| Summary: | The diversity of red algae is significantly increasing; in the recent interest of climate changes, taxonomic and biogeographic studies are needed in untouched regions such as ecological important islands. We examined a collection of <i>Gelidium</i> specimens gathered during the 2010 Atimo Vatae expedition based on the morphology and DNA sequencing of mitochondrial <i>cox</i>1 and plastid <i>rbc</i>L. Both morphological and molecular datasets demonstrated the presence of three species in Madagascar; <i>G. leptum</i> G.H.Boo, L.Le Gall and H.S.Yoon, sp. nov., described here, and <i>G. sclerophyllum</i> W.R.Taylor and <i>G. usmanghanii</i> Afaq-Husain and Shameel. <i>Gelidium leptum</i> is distinguished by thin, slender, flattened thalli with irregular branches, compactly arranged thick-walled cells in medulla, sparse rhizoidal filaments at both sides of branches, and elongate sori of tetrasporangia. <i>Gelidium sclerophyllum</i>, previously considered as endemic to the Tropical Eastern Pacific, is first reported in the Indian Ocean and Hawai’i; <i>G. usmanghanii</i>, previously reported to occur in Pakistan and Oman, also presents a first record in the Southern Hemisphere. Phylogenies inferred from <i>cox</i>1 and <i>rbc</i>L sequences suggests that each of the three species likely diverged from different ancestors. The Madagascan <i>Gelidium</i> comprises two geographical elements; Madagascan endemic (<i>G. leptum</i>) and widespread species (<i>G. sclerophyllum</i> and <i>G. usmanghanii</i>).
|
|---|