Range expansion of some non-indigenous seaweeds along the coasts of Brittany - English Channel Author Burel, Thomas Author Helias, Mathieu Author Duff, Michel Le text Botanica Marina 2023 Warsaw, Poland 2023-05-01 66 3 151 164 http://dx.doi.org/10.1515/bot-2023-0002 journal article 10.1515/bot-2023-0002 1437-4323 11360276 3.2 Botryocladia wrightii (Harvey) W.E. Schmidt, D.L. Ballantine et Fredericq 2017 Botryocladia wrightii is a Rhodymeniaceae originating from the North-West Pacific, initially described from Japan by Harvey in 1860 as Halosaccion wrightii . It was first found outside its native distribution area in 1978 in the Thau Lagoon as Chrysymenia wrightii Harvey ( Ben Maiz 1986 ) . Botryocladia wrightii was found in 2005 in the North-East Atlantic ( Galicia , North-West Spain ) under the name Chrysymenia wrightii ( Bárbara et al. 2008 ) . It was discovered in the Gulf of Morbihan in 2010 ( Le Roux 2018 ) and reached the coasts of England in 2013 ( Bunker 2014 ). All specimens found in this study were collected in the lower part of the intertidal zone with a deposit of sand. This species develops a tubular hollow thallus, somewhat gelatinous, more or less cylindrical, with a color from golden orange to purplish ( Figure 5a ). The largest sampled specimens were up to 20 cm , with main axes up to 0.6 cm wide ( Figure 5b ). The thallus is attached to the substratum by a discoid holdfast and shows numerous branches with an irregular branching pattern. In transverse section, the center of the thallus appears hollow with a cortex consisting of small cortical cells and large subcortical cells ( Figure 5c ). Cystocarpic plants were found in Tréveneuc ( Figure 5d ). When present, cystocarps (up to 1000 µm) are numerous and protrude all over the thallus. Specimens of B . wrightii can be confused with the native Dumontia contorta (S. G. Gmelin) Ruprecht , but differ in the branching pattern, the inner structure of the thallus and the arrangement of cystocarps.