Porphyra C.Agardh, 1824: xxxii, 190

Classification:
Empire Eukaryota
Kingdom Plantae
Subkingdom Biliphyta
Phylum Rhodophycophyta
Subphylum Eurhodophytina
Class Bangiophyceae
Subclass Bangiophycidae
Order Bangiales
Family Bangiaceae

Holotype species: Porphyra purpurea (Roth) C.Agardh

Original publication: Agardh, C.A. (1824). Systema algarum. pp. [i]-xxxviii, [1]-312. Lundae [Lund]: Literis Berlingianis.
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Type designated in Silva, P.C. (1952). A review of nomenclatural conservation in the algae from the point of view of the type method. University of California Publications in Botany 25: 241-323.

Taxonomic status: currently recognized as a distinct genus.

Description: Thallus a foliose blade, one or two cells in thickness and ranging in size from a few mm to over 3 m in length. Blades arise singly from a small discoid holdfast. Stipe absent or minute. Basal cells have rhizoids. Blades ranging in morphology from orbicular to linear, with margins smooth, dentate, or ruffled depending on the species. One or two stellate chloroplasts with large central pyrenoid per cell. Contains R-Type II phycoerythrin. Pit plugs absent in the foliose phase. In early stages of development growth is apical followed by a shift to diffuse growth. The microscopic, filamentous conchocelis phase consists of short, uniseriate, branched filaments that penetrate calcareous substrata such as oyster shell and barnacles. Cells of the conchocelis have parietal, band-shaped chloroplasts. Pit plugs present. The foliose phase of many, but not all species may reproduce asexually by archeospores, agamospores, or neutral spores. Archeosporangia are formed when the entire contents of a vegetative cell differentiate and are released as a single, wall-less archeospore that undergoes bipolar germination to give rise to a new blade. This type of archeospore production is typical of young stages of many foliose thalli. In a few species even larger thalli produce abundant, marginal archeosporangia. In a few species, vegetative cells form neutral sporangia that undergo repeated periclinal and anticlinal division to form "packets" of neutral spores. These neutral spores are released by wall gelatinization and undergo bipolar germination to form new blades. Agamosporangia form in the same way as neutral sporangia and the agamospores are also asexual, however, they undergo unipolar germination to form haploid conchocelis. Such agamospore production is often, but not always, a facultative, asexual derivative of an otherwise sexual life history. Sexual reproduction is present in many, but not all species. The foliose phase is either a monoecious, dioecious, or androdioecious gametophyte. Spermatangia formed when vegetative cells undergo a series of anticlinal and periclinal divisions to form packets of spermatia. Spermatia are white to yellowish in appearance due to disintegration of the chloroplast during spermatogenesis. Mature spermatia contain a highly condensed nucleus and numerous fibrillar vesicles containing mucopolysaccharides. The carpogonium can be a morphologically undifferentiated cell or a cell that has uni or bipolar trichogynes. Following fertilization the carpogonium becomes the zygotosporangium and undergoes a series of periclinal and anticlinal divisions to form "packets" of diploid zygotospores that are released by dissolution of the surrounding cell wall. Zygotospores germinate into a microscopic, filamentous conchocelis phase. Under certain temperature and daylength regimes the conchocelis phase forms thick, conchosporangial branches that release conchosporangia. Site of meiosis would appear to be variable depending on strain differences or environmental factors. In some species meiosis has been reported to occur in the conchosporangium at the time of conchospore formation. Somatic meiosis has also been documented, occuring in the released conchospore. The haploid nuclei produced are not incorporated into four spores and dispersed, therefore the foliose thallus, resulting from conchospore germination, is a genetic chimera.

Comments: The biology of this genus has been extensively investigated because of its economic value to the mariculture industry in the production of Nori. Foliose thalli epiphytic or saxicolous, growing from the high intertidal zone to the shallow subtidal. Foliose thalli are short-lived annuals, some being summer species and some winter species. In contrast, the conchocelis phase is probably perennial. Cosmopolitan, widely distributed in temperate waters, polar and tropical seas. Center of diversity in the North Pacific. A recent molecular study of relationships within the genus has cautioned that it may contain a polyphyletic assemblage of taxa that have all converged on a simple blade morphology. The presumed antiquity of Porphyra is further confirmed by a recent molecular study that found it to have the most primitive plastid genome known.

NCBI Nucleotide Sequences

Numbers of names and species: There are 264 species (and infraspecific) names in the database at present, of which 117 have been flagged as currently accepted taxonomically.

Names: ('C' indicates a name that is currently 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):

Information contributed by: M. Hawkes. The most recent alteration to this page was made on 8 Apr 2007 by M.D. Guiry.

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.