Rhodymenia Greville, 1830, nom. cons.

Holotype species: Rhodymenia palmetta (Stackhouse) Greville

Currently accepted name for the type species: Rhodymenia pseudopalmata (J.V.Lamouroux) P.C.Silva

Original publication and holotype designation: Greville, R.K. (1830). Algae britannicae, or descriptions of the marine and other inarticulated plants of the British islands, belonging to the order Algae; with plates illustrative of the genera. pp. [i]-lxxxviii, [1]-218, pl. 1-19. Edinburgh & London: McLachlan & Stewart; Baldwin & Cradock.

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Description: Thallus with erect or prostrate, usually stipitate fronds, arising from a basal disc or stolons, blades flattened, cartilaginous, simple or divided dichotomously, palmately or irregularly, sometimes with marginal or apical proliferations, occasionally perforate. Construction multiaxial, cortex of 2-5 layers of small pigmented axially elongated cells. Medulla compact, pseudoparencymatous, with large axially elongated almost colourless cells. Gametangial plants dioecious. Spermatangia in small subapical sori or large irregular patches scattered over blade, produced superficially from outer cortical cells. Procarpic, carpogonial branches 3- or 4-celled borne on a large multinucleate supporting cell also bearing a 2-celled auxiliary cell branch, gonimoblast developing outwards often with 2-3 lobes, almost all cells forming carposporangia. Cystocarps hemispherical, large and protruding, ostiolate, formed apically or scattered, tela arachnoidea absent. Tetrasporangia in subapical sori, scattered throughout the blade, or formed in special proliferations, formed in an intercalary position in unmodified cortex. Spores regularly cruciately arranged.

Information contributed by: M.D. Guiry. The most recent alteration to this page was made on 2024-06-16 by M.D. Guiry.

Taxonomic status: This name is of an entity that is currently accepted taxonomically.

Gender: This genus name is currently treated as feminine.

Comments: Culture studies of Rhodymenia pseudopalmata and R. holmesii Ardissone from Ireland and R. natalensis Kylin from South Africa (Guiry unpubl. obs.) were inconclusive. Although the plants grew rapidly at 20°C, no reproduction was observed under a range of temperature and daylength conditions. It is likely, however, that all species of Rhodymenia have a 'Polysiphonia-type' life history. Guiry (1977) described what may be vegetative reproductive structures occurring on the fronds of R. delicatula P.J.L. Dangeard from the British Isles. Chromosome numbers of n = 28 and 2n = 30-40 have been reported in R. pertusa from Japan (Yabu 1976) and n = 10 and 2n = 20 in R. pseudopalmata (Cole 1990).

Several morphological forms are apparent within the genus: species growing from discs vs stolons; erect vs prostrate species; species in which the tetrasporangia are localised in apical sori vs scattered throughout the thallus; species in which growth is monopodial vs ramisympodial (the latter were previously included in Dendrymenia). A range of sizes is also apparent within the genus: some species become reproductively mature at 15-20 mm (e.g., Rhodymenia delicatula), some at 50-100 (e.g., R. pseudopalmata, R. pacifica), and some at 120-1000 mm (e.g., R. pertusa).

Epymenia, regarded by some as a genus of about 14 species restricted to the colder seas of the Southern Hemisphere (South Africa, Tristan da Cunha, the Falkland I., Chile, Australasia and Kerguelen I.; see Sparling 1957: 348), and occurring mainly in the subtidal at depths of 2-60 m. Formerly separated from Rhodymenia on the basis of forming reproductive structures in specially formed leaflets, the genus is now considered synonymous with Rhodymenia (Womersley, 1996; Saunders et al., 1999).

Rhodymenia is thus a world-wide genus of some 54 species, mainly occurring in warmer waters from the lower intertidal to depths of about 100 m. In his revision of the genus, Dawson (1941) recognized many species on what appeared at first sight to be somewhat tenuous grounds; with experience, however, it becomes clear that many of the entities recognized by Dawson are indeed good species, but are difficult to distinguish without extensive material.

The spelling Rhodymenia, used by Montagne (1839), has been conserved against the original spelling Rhodomenia, used by Greville (1830). The name is to be cited as Rhodymenia Greville (1830).

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Some of the descriptions included in AlgaeBase were originally from the unpublished Encyclopedia of Algal Genera, organised in the 1990s by Dr Bruce Parker on behalf of the Phycological Society of America (PSA) and intended to be published in CD format. These AlgaeBase descriptions are now being continually updated, and each current contributor is identified above. The PSA and AlgaeBase warmly acknowledge the generosity of all past and present contributors and particularly the work of Dr Parker.

Descriptions of chrysophyte genera were subsequently published in J. Kristiansen & H.R. Preisig (eds.). 2001. Encyclopedia of Chrysophyte Genera. Bibliotheca Phycologica 110: 1-260.

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Citing AlgaeBase
Cite this record as:
M.D. Guiry in Guiry, M.D. & Guiry, G.M. 16 June 2024. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. https://www.algaebase.org; searched on 19 July 2024

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