Mesophyllum Me.Lemoine, 1928

Lectotype species: Mesophyllum lichenoides (J.Ellis) Me.Lemoine

Original publication: Lemoine, M. (1928). Un nouveau genre de Mélobésiées: Mesophyllum. Bulletin de la Société Botanique de France 75: 251-254.

Type designated in: Ishijima, W. (1942). The first find of Mesophyllum from the Tertiary of Japan. Journal of the Geological Society of Japan 49: 174-176.

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Precise date of publication:

between 23 March and 27 April 1928 (see Woelkerling & Lamy 1998: 721 for details) The requirements for valid publication are specified in the ICBN (International Code of Botanical Nomenclature).

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. algae, sponges, 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) reportedly present in most species to varying degrees. 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 within actively dividing subepithallial initials that are usually as long as or longer 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 formed on the same or on different plants. Spermatangia (where known) formed on unbranched filaments that arise from the conceptacle chamber floor and roof; spermatangial initials (where known) at first each overlain by a ‘protective cell’ that soon degenerates; 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 2-4 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 large conspicuous central fusion cell but composed of an irregularly shaped fusion cell or a several-celled fusion-cell-complex (not always evident) and 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 2024-05-13 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 neuter.

Most recent taxonomic treatment adopted: Athanasiadis, A. & Ballantine, D.L. (2024). Anatomy and classification of the Mesophyllaceae (Corallinales, Rhodophyta), based on phylogenetic principles. Smithsonian Contributions to Botany 118: [i]-xii, [1]-216, 83 figures, 6 tables.

Comments: Information on the taxonomic history, nomenclature, and other matters associated with the name Mesophyllum is contained in Woelkerling (1988: 193-195). Growth form terminology (encrusting, lumpy, fruticose, etc.) follows Woelkerling et al. (1993).

An account of the epitype specimen of M. lichenoides (J. Ellis) M. Lemoine, the lectotype species of Mesophyllum, is presented in Woelkerling & Irvine (1986); additional data on isoepitype material (LTB 16595) are provided in Woelkerling & Harvey (1993: 596 & figs 30A-30B).

The types and other specimens of most species currently referred to Mesophyllum need to be re-examined in detail to verify whether generic placement is correct, to re-assess whether recognition as a distinct species 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. At present, most species assigned to Mesophyllum are poorly or incompletely known.

Biogeographically, Mesophyllum appears to be widespread, but many records require confirmation.

The lists below of diagnostic characters of Mesophyllum, 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 Le 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 Mesophyllum 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:
M.D. Guiry in Guiry, M.D. & Guiry, G.M. 13 May 2024. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. https://www.algaebase.org; searched on 21 November 2024