Electronic Flora of South Australia Genus Fact Sheet

Genus PHYMATOLITHON Foslie 1898a: 4, nom. cons.

Phylum Rhodophyta – Class Florideophyceae – Order Corallinales – Family Corallinaceae – Subfamily Melobesioideae

Thallus encrusting to warty, lumpy, fruticose, discoid, layered or foliose, epigenous and partially to completely affixed by cell adhesion, or unattached and free-living as rhodoliths; genicula absent. Structure pseudoparenchymatous; organisation dorsiventral in crustose portions but radial in protuberant branches; construction monomerous, consisting of a single system of branched, laterally cohering, filaments that collectively contribute to a ventrally or centrally situated core and a peripheral region where portions of core filaments or their derivatives curve outwards towards the thallus surface; cell elongation occurring mainly behind actively dividing subepithallial initials that are usually as short as or shorter than their immediate inward derivatives; cells of adjacent filaments joined by cell-fusions; secondary pit-connections absent; epithallial cells terminating most filaments at thallus surface, distal walls rounded or flattened but not flared; trichocytes occasional in some species; haustoria unknown.

Reproduction: Vegetative reproduction by thallus fragmentation. Gametangia and carposporangia borne in uniporate conceptacles; tetrasporangia and bisporangia borne in multiporate conceptacles that arise adventitiously from groups of vegetative cells within the thallus; gametangia and carposporangia formed on separate thalli from tetrasporangia and bisporangia.

Gametangial thalli monoecious or dioecious; carpogonia and spermatangia usually produced in separate conceptacles. Carpogonia terminating 2- or 3-celled filaments arising from the female conceptacle chamber floor. Mature carposporophytes apparently lacking a conspicuous central fusion cell and composed of short gonimoblast filaments bearing terminal carposporangia. Both unbranched and branched spermatangial filaments present, borne on the male conceptacle chamber floor, walls and roof.

Tetrasporangia and bisporangia scattered across the conceptacle chamber floor, roofs formed by filaments interspersed amongst and peripheral to sporangial initials; each mature sporangium containing zonately arranged tetraspores or bispores and possessing an apical plug that blocks a roof pore prior to spore release.

Type species: P. polymorphum (Linneaus) Foslie 1898a: 4. Basionym: Millepora polymorpha Linnaeus 1767: 1285. M. polymorphum Linnaeus is a superfluous substitute name for M. calcarea Pallas (1766, p. 265), and thus, as noted by Woelkerling & Irvine (1986a), the correct name of the type species of Phymatolithon is P. calcareum (Pallas) Adey & McKibbin (1970, p. 100).

Taxonomic notes: Phymatolithon, as delimited here, incorporates the conclusions of Wilks & Woelkerling (1994) who found that characters proposed by Chamberlain (1990) and by Chamberlain & Keats (1994) to delimit Leptophytum from Phymatolithon were unsatisfactory and that Leptophytum is a genus in need of further evaluation. At least 40 species and infraspecific taxa have been ascribed to Phymatolithon; most are poorly known. Woelkerling & Irvine (1986a) gave a detailed account of tetrasporangial thalli of the type species, but noted that gametangia and carposporophytes are not known with certainty and have yet to be studied in a modern context. Moreover, early stages of carposporophyte development and gonimoblast filament ontogeny are poorly known in most species ascribed to the genus. Thus, information on gametangia and carposporophytes provided in the generic description is incomplete and will require revision once new data on the type and other species become available. Details relating to generic etymology, nomenclature, synonymy, etc. are provided by Woelkerling (1988, pp. 197–203). The proposal (Irvine & Woelkerling 1986) to conserve Phymatolithon Foslie (1898a) against Apora Gunnerus (1768) was approved by the Fifteenth International Botanical Congress in Tokyo in August 1993. This account of southern Australian species follows Wilks & Woelkerling (1994).

References:

ADEY, W.H. & MCKIBBIN, D. (1970). Studies on the maerl species Phymatolithon calcareum (Pallas) nov. comb. and Lithothamnion coralloides Crouan in the Ria de Vigo. Botanica Mar. 13, 100–106.

CHAMBERLAIN, Y.M. (1990). The genus Leptophytum (Rhodophyta, Corallinaceae) in the British Isles with descriptions of Leptophytum borneti, L. elatum sp. nov. and L. laeve. Br. phycol. J. 25, 179–199.

FOSLIE, M. (1898a). Systematical survey of the lithothamnia. K. norske Vidensk. Selsk. Skr. 1898(2), 1–7.

GUNNERUS, J.E. (1768). On nogle Norske Coraller. K. norske Vidensk. Selsk. Skr. 4, 38–73, Plates 1–4, 8, 10, 11, 15.

IRVINE, L.M. & WOELKERLING, W.J. (1986). Proposal to conserve Phymatolithon against Apora (Rhodophyta : Corallinaceae). Taxon 35, 731–733.

LINNAEUS, C. (1767). Systema naturae. 12 edn. Vol. 1 (Salvii: Stockholm.)

PALLAS, P.S. (1766). Elenchus Zoophytorum. (P. van Cleef: Hague.)

WILKS, K.M. & WOELKERLING, W.J. (1994). An account of southern Australian species of Phymatolithon (Corallinaceae, Rhodophyta) with comments on Leptophytum. Aust. Syst. Bot. 7, 183–223.

WOELKERLING, W.J. & IRVINE, L.M. (1986a). The neotypification and status of Phymatolithon (Corallinaceae, Rhodophyta). Br. phycol. J. 21, 55–80.

WOELKERLING, Wm.J. (1988). The Coralline Red Algae. [British Museum (N.H.): London.]

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

Author: W.J. Woelkerling

Publication: Womersley, H.B.S. (28 June, 1996)
The Marine Benthic Flora of Southern Australia
Rhodophyta. Part IIIB. Gracilarialse, Rhodymeniales, Corallinales and Bonnemaisoniales
Reproduced with permission from The Marine Benthic Flora of Southern Australia Part IIIB 1996, by H.B.S. Womersley. Australian Biological Resources Study, Canberra. Copyright Commonwealth of Australia.

KEY TO SPECIES OF PHYMATOLITHON

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