- Name also: Tiny Mousetail
- Family: Buttercup Family – Ranunculaceae
- Growing form: Annual herb.
- Height: 3–12 cm (1.2–4.8 in.). Stem delicate.
- Flower: Perianth regular (actinomorphic), pale yellow, 5–8 mm (0.2–0.32 in.) wide. Petals 5–7, yellowish white or reddish, linear, tubular, often lacking. Sepals 5, lanceolate, spurred. In fruiting stage receptacle extends up to 5 cm (2 in.) long. Stamens 5 or more. Gynoecium separate, with many pistils. Flowers solitary, terminating scape.
- Leaves: A basal rosette, long-stalked, glabrous. Blade barely wider than stalk, linear, with entire margins, blunt, glabrous.
- Fruit: Flat, brown, often slightly hairy, 1–1.5 mm (0.04–0.06 in.) long achene. Achenes with elongated (5–7 cm) receptacle pressed against one another.
- Habitat: Dry meadows, archipelago bird rocks, rocky yards, roadside embankments, paths, car tracks, fallow land, fields, gardens, flower beds in parks.
- Flowering time: May–June.
Mousetail is an overwintering annual. In early spring it grows quickly in the damp ground left by melting snow and ice. The plant sometimes begins to open its inconspicuous flower in May when it is only a few centimetres high. The small flower’s almost tubular petals are visited by flies, but mousetail often has to pollinate itself. As the seeds ripen the gynoecium and receptacle extend, becoming tens of times larger than before, and at this stage there is no doubt about where the plant got its name: its similarity to a mouse’s scaly tail is obvious. The plant has a marvellous seed production and can reproduce quickly in a favourable environment.
Delicate and low-growing mousetail cannot compete with larger competitors. The species favours rich, open habitats and likes a lot of nitrogen and quite neutral soil. In a large part of Finland it only grows in culturally influenced places, as a weed in fields and yards. Southern Finnish seashores where the rocks have been fertilized by bird and fish excrement, and calcium has been added from mussel shells, could have been mousetail’s original habitat. Mousetail is however highly adaptable and even grows in holes that have been left by crumbling plaster.