- Name also: Common Skullcap, Marsh Skullcap, Hooded Skullcap
- Family: Mint Family – Lamiaceae (Labiatae)
- Growing form: Perennial herb. Rootstock thin, slightly creeping.
- Height: 10–50 cm (4–20 in.). Stem unbranched or branching until base, 4-edged, hairy along edges.
- Flower: Corolla irregular (zygomorphic), blue (occasionally white), with purple tip, 10–20 mm (0.4–0.8 in.) long, fused, bilabiate, long-tubed. Corolla upper lip convex, calyx-tube curved gently upwards. Calyx campanulate (bell-shaped), bilabiate, back with clear protruberance, glabrous–fine-haired, closed while in fruit. Stamens 4, of which 2 long and 2 short. Gynoecium composed of 2 fused carpels. Flowers in pairs, a sparse group terminating stem.
- Leaves: Opposite, short-stalked. Blade narrowly ovate, with tapered tip, with shallowly cordate or blunt base, sparsely blunt-toothed. Flowers’ subtending bracts like stem leaves, longer than lowest flowers at least.
- Fruit: 4-sectioned schizocarp. Mericarps yellowish brown, granular.
- Habitat: Shores of waterside meadows that are prone to flooding, coastal hedgerows, damp meadows, rich swamps, springs, ditch and stream banks.
- Flowering time: July–August.
Skullcap thrives in many kinds of damp habitats. It is common, if not necessarily very abundant or conspicuous, in damp and low-lying land almost across the whole country. It has spread to the banks of little streams along the upper course of rivers as well as to the shores of islands on the outer archipelago due to its efficient vegetative propagation and abundant seed production. The species spreads vegetatively via its thin subterraneous runners and often forms sparse little groups. Skullcap also spreads successfully sexually. The flower’s throat is almost closed because the middle part of the lower lip presses tightly against the upper lip. Pollinators – mainly hymenopterans and butterflies – still find their way however to the middle part of the flower from the side. After flowering the calyx lips close tightly against each other. After the carpels have ripened the upper lid of the calyx separates like a lid and the carpels remain in the shelf that is created by the lower lip. As people, animals or the wind move the rigid, withered stem the seeds can fly quite a long way.
Altogether there are 200–300 skullcap species (Scutellaria spp.), depending where you draw the line. Another skullcap species, spear-leaved skullcap (S. hastifolia), can be found along the coastline in south-west and southern Finland. It can be recognized by its hastate-based leaves, larger flowers, and denser, often one-sided inflorescence.