Zostera marina var. angustifolia, Zostera marina
General description:
Zostera angustifolia was (and sometimes still is) used for narrow-leaved, intertidal ecotypes. Some British authors still treat them as a separate species, though this is not supported by phylogeny (Coyer et al, 2013), nor population genetics (Talbot et al, 2016; Olsen et al, 2013). Nonetheless, this ecotype is ecologically and morphologically distinctive, so we retain it as a variety to prevent loss of information.