Schizymenia dubyi (Chauvin ex Duby) J. Agardh
Crustose phase known as Haematocelis rubens J. Agardh
Description: Gametophytes: soft and fleshy, brownish-red fronds, 500 mm long, 250 mm broad, irregularly split or lobed, rarely proliferous, with a very short (2-3 mm) stipe from a minute attachment disc. Tetrasporophyte (Haematocelis-phase): thick fleshy crust; difficult to identify and rarely reported.
Habitat: Gametophytes are found in mid-intertidal, large pools and the shallow subtidal (0-5 m), annual, developing in spring; south-western and western coasts of Britain and Ireland north to St Kilda, uncommon; tetrasporophytic crusts are apparently exclusively found in the shallow subtidal.
Similar species: Dilsea carnosa is much thicker, commoner, and more cartilaginous, has rounded-spathulate blades, and several blades arise from a relatively large basal disk; Halarachnion ligulatum is thin and filmy, never fleshy; Kallymenia reniformis is commoner in the subtidal generally lobed and the lobes are frequently kidney-shaped.
Key characteristics: Fleshy frond, lack of lobing and, generally, marginal proliferations; when dried onto paper the fertile fronds feel like fine sandpaper to the the touch.