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A new monotypic family for the enigmatic crustose red alga Plagiospora gracilis.

Maggs, C. and Saunders, G.W., 2016. A new monotypic family for the enigmatic crustose red alga Plagiospora gracilis. Botanical Journal of the Linnean Society, 182 (1), 1-13.

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DOI: 10.1111/boj.12450


Plagiospora gracilis, a mucilaginous crustose red alga growing on subtidal pebbles on both coasts of the North Atlantic Ocean, forms distinctive tetrasporangia (red algal meiotic structures that release haploid tetraspores) but gametophytes have never been reported. In the absence of gametangia, the taxonomic position of this monotypic genus has always been uncertain; it is currently placed provisionally in the Gloiosiphoniaceae (Gigartinales) by comparison with sporophytes of Gloiosiphonia obtained in culture. Dioecious gametophytic crusts of P. gracilis are now reported for the first time, forming gametangia in inconspicuous superficial sori. There is no evidence that fertilization ever occurs in the field although fertile males and female were collected together. In culture, tetraspores grew into tetrasporophytes for three successive generations, by presumed apomictic sporophyte recycling. The life history of P. gracilis may represent a late stage in the loss of sexual reproduction leading to tetraspore-to-tetrasporophyte life histories such as that in Hildenbrandia. Phylogenetic analysis of sequences of the rbcL, LSU (28S) rDNA and coxI (COI-5P) genes for P. gracilis with other Gigartinales resolved P. gracilis as a distinct lineage in a well-supported clade of the families Sphaerococcaceae, Gloiosiphoniaceae, Endocladiaceae, Nizymeniaceae and Phacelocarpaceae. We here propose the monotypic Plagiosporaceae fam. nov. to accommodate P. gracilis.

Item Type:Article
Additional Information:Funded by NSERC
Uncontrolled Keywords:apomixis; evolution; Gigartinales; life-history; molecular systematics; phylogeny;Rhodophyta Botanical
Group:Faculty of Science & Technology
ID Code:23752
Deposited By: Symplectic RT2
Deposited On:26 May 2016 15:22
Last Modified:14 Mar 2022 13:56


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