum Rhodophyta

Thallus usually erect and much branched, in some genera foliose and/or prostrate, branches terete, compressed or flat, all erect branches similar or with indeterminate branches bearing determinate laterals of limited growth; adventitious branching in some genera. Holdfast discoid or fibrous, or basal attachment by rhizoids. Structure. Growth monopodial, by transverse or oblique divisions of apical cells, the transverse divisions followed by longitudinal divisions to give pericentral cells and the oblique divisions giving rise to laterals; primary branching exogenous, in some genera later branching endogenous from axial cells or pericentral cells within the cortex, or adventitious. Apices either radial or dorsiventral in symmetry. Pericentral cells 4–24, cut off in alternating order, ecorticate or corticate, in some genera dividing transversely; cortex parenchymatous or rhizoidal, or with rhizoids separating the pericentral or cortical cells; pseudopericentral cells present in some genera. Trichoblasts usually present on subapical cells, in some genera on pericentral or cortical cells, colourless or containing rhodoplasts in some genera. Cells uni- or multinucleate; rhodoplasts usually discoid, often chained in larger cells.

Reproduction: Gametophytes usually dioecious; mixed phases known in some genera. Procarps borne on lower cells of trichoblasts or directly on thallus branches, consisting of a supporting cell (a fertile pericentral cell or its derivative cell) and a (3–) 4-celled carpogonial branch, together with a lateral sterile group; auxiliary cell cut off from the supporting cell after fertilization. Carposporophytes developing from the auxiliary and adjacent cells which usually form a basal fusion cell bearing a usually much-branched gonimoblast with clavate terminal carposporangia replaced from lower cells (i.e. not strictly sympodial branching). Cystocarps ovoid to subspherical, occasionally urceolate; pericarp produced pre-fertilization from cells adjacent to the supporting cell, consisting of erect filaments, each cell with 2–3 outer pericentral cells, ecorticate or corticate, with a narrow to broad ostiole. Spermatangial organs usually borne on branches of trichoblasts or replacing the whole trichoblast, terete or as flat plates and with a monosiphonous stalk, or borne directly on lesser branches of the thallus; the axial cells cut off 2–5 pericentral cells which form a layer of initials which produce an outer layer of spermatangia.

Tetrasporangia produced in polysiphonous, terete, lateral branches or in compressed to flat specialised branches, usually regarded as stichidia, cut off pericentral cells or in some genera from cortical cells, usually with 2–3 presporangial cover cells from the fertile pericentral cell and occasionally a post-sporangial cover cell, with or without a cover of cortical cells. Tetrasporangia tetrahedrally divided, usually subspherical, single per segment and spirally arranged or in a straight row, or twinned and distichously or decussately arranged, or verticillate and 4–6 per segment.

While tribes of the Rhodomelaceae are generally recognised, Kylin (1956) recognised groups and his Lophosiphonia and Placophora groups have not been designated as tribes (with Latin descriptions). There are also several genera doubtfully placed in tribes or unplaced (described below after the tribes/groups), and it may be that recognition of groups is more appropriate for the present state of knowledge of the family. Several species have been placed in Rhodomela or Rytiphloea but are now referred to other genera (see index) of Rhodomelaceae, apart from Rhodomela preissii Sonder 1848: 182 (from W. Aust., holotype in MEL, 45895 - a small inadequate specimen which may be a Hypnea.)


ARESCHOUG, J.E. (1847). Phycearum, quae in maribus Scandinaviae crescunt, enumeratio. Nova Acta R. Soc. Scient. Upsal. 13, 223–382, Plates 1–9.

KYLIN, H. (1956). Die Gattungen der Rhodophyceen. (Gleerups: Lund.)

SONDER, O.W. (1848). Algae. In Lehmann, C., Plantae Preissianae. Vol. 2, pp. 161–195. (Hamburg.)

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

Publication: Womersley, H.B.S. (24 February, 2003)
The Marine Benthic Flora of Southern Australia
Rhodophyta. Part IIID. Ceramiales – Delesseriaceae, Sarcomeniaceae, Rhodomelaceae
Reproduced with permission from The Marine Benthic Flora of Southern Australia Part IIID 2003, by H.B.S. Womersley. Australian Biological Resources Study, Canberra. Copyright Commonwealth of Australia.


