Melobesia J.V.Lamouroux, 1812

Holotype species: Melobesia membranacea (Esper) J.V.Lamouroux

Original publication and holotype designation: Lamouroux, [J.V.F.] (1812). Extrait d'un mémoire sur la classification des Polypiers coralligènes non entièrement pierreux. Nouveaux Bulletin des Sciences, par la Société Philomathique de Paris 3: 181-188.

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Precise date of publication: 1812 (more precise date not determined). The requirements for valid publication are specified in the ICBN (International Code of Botanical Nomenclature).

Description: Plants calcified, lacking genicula, largely or entirely pseudoparenchymatous; encrusting; and epigenous and normally growing completely attached to the surface of various substrates (most commonly other algae); haustoria unknown.

Thallus organization wholly dorsiventral; thallus construction dimerous throughout, composed of two groups of filaments: a ventral-most unistratose layer of filaments (primigenous filaments) from which marginal growth occurs; and upright filaments (postigenous filaments) one or more cells long that arise perpendicularly from cells of ventral filaments and lead to increased thallus thickness. Upright filaments each normally terminating at the thallus surface in an epithallial cell; outermost epithallial cell walls rounded or flattened but not flared at the corners; subepithallial cell elongation characteristics uncertain. 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 different conceptacles; male and female conceptacles occasionally formed on the same plant but much more commonly formed on different plants. Spermatangia (where known) formed on unbranched filaments arising from the conceptacle chamber floor and roof; layer of degenerative ‘protective cells’ overlying spermatangial initials not recorded; mode of spermatangial roof formation uncertain. Carpogonia (where known) terminating 2-3 celled unbranched filaments arising from the conceptacle chamber floor. Carposporophytes (where known) developing in carpogonial conceptacles after presumed fertilization, apparently composed either of one (or possibly several) inconspicuous fusion cells or lacking an evident fusion cell, but always 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 2023-05-18 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.

Most recent taxonomic treatment adopted: Athanasiadis, A. (2016). Phycologia Europaea Rhodophyta Vol. I. pp. [i]-xxxxviii, 1-762. Thessaloniki: Published and distributed by the author.

Comments: Information on the taxonomic history, nomenclature, and other matters associated with the name Melobesia Lamourouxis contained in Woelkerling (1988: 189-190), and additional data are provided in Wilks & Woelkerling (1991). Growth form terminology follows Woelkerling et al. (1993).

Accounts of the epitype specimen of Melobesia membranacea, the type species of Melobesia Lamouroux, are presented in Chamberlain (1985) and Wilks & Woelkerling (1991)..

Uncertainty attends the mode of spermatangial conceptacle roof formation in Melobesia. Based on drawings and comments in Kylin (1928:39-40, Fig 20, as Epilithon), repeated by Suneson (1937: 60-61, as Epilithon), Lebednik (1978:392) and Chamberlain et al.(1995: 450-451) suggested that roof formation in Melobesia was similar to that in Clathromorphum (in which the roof forms vertically from filaments that also produce vertical pairs of spermatangial initials that at first are linked by primary pit-connections (Lebednik 1978: 394, fig. 12); the conceptacle chamber forms vertically when the pairs of spermatangial initials split apart). Kylin’s (1928) observations have yet to be confirmed, and apparently there are no published photographic figures showing early developmental stages for any species currently placed in Melobesia.

The types and other specimens of most species currently referred to Melobesia Lamouroux 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 Melobesia are poorly or incompletely known

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

The lists below of diagnostic characters of Melobesia, 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 Melobesia from other genera of the Hapalidiaceae, subfamily Melobesioideae). Harvey, Woelkerling & Millar (2003: 653) also provide a diagnostic comparison of Melobesia with other currently recognized non-fossil genera of Melobesioideae.

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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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M.D. Guiry in Guiry, M.D. & Guiry, G.M. 18 May 2023. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway.; searched on 18 April 2024

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