- Written also: Wall-lettuce
- Latin synonym: Lactuca muralis
- Family: Daisy Family – Compositae, subfamily Cichorioideae (formerly Chicory Family – Cichoriaceae)
- Growing form: Perennial herb.
- Height: 30–80 cm (12–30 in.). Stem usually unbranched, glabrous, often reddish violet.
- Flower: Single flower-like capitula 10–15 mm (0.4–0.6 in.) broad, surrounded by involucral bracts. Capitulum flowers (usually 5) yellow, tongue-like, tip 5-toothed. Stamens 5. Gynoecium composed of 2 fused carpels. Involucre round, slender, involucral bracts in 2 rows, broadly triangular–almost linear, outer bracts much shorter than inner. Capitula borne in a lax corymbose cluster.
- Leaves: Alternate, part long-stemmed, stalk winged, stipule-like at base. Blade pinnate, shallow-toothed, glabrous, thin, underside bluish green, terminal leaflet triangular, lower lobes small.
- Fruit: Narrowly elliptic, strongly veined, almost black, 3–4 mm (0.12–0.16 in.) long cypsela, crowned with unbranched hairs on a short stalk.
- Habitat: Shady spruce woods and rich mixed swamps, broad-leaved forests on the lower parts of mountains and rocky places, stream valleys, springs, clear-fell areas, beside walls and ruins, parks, gardens, pavements, roadsides.
- Flowering time: July–August.
Wall lettuce’s habitat in the south of Finland represents its northernmost limit. It likes the sea and a temperate climate, and grows in Finland in more-or-less the same areas that hardwood trees thrive. It is most commonly found along the coast on the Åland Islands, south-west Finland and the province of Uusimaa. It becomes quickly rarer towards the north, although there are still remote individual stands in Central Finland.
Wall lettuce is native in Finland to broad-leaved forests, rich mixed swamps and shady corners by rock walls. Unlike many other demanding broad-leaved forest plants, wall lettuce has become more common in recent years and established itself in new growing places. Its appearance in new broad-leaved forests is a consequence of the end of forest grazing. Although wall lettuce doesn’t really belong to lettuce’s genus, hares in the forest as well as domestic pets are very partial to it. Cattle used to be grazed in particularly lush parts of the forest, where they would eat wall lettuce shoots, but broad-leaved forests are now returning to their natural state and wall lettuce is reclaiming its territory in the wild. Stronger herds of elk and deer cause big local variances in its numbers, but roaming herds of wild animals are unable to decimate it completely in any given area.
Wall lettuce makes use of the way that forestry disturbs the environment with logging and excavation work, and it has spread through its abundant seed production from the shade of the forest to join people in forest parks, yards and gardens. In cultural places it has made itself particularly at home around old ruins and forts. The damp shade and calciferous substrate created by crumbling plaster at the bottom of battle graves, furnaces and pits allows it to grow an abundance of shoots and angular leaves, as well as its candy-floss-like inflorescence.