1. Thallus terete or compressed, filaments free or laterally fused, segments of pericentral cells usually clear to well below apices, ecorticate or corticated; apical cell filament protruding, not in a depression (occasionally within a flat cleft), subapical cells usually with trichoblasts; pericentral cells usually clear at least near branch apices, forming a clear, well-defined ring in transverse section, sometimes becoming obscured; tetrasporangia cut off only from pericentral cells, single, paired or whorled


1. Thallus parenchymatous, without segments of pericentral cells; apical filament erect in an apical depression, with trichoblasts on subapical cells within the depression or becoming external to it; pericentral cells clear or obscured; tetrasporangia cut off from pericentral or cortical cells but rather obscurely so


2. Thallus usually terete and radially branched; apices radially and not dorsiventrally developed (see Wilsonaea related to the Bostrychieae)


2. Thallus terete to flat, bilaterally or unilaterally branched; apices usually dorsiventrally developed


3. Thallus branches terete, pericentral cells 4–20; trichoblasts non-rhodoplastic, with non-adherent walls at branchings, usually caducous


3. Thallus branches terete or occasionally basally compressed; pericentral cells usually 4, 5 or 7, trichoblasts rhodoplastic, with adherent or non-adherent walls at branchings, caducous or often relatively persistent


4. Branches terete, ecorticate or corticate; pericentral cells 4, 5 or 7 (rarely 6); trichoblasts with Non-adherent walls at branchings; tetrasporangia single and spirally arranged, or opposite per segment


4. Branches terete or compressed, heavily corticated; pericentral cells 4, dividing to form a ring of 7–8, becoming obscure in a rhizoidal medulla; trichoblasts with adherent walls at branchings; tetrasporangia single and spirally arranged in corticated branches bearing trichoblasts


5. Branches terete, discrete (or in some genera congenitally laterally fused); pericentral cells not transversely divided (except some Pterosiphonieae); tetrasporangia usually single (paired in Ophidocladus) per segment


5. Branches terete and discrete, compressed or flat; pericentral cells transversely divided or not; tetrasporangia regularly 2 or more per segment


6. Thallus radially or bilaterally branched, with indeterminate and determinate laterals in defined regular sequences


6. Thallus bilaterally branched but indeterminate and determinate laterals not in defined sequences


7. Indeterminate axes with radial or bilateral determinate laterals; indeterminate apices dorsiventral and usually curved, with 4–16 pericentral cells; trichoblasts present on most determinate laterals


7. Branching bilateral, determinate laterals regularly branched usually adaxially, branches discrete or fused; indeterminate apices dorsiventral, with 6 (or 7) pericentral cells; determinate laterals with no or 3 pericentral cells, arising exogenously usually in 2 ranks; trichoblasts present only on determinate laterals


8. Thallus with prostrate indeterminate, terete, branches bearing erect, terete, determinate laterals endogenously; indeterminate apices curved, dorsiventrally organised; pericentral cells 4–20, ecorticate; tetrasporangia single or paired per segment


8. Thallus with bilateral discrete terete branches or flat with branches congenitally fused; apical arrangement of pericentral cells dorsiventral or not; pericentral cells in some genera (e.g. Pollexfenia) dividing transversely; tetrasporangia single per segment


9. Thallus usually erect, with terete, bilateral determinate branches or flat with polysiphonous branches congenitally fused; 4 or 6 pericentral cells, pericentral cell arrangement at apices not dorsiventral, pericentral cells in some genera dividing transversely


9. Thallus prostrate, flat, with polysiphonous branches congenitally fused; 5 pericentral cells dorsiventrally arranged with 3 dorsally and 2 ventrally, pericentral cells not dividing transversely


10. Branches terete, usually slender with curved apices, dorsiventral or radial; pericentral cells 4–9, dividing transversely to form tiers of 2–5 per axial cell; tetrasporangia in whorls of 4–6


10. Branches compressed to flat or foliose; apices flat or recurved, pericentral cells 4–6, with or without pseudopericentral cells; lateral pericentral cells dividing to form wings 1 or 2 cells thick, ecorticate or corticate; tetrasporangia in opposite pairs


11. Thallus branches flat, linear, apical cell protruding, pericentral cells 4 (5 in fertile segments) with 2 pseudopericentral cells; wings one cell thick, ecorticate; trichoblasts absent; all reproductive cells formed on the thallus surface


11. Thallus branches linear, compressed to foliose; apical cell protruding or within an apical cleft, pericentral cells 5, with or without pseudopericentral cells, or 6; trichoblasts usually present, formed apically or adventitiously on the blade surface; sexual reproductive cells usually originating on reduced or normal trichoblasts


12. Apical cells protruding or in an apical depression; 5 pericentral cells; central axis usually discernible, pericentral cells clear; spermatangia borne on flat, discoid plates with sterile marginal cells, on trichoblasts; tetrasporangia cut off singly from pericentral cells, spirally arranged (rarely 2–3 from a segment)


12. Apical cell always in an apical depression; 2 or 4 pericentral cells; central axis and pericentral cells becoming obscure; spermatangia borne laterally and singly on trichoblasts in the apical depressions or on filaments in subapical pits; tetrasporangia cut off from pericentral cells or from cortical cells


Disclaimer Copyright Disclaimer Copyright Email Contact:
State Herbarium of South Australia
Government of South Australia Government of South Australia Government of South Australia Department for Environment and Water