Acrosiphonia J.Agardh, 1846

Type species: a type species (generitype) appears not to have been designated.

Original publication: Agardh, J.G. (1846). Anadema, ett nytt slägte bland Algerna. Kongl. Vetenskaps-Adademiens F├Ârhandlingar, Stockholm 3: 103-104.

Description: Plants soft and spreading when young, later stiff, compact and ropelike, 2(-3) to 10(-15) cm high, composed of uniseriate, branched upright filaments, 50(-60) to 250 um in diameter. Plants attached by multicellular, branched, downgrowing rhizoids from the lower end of basal cells, occasionally by pseudoparenchymatous holdfast. Filaments generally increasing in diameter towards apices. Percurrent axes inconspicuous or absent. Branching intercalary, usually alternate or opposite, sometimes secund, appressed, with blunt or acuminate tips, straight or variously incurved, hooked or entangled. Plants morphologically variable depending on age and environment. Mature cells multinucleate. Chloroplast parietal, largely perforate in elongated cells, much denser in older cells, containing many polypyramidal pyrenoids with matrix penetrated by chloroplast stroma tubules. Plasmodesmata present in cross walls. Diplohaplontic heteromorphic and haplontic life histories present, with sexual reproduction in haploid bisexual or unisexual filamentous plants. Gametogenesis by synchronous divisions of nuclei, and cleavage of cytoplasm, without participation of large central vacuole. Gametes liberated through semicircular aperture with crenated margin and a retained (usually) operculum. Gametangia solitary to many in long rows, formed by intercalary branch cells. Induction of gametogenesis correlated with cessation of growth and long days. Gametes ejected from gametangium in a sac that bursts, releasing motile gametes. Gametes biflagellate, pear-shaped or posteriorly acuminate, with pyrenoid and double layered stigma. Zygotes usually develop into unicellular, uninucleate, stalked Codiolum-phase; on maturity forming quadriflagellate, ovoid zoospores with meiosis in first nuclear division. Zoospores produce new filamentous gametophytes. In haplontic life cycle, meiosis also during first nuclear division. Hypnozygote germinates directly into new haploid gametophyte. In both life cycles "false" binucleate zygotes formed following suppression of karyogamy and apokaryogamic strains occur. Unfused gametes can develop directly into new gametophytes especially in asexual strains. Parthenogenetic production of Codiolum-like plants reported. Plants easily multiplied by fragmentation. Chromosome numbers of n=4 and 5. Acrosiphonia widespread in cold temperate to arctic marine waters of both hemispheres, occasionally in brackish water. Species epilithic or epiphytic in eulittoral and occasionally in sublittoral zones. In the Atlantic, Acrosiphonia now reduced to 3-4 species; elsewhere in need of revision. Growth mainly by division and elongation of apical cells. A cytoplasmic band forms about 1/4 to 1/5 of cell length back from tip and all nuclei above the band migrate into it, forming a ring up to six nuclei high and four nuclei thick. Synchronous mitosis of nuclei in band and proximity occurs. After mitosis the original band containing daughter nuclei is displaced apically, and slightly basally, and cytokinesis occurs approximately at base of original band. Apical cell receives most daughter nuclei and continue elongating, but elongation of subapical cell insignificant. In intercalary cells nuclei also form a band, occupying an equatorial position with only one layer of nuclei. After synchronous mitosis nuclei partitioned equally into daughter cells which do not elongate but continue to deposit cell wall. In rapidly growing plants apical cells divide about 1 h after entering dark cycle. During mitosis the nuclear envelope remains mostly intact, except for gaps at each pole permitting spindle microtubules to extend to paired centrioles. No distinct kinetochores observed. Centrioles (absent in interphase nuclei) may be located approximately at right angles; interzonal spindle present. Cytokinesis characterized by ingrowth of cleavage furrow preceded by a group of microtubules. Cell wall multilayered with randomly oriented fibrils, ultrastructurally with herringbone, microfibrillar structure and thin surface membrane; polysaccharides of sulfated glucuronozylorhamnans. Ultrastructure of flagellar apparatus includes two overlapping basal bodies in a 11/5 o'clock (counterclockwise) position, cruciately arranged microtubules (2-X-2-X, where X=3) and terminal cap. Other details include a non-striated capping plate covering two proximal sheaths, a tiny second proximal connecting fibre, striated bands linking three-membered rootlets to proximal sheaths, and electron dense material partially covering two-membered rootlets. Mating structures present in upper part of gamete. After gamete fusion, four roughly cruciately arranged basal bodies and eight sets of rootlets present. Two basal bodies, each from opposite mating types, almost touching by proximal ends, whereas others considerably displaced. Four sets of rootlets (2-3-2-3) associated in fusion plane. In opposite plane rootlets always separated.

Information contributed by: S. J├│nsson. The most recent alteration to this page was made on 2021-10-20 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: Gabrielson, P.W., Lindstrom, S.C. & O'Kelly, C.J. (2012). Keys to the seaweeds and seagrasses of Southeast Alaska, British Columbia, Washington, and Oregon. Phycological Contribution No. 8. pp. [i]-iv, 1-192. Hillsborough, North Carolina: PhycoID.

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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. 20 October 2021. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway.; searched on 04 December 2022

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