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Electronic Flora of South Australia Genus Fact Sheet
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 envelopment of host axes 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 apparently occurring mainly within actively dividing subepithallial initials that are usually as long as or longer 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 apparently arise from groups of subepithallial initials; gametangia and carposporangia formed on separate thalli from tetrasporangia and bisporangia.
Gametangial thalli monoecious or dioecious; carpogonia and spermatangia produced in separate conceptacles. Carpogonia terminating 2–4-celled filaments arising from the female conceptacle chamber floor. Mature carposporophytes apparently lacking a conspicuous central fusion cell and composed either of an irregularly shaped fusion cell that may appear discontinuous in section or of a several-celled fusion cell complex (not always evident) and of short gonimoblast filaments bearing terminal carposporangia. Spermatangial filaments unbranched, borne on the floor, walls and roof of male conceptacle chambers.
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.
Lectotype species: M. lichenoides (Ellis) Lemoine 1928:251; designated by Ishijima (1942, p. 174). Basionym: Corallium lichenoides Ellis 1768:407, pl. 17 figs 9–11.
Taxonomic notes: Mesophyllum, as delimited here, incorporates the conclusions of Woelkerling & Harvey (1992, pp. 395–397) who have updated the generic concept presented in Woelkerling (1988, p. 191). Over 140 species and infraspecific taxa have been ascribed to Mesophyllum (Woelkerling 1988, p. 195); most are poorly known. Woelkerling & Irvine (1986b) give a detailed account of the type species; further information on and references to additional accounts of M. lichenoides are included in Woelkerling & Harvey (1993, p. 596). Details relating to generic etymology, nomenclature, synonymy, etc. are provided by Woelkerling (1988, pp. 191–196). This account of southern Australian species follows Woelkerling & Harvey (1992; 1993).
Notes on other taxa reported from southern Australia
Woelkerling & Harvey (1993, pp. 596–600) provide information on nine additional species that at some stage were ascribed to Mesophyllum and reported from southern Australia. These include species whose status is uncertain, incorrect records, heterotypic synonyms of other species of Mesophyllum and species now known to belong to other genera or conspecific with taxa belonging to other genera.
References:
ELLIS, J. (1768). Extract of a letter from John Ellis Esquire, F.R.S. to Dr. Linneaus of Upsal, F.R.S. on the animal nature of the genus of zoophytes, called Corallina. Phil. Trans. R. Soc. Lond. 57(1), 404–427, Plates 17, 18.
ISHIJIMA, W. (1942). The first find of Mesophyllum from the Tertiary of Japan. J. Geol. Soc. Jap. 49, 174–176. Note: Concurrently published with Transactions and Proceedings of the Palaeontological Society of Japan 149 :153–155; both sets of page numbers appear in the paper.
LEMOINE, M.(Mme P.) (1928). Un nouveau genre de Mélobésiées: Mesophyllum. Bull. Soc. bot. Fr. 75, 251–254. Effective publication date: between 23.iii.1928 and 27.iv.1928 (dates of two successive 'meetings' of the society).
WOELKERLING, W.J. & HARVEY, A. (1992). Mesophyllum incisum (Corallinaceae, Rhodophyta) in southern Australia: implications for generic and specific delimitation in the Melobesioideae. Br. phycol. J. 27, 381–399.
WOELKERLING, W.J. & HARVEY, A. (1993). An account of sourthern Australian species of Mesophyllum (Corallinaceae, Rhodophyta). Aust. Syst. Bot. 6, 571–637.
WOELKERLING, W.J. & IRVINE, L.M. (1986b). The neotypification and status of Mesophyllum (Corallinaceae, Rhodophyta). Phycologia 25, 379–396.
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.
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 MESOPHYLLUM
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1. Tetrasporangial and bisporangial conceptacle roofs mound-like or flattened (Figs 83A, 85A), not differentiated into a peripheral rim and a central, sunken pore-plate | 2 |
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1. Tetrasporangial and bisporangial conceptacle roofs volcano-like, differentiated into a peripheral rim and a central somewhat sunken pore-plate (Figs 87A, 88D) | 3 |
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2. Tetrasporangial and bisporangial conceptacle pore canals bordered by cells that are similar in size and shape to other roof cells above the chamber (Fig. 82D) | M. engelhartii |
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2. Tetrasporangial and bisporangial conceptacle pore canals bordered by cells (especially near the base of the canal) that are narrower and more elongate than adjacent roof cells (Fig. 84F) | M. incisum |
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3. Tetrasporangial conceptacle pore canals bordered by cells that are similar in size and shape to other roof cells above the chamber (Fig. 86D) | M. macroblastum |
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3. Tetrasporangial conceptacle pore canals bordered by cells (especially near the base of the canal) that are narrower and more elongate than adjacent roof cells (Fig. 89B, C) | M. printzianum |
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