The marine diatom genus rhizosolenia: A new approach to the taxonomy

The silica wall in 35 species of the marine planktonic diatom genus Rhizosolenia Brightwell has been examined with light and electron microscopy. The genus Rhizosolenia is revised and an emended circumscription comprising 24 species is proposed. Five new species (Rh. acicularis, Rh. borealis, Rh. ostenfeldii, Rh. fallax, Rh. decipiens) and four new infraspecific taxa (Rh. polydactyla f.squamosa, Rh. castracanei var. neglecta, Rh. antennata f. semispina, Rh. sima f. silicea) are described. Rh. calcar-avis Schultze has been transferred to the new genus Pseudosolenia, and Rh. alata Brightw. to the new genus Proboscia. Several traditional Rhizosolenia species are regarded as belonging to other genera but pending further research are retained in the genus.

The taxonomy of the species recognized in Rhizosolenia, Pseudosolenia and Proboscia, and the circumscription of the family Rhizosoleniaceae are discussed. The use of the concepts of species, variety and form in diatom taxonomy is discussed. A key is provided. All taxa are illustrated.