The blades are monostromatic, that is composed of a layers of single cells, and can grow to 25 cm long.

[1][2] Other similar algae include: Apoglossum ruscifolium, Hypoglossum hypoglossoides and Membranoptera alata all of which are much smaller.

[2] Phycodrys rubens is of comparable size but can be easily distinguished having lobed edges to the blades.

[1] Growing on rock in pools at low water and also sublittoral to 30 m deep epiphytic on other large algae.

[1][2] Common around Ireland, Great Britain, Isle of Man, Channel Islands, to the north to Norway and Iceland south in Spain.