Orthoseira Thwaites, 1848

Holotype species: Melosira americana Kützing

Currently accepted name for the type species: Orthoseira americana (Kützing) Round, R.M.Crawford & D.G.Mann ex Spaulding & Kociolek

Original publication and holotype designation: Thwaites, G.H.K. (1848). Further observations on the Diatomaceae with descriptions of new genera and species. Annals and Magazine of Natural History, Series 2 1: 161-172, pls XI, XII.

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Description: Cells cylindrical, united to form short filaments with valve faces closely appressed. Interlocking spines can be seen between cells and a characteristic thickening of the girdle bands can be seen in mid-focus. The plastids are numerous, small and discoid. They are peripheral while the nucleus is suspended centrally on cytoplasmic bridges through the vacuole. A small genus of sub-aerial diatoms commonly found among bryophytes especially in alkaline areas. Valve views of the acid-cleaned valves show 2-5 characteristic tube processes at the centre of the face. Rows of areolae radiate from near the centre and pass over the valve rim and down the mantle. At the rim in most species there are well-defined spines. These are simple and triangular in side view or pyramidal with stellate bases and are found between rows of areolae. In O. densrophila the ring of spines is interrupted by clusters of distinctive areolae. In intact sibling valves these clusters of pores are precisely aligned with each other. The valve is a simple laminate layer of silica. While the areolae are covered on the inner surface by a velum or some other form of siliceous layer the pores in the clusters are left unoccluded. Though it is improbable that the marginal spines serve to link neighbouring cells, they would prevent torsion or rotation of siblings vis-à-vis one another. Cells are probably bound together by mucilage secretions passed through the tube process. These are unique fluted passages through the valve with simple internal openings and well-defined collars to the outside, described as 'carinoportulae' by Crawford (1979a). The cingulum is composed of a number of bands whose pars interior is greatly thickened. In O. dendroteres the bands are so angled as to give the effect of a spiral arrangement. The bands are sufficiently robust to leave a step on the mantle of one of the sibling valves similar to that observed in Ellerbeckia.

The most recent alteration to this page was made on 2024-08-28 by G.M. Guiry.

Taxonomic status: The taxonomic status of this entity requires further investigation.

Gender: This genus name is currently treated as feminine.

Most recent taxonomic treatment adopted: Danz, A., Van de Vijver, B., Kochman-Kedziora, N., Kusber, W.-H., Guerrero, J., Vouillous, A., Salam S.E., Liu, Q. & Kociolek, J.P. (2022). The genus Orthoseira Thwaites: historical overview, current status and recommendations for the future. Nova Hedwigia 115(1-2): 1-29, 16 figs, 1 table.

Comments: Auxospores are covered by a layer of scales similar to those reported from Melosira (Crawford, 1974a).

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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.

Linking to this page: https://www.algaebase.org/search/genus/detail/?genus_id=45923

Citing AlgaeBase
Cite this record as:
G.M. Guiry in Guiry, M.D. & Guiry, G.M. 28 August 2024. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. https://www.algaebase.org; searched on 22 November 2024