- Name also: Seaside Plantain, Goose Tongue (USA)
- Family: Plantain Family – Plantaginaceae
- Growing form: Perennial herb.
- Height: 10–30 cm (4–12 in.). Stem leafless, with arching base, round, sparsely haired scape.
- Flower: Corolla regular (actinomorphic), reddish, small, approx. 3 mm wide, fused, 4-lobed; lobes membraneous. Calyx 4-lobed. Stamens 4, filaments long, anthers pale yellow. Pistil fused, a single carpel. Carpels mature before stamens (protogynous). Inflorescence a long, cylindrical (occasionally short–globose) spike.
- Leaves: In basal rosette, unclearly stalked. Blade linear–linearly elliptic, fleshy, with entire margins (sometimes sparsely toothed), almost glabrous, parallel-veined, greyish green, often with black spot.
- Fruit: Capsule, opening like a lid.
- Habitat: Sea shores, sea-side meadows, beside salted roads.
- Flowering time: June–August.
Sea plantain is well-equipped to stand up to the rage of the sea in its habitats: its strong taproot pushes down deep into the ground to anchor it, the narrow, fleshy, slightly wax-covered and strong leaves grouped into a tight rosette can stand spray from the sea and its flexible scapes bend in furious storms without breaking. Sea plantain was among the first vascular plants to get a foot-fold in cracks in the outermost rocks in the archipelago. The species thrives in calm coastal meadows too, if the waves and ice have made room for it to grow beside other plants. On grazing land it grows an often small but profuse flowering scape. In Finland there are no suitable habitats inland so salt-loving plants are limited to growing in coastal areas The species might grow slightly further away from the water line if the wind carries the spray of the surf far enough inland. It has also been able to grow beside roads which are heavily salted during the winter. Its relative shoreweed (Littorella uniflora) grows on damper places along the shore line and is recognisable by its small, narrow, stiff-leaved basal rosette.
Many plantains have extended their habitat with the help of people, especially perhaps greater plantain (P. major), which is common all across the northern hemisphere. Sea plantain has demonstrated its ability to reach new growing places under its own steam because it is also known to grow on the southern tip of South America, in Tierra del Fuego, Patagonia and the Falkland Islands approximately 9,000 kilometres from its closest North American stand. These are not different subspecies. Presumably the plant has travelled with migrating birds, perhaps only after the end of the Ice Age.