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Exilicrusta Y.M.Chamberlain, 1992

Classification:
Empire Eukaryota
Kingdom Plantae
Subkingdom Biliphyta
Phylum Rhodophyta
Subphylum Eurhodophytina
Class Florideophyceae
Subclass Corallinophycidae
Order Hapalidiales
Family Hapalidiaceae
Subfamily Melobesioideae

Holotype species: Exilicrusta parva Y.M.Chamberlain

Original publication and holotype designation: Chamberlain, Y.M. (1992). Observations on two melobesioid crustose coralline red algal species from the British Isles - Exilicrusta parva, a new genus and species, and Lithothamnion sonderi Hauck. British Phycological Journal 27: 185-201.

Precise date of publication1 June 1992 (stated at top of first page of original publication). The requirements for valid publication are specified in the ICBN (International Code of Botanical Nomenclature).

Taxonomic status: currently recognized as a distinct genus.

Most recent taxonomic treatment adopted: Schneider, C.W. & Wynne, M.J. (2007). A synoptic review of the classification of red algal genera a half a century after Kylin's "Die Gattungen der Rhodophyceen". Botanica Marina 50: 197-249.

Nomenclatural notes
The ICBN rules cited below are those adopted by the Seventeenth International Botanical Congress, Vienna, Austria, July 2005 (McNeill et al. 2006).

In accordance with ICBN Art. 13.3, the name Exilicrusta is treated as pertaining to a non-fossil taxon because its type is based on a non-fossil specimen. No species based on fossil types have been assigned to the genus to date.

The generic name Exilicrusta is typified (ICBN Art 10.1) by the type of E. parva, the only species originally included in the genus. - (28 Aug 2009) -

Description: Plants calcified, lacking genicula, entirely pseudoparenchymatous; encrusting in growth-form; epigenous and growing completely attached to rock (the only known substrate); 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) 1 or more cells long that arise perpendicularly from cells of ventral filaments and lead to increase in thallus thickness. Upright filaments each normally terminating at the thallus surface in an epithallial cell; outermost epithallial cell walls flattened with flared corners; cell elongation tending to occur mainly in subepithallial initials that are usually as long as or longer than their inward derivatives. Cells of adjacent filaments linked by fusions; secondary pit-connections unknown. Gametangia and carposporangia developing in uniporate conceptacles. Spermatangia (male gametangia) and carpogonia (female gametangia) produced in separate conceptacles that usually form adjacent to one another on the same plant. Spermatangia terminal on unbranched filaments that arise from the conceptacle chamber floor but not the roof; spermatangial initials not observed; mode of spermatangial conceptacle roof formation uncertain. Carpogonia terminating 3-celled unbranched filaments arising from the conceptacle chamber floor. Carposporophytes developing in carpogonial conceptacles after presumed fertilization, each composed of a central fusion cell and several-celled filaments that arise peripherally and bear terminal carposporangia. Tetrasporangia formed in conceptacles on separate plants from gametangia and carposporangia. Roofs of tetrasporangial 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 unknown.

Information contributed by: Wm. J. Woelkerling. The most recent alteration to this page was made on 20 Jan 2017 by M.D. Guiry.

Characters considered diagnostic of Exilicrusta: The lists below of diagnostic characters of Exilicrusta, and of the higher taxa to which it belongs, are derived from data in Chamberlain (1992), Chamberlain & Irvine (1994), 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 Exilicrusta from other genera of the Hapalidiaceae, subfamily Melobesioideae). Harvey, Woelkerling & Millar (2003: 653) also provide a diagnostic comparison of Exilicrusta with other currently recognized non-fossil genera of Melobesioideae, and Chamberlain (1992: 199, 200, Table 1) includes further comparisons of Exilicrusta, Lithothamnion, and Melobesia.

Characters considered diagnostic of higher taxonomic ranks known/presumed to occur in all species of Exilicrusta: Exilicrusta is the only known genus of Hapalidiaceae, Subfamily Melobesioideae with: 1) dimerous thallus construction throughout; and 2) epithallial cells flattened and possessing flared corners. Characters considered diagnostic of higher taxonomic ranks and known/presumed to occur in the only known species of Exilicrusta: 1) calcification in the form of calcite; 2) pit plugs with two cap layers at cytoplasmic faces, the outer cap dome shaped; membrane absent; 3) cell walls impregnated with calcite; 4) gametangia and carposporangia produced within uniporate conceptacles; 5) tetrasporangia/bisporangia produced within conceptacles and possessing zonately arranged spores; 6) tetrasporangial/bisporangial conceptacles possessing multiporate plates or roofs; 7) tetrasporangia/bisporangia producing apical plugs; 8) tetrasporangial/bisporangial conceptacles with multiporate roofs composed of cells; lacking an acellular multiporate plate recessed below a single outer opening; and 9) cells of contiguous vegetative filaments linked exclusively by cell fusions. Characters 1-2 are considered diagnostic of the Corallinophycidae, 3-5 of the Corallinales, 6-7 of the Hapalidiaceae, and 8-9 of the Melobesioideae.

