Phymatolithon Foslie, 1898, nom. cons.

Holotype species: Phymatolithon polymorphum Foslie

Currently accepted name for the type species: Phymatolithon calcareum (Pallas) W.H.Adey & D.L.McKibbin ex Woelkering & L.M.Irvine

Original publication and holotype designation: Foslie, M. (1898). Systematical survey of the Lithothamnia. Det Kongelige Norske Videnskabers Selskabs Skrifter 1898(2): 1-7.

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Precise date of publication: 14 October 1898 (see Woelkerling 1993: 278 for details).

Description: Plants calcified, lacking genicula, entirely pseudoparenchymatous; encrusting to warty, lumpy, fruticose, discoid, layered or foliose; epigenous and growing partially to completely attached to the surface of various substrates (e.g. molluscs, rock), or growing unattached and free-living as rhodoliths; haustoria unknown.

Thallus organization generally dorsiventral in crustose portions but more or less radial in branches; thallus construction monomerous throughout, consisting of a single system of branched laterally coherent filaments that contribute to a ventral or central core and a peripheral region where portions of core filaments or their derivatives curve outwards towards the thallus surface; coaxial growth (in which cells of adjacent filaments in core region are aligned in arching tiers) apparently not. Most filaments usually terminating at the thallus surface in epithallial cells (generally one per filament); outermost walls of epithallial cells rounded or flattened but not flared at the corners; 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 linked by fusions; secondary pit-connections unknown.

Gametangia (where known) and carposporangia (where known) developing in uniporate conceptacles. Spermatangia (male gametangia) and carpogonia (female gametangia) produced in separate conceptacles; male and female conceptacles occasionally formed on the same plant but much more commonly formed on different plants. Spermatangia (where known) formed on branched and unbranched filaments that arise from the conceptacle chamber floor and roof; spermatangial initials (where known) apparently not overlain with protective cells during early stages of development; spermatangial conceptacle roof formation (where known) occurring centripetally from groups of vegetative filaments peripheral to developing spermatangial filaments on the conceptacle chamber floor. Carpogoina (where known) terminating 2-3 celled unbranched filaments that arise from the conceptacle chamber floor. Carposporophytes (where known) developing in carpogonial conceptacles after presumed fertilization; mature carposporophytes apparently lacking a conspicuous central fusion cell but possessing several-celled filaments bearing terminal carposporangia.

Tetrasporangia/bisporangia formed in conceptacles on separate plants from gametangia and carposporangia. Roofs of tetrasporangial/bisporangial conceptacles multiporate and composed of cells. Tetrasporangia each containing four zonately arranged spores and producing an apical plug that blocks a roof pore before spore release. Bisporangia each containing two spores but otherwise similar to tetrasporangia.

Information contributed by: Wm. J. Woelkerling. The most recent alteration to this page was made on 2021-08-10 by E.A. Molinari Novoa.

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

Gender: This genus name is currently treated as neuter.

Most recent taxonomic treatment adopted: Irvine, L.M. & Woelkerling, W.J. (1986). Proposal to conserve Phymatolithon against Apora (Rhodophyta: Corallinaceae). Taxon 35: 731-733.

Comments: Comments: Information on the taxonomic history, nomenclature, and other matters associated with the name Phymatolithon is contained in Woelkerling (1988: 197-203). Growth form terminology (encrusting, lumpy, fruticose, etc.) follows Woelkerling et al. (1993).

An account of the epitype specimen of Phymatolithon calcareum, the type species of Phymatolithon, is presented in Woelkerling & Irvine (1986). Cabioch (1970) provides information on gametangial plants, and additional data on the species, including references is summarized in Chamberlain & Irvine (1994: 212-215).

The types and other specimens of a number of species and infraspecific taxa currently referred to Phymatolithon need to be re-examined in detail to verify whether generic placement is correct, to re-assess whether recognition as a distinct species or infraspecific taxon is justified, to understand more fully the extent of infraspecific morphological and anatomical variation, and to determine the diagnostic characters that separate each species from others within the genus and each infraspecific taxon from others assigned to the same species. At present, a number species and infraspecific taxa assigned to Phymatolithon are poorly or incompletely known.

Biogeographically, Phymatolithon is recorded fromtemperate and colder water environments in both the northern and southern hemispheres, but a number of published records require confirmation.

The lists below of diagnostic characters of Phymatolithon, and of the higher taxa to which it belongs, are derived from data in Harvey, Broadwater, Woelkerling & Mitrovski (2003), Harvey, Woelkerling & Millar (2003), Le Gall & Saunders (2007), Woelkerling et al. (2008: 282) and/or Lre Gall et al. (2009) Diagnostic characters are those that taken together distinguish a taxon from others of the same taxonomic rank (e.g. characters distinguishing Phymatolithon from other genera of the Hapalidiaceae, subfamily Melobesioideae). Harvey, Woelkerling & Millar (2003: 653) also provide a diagnostic comparison of Mesophyllum with other currently recognized non-fossil genera of Melobesioideae.

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Contributors
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:
E.A. Molinari Novoa in Guiry, M.D. & Guiry, G.M. 10 August 2021. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. https://www.algaebase.org; searched on 11 August 2022

 
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