- Name also: Greater Spearwort, Water Spearwort
- Family: Buttercup Family – Ranunculaceae
- Growing form: Perennial herb. Rootstock long, creeping. With runners.
- Height: 50–120 cm (20–50 in.). Stem erect, hollow, sparsely branched, above water short-haired.
- Flower: Corolla regular (actinomorphic), yellow, 25–45 mm (1–1.8 in.) wide; petals 5, longer than sepals. Sepals 5, long-lasting. Receptacle glabrous. Stamens many. Gynoecium separate, with many pistils. Flowers 1–8 terminating branches, flower-stalk glossy, densely hairy.
- Leaves: Alternate, basal leaves long-stalked, withering early, stem leaves short-stalked–stalkless. Basal leaf blades long ovate–elliptic–lanceolate, slightly hairy, often with weakly toothed margin. Stem leaf blades lanceolate, hairy on both sides parallel to surface, narrow-based, sparsely serrated margins–with entire margins. Plants in deep water with narrow floating leaves.
- Fruit: Elliptic, flat, winged on one side, 2–2,5 mm (0.08–0.1 in.) long achene, tip with 0.5–1 mm (0.02–0.04 in.) long bristle. Achenes in clusters..
- Habitat: Shallow stream and river banks and lake shores, estuaries, sometimes in flood-influenced swamps.
- Flowering time: July–August.
Great spearwort is the largest and most handsome of Finland’s Ranunculus plants. (The large size of great spearwort’s flower shows up well when it is compared to meadow buttercup.) It raises its flower over one metre above the surface of the water. Despite its impressive flower great spearwort does not produce so much seed – rather it propagates itself quite efficiently through axillary bulbils and runners up to half a metre long.
Great spearwort thrives on river banks and rapids. It also does well in shallow bays and flooding open bogs, but it is clearly a more modest plant when it is in standing water. It is sensitive to turbid and silty water, which explains why it doesn’t grow in clay-rich river beds in southern Finland. Great spearwort’s wide but fragmented habitat reaches all the way north to Sodankylä inside the Arctic Circle. This is probably a legacy from the warm climate that followed the last Ice Age: the temperature was much warmer then than it is now, and many southern species could be found further north. As the climate has become cooler and wetter, great spearwort has moved south, but it has survived in some favourable places as a reminder of that time. Wild flora changes slowly, and its rhythms are influenced by people in many ways.