Generic synonyms: No synonyms of Exilicrusta are known.

Comments: Knowledge of Exilicrusta and the single known species, E. parva, is based on the original detailed account of the type and other collections by Chamberlain (1992) and the subsequent floristic treatment in Chamberlain & Irvine (1994: 162-165), who describe the species as small, obscure, difficult to find, and known from only a few specimens. In terms of growth-form (Woelkerling et al. 1993), plants of Exilicrusta are classed as encrusting. The extent to which the gametangial characters mentioned by Chamberlain (1992: 200, Table 1) are diagnostic of Exilicrusta requires further study because of the apparent rarity of Exilicrusta, and because for many species of Lithothamnion and Melobesia, spermatangia, carpogonial branches, and/or carposporophytes are unknown or poorly known. These characters have not been included in the list below.

Biogeographically, Exilicrusta presently is known only from several collections gathered on the south coast of England.

Numbers of names and species: There is only one species or infraspecific name in the database at present, which has been flagged as accepted taxonomically on the basis of the listed literature under the species name. In some instances, opinions on taxonomic validity differ from author to author and users are encouraged to form their own opinion. AlgaeBase is a work in progress and should not be regarded as a definitive source only as a guide to the literature..

Names: ('C' indicates a name that is accepted taxonomically; 'S' a homotypic or heterotypic synonym; 'U' indicates a name of uncertain taxonomic status, but which has been subjected to some verification nomenclaturally; 'P' indicates a preliminary AlgaeBase entry that has not been subjected to any kind of verification. For more information on a species click on it to activate a link to the Species database):

Click here to also show infraspecific names in the list below.

References
Chamberlain, Y.M. (1992). Observations on two melobesioid crustose coralline red algal species from the British Isles - Exilicrusta parva, a new genus and species, and Lithothamnion sonderi Hauck. British Phycological Journal 27: 185-201.

Chamberlain, Y.M. & Irvine, L.M. (1994). Melobesioideae Bizzozero. In: Seaweeds of the British Isles. Volume 1. Rhodophyta Part 2B Corallinales, Hildenbrandiales. (Irvine, L.M. & Chamberlain, Y.M. Eds), pp. 159-234. London: HMSO.

Harvey, A.S., Broadwater, S.T., Woelkerling, W.J. & Mitrovski, P.J. (2003). Choreonema (Corallinales, Rhodophyta): 18S rDNA phylogeny and resurrection of the Hapalidiaceae for the subfamilies Choreonematoideae, Austrolithoideae and Melobesioideae. Journal of Phycology 39: 988-998.

Harvey, A.S., Woelkerling, W. J. & Millar, A.J.K. (2003). An account of the Hapalidiaceae (Corallinales, Rhodophyta) in south-eastern Australia. Australian Systematic Botany 16: 647-698.

Harvey, A.S., Woelkerling, W.J. & Millar, A.J.K. (2009). The genus Amphiroa (Lithophylloideae, Corallinaceae, Rhodophyta) from the temperate coasts of the Australian continent, including the newly described A. klochkovana. Phycologia 48: 258-290.

Le Gall, L. & Saunders, G.W. (2007). A nuclear phylogeny of the Florideophyceae (Rhodophyta) inferred from combined EF2, small subunit and large subunit ribosomal DNA: establishing the new red algal subclass Corallinophycidae. Molecular Phylogenetics and Evolution 43: 1118-1130.

Le Gall, L., Payri, C.E., Bittner, C.E., & Saunders, G.W. (2010). Multigene polygenetic analyses support recognition of the Sporolithales, ord. nov. Molecular Phylogenetics and Evolution 54(1): 302-305.

McNeill, J., Barrie, F.R., Burdet, H.M., Demouline, V., Hawksworth, D.L., Marhold, K., Nicolson, D.H., Prado, J., Silva, P.C., Skog, J.E., Wiersema, J.H. & Turland, N.J. (2006). International Code of Botanical Nomenclature (Vienna Code) adopted by the Seventeenth International Botancial Congress Vienna, Austria, July 2005. pp. [i-iv], v-xviii + 1-568. Liechtenstein: A.R.G. Gantner Verlag.

Woelkerling, W.J., Irvine, L.M. & Harvey, A.S. (1993). Growth-forms in non-geniculate coralline red algae (Corallinales, Rhodophyta). Australian Systematic Botany 6: 277-293.

Woelkerling, W.J., Millar, A.J.K., Harvey, A. & Baba, M. (2008). Recognition of Pachyarthron and Bossiella as distinct genera in the Corallinaceae, subfamily Corallinoideae (Corallinales, Rhodophyta). Phycologia 47: 265-293.

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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.

Created: 28 December 2000 by M.D. Guiry

Verified by: 20 January 2017 by M.D. Guiry

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M.D. Guiry in Guiry, M.D. & Guiry, G.M. 2018. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. http://www.algaebase.org; searched on 18 September 2018.

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