- Name also: Fanleaf Geranium
- Family: Geranium Family – Geraniaceae
- Growing form: Annual herb.
- Height: 15–50 cm (6–20 in.). Stem usually upper part branching, blunt-edged, densely hairy, upper part clearly sticky.
- Flower: Regular (actinomorphic), 15–20 mm (0.6–0.8 in.) wide. Petals 5, purple, dark-veined, with notched tips. Sepals 5, dark-veined, hairy, bristle-tipped, spreading, almost same length as petals, growing significantly in fruiting stage. Stamens 10, filaments hairy. Gynoecium composed of 5 fused carpels. Flowers axillary in pairs or terminating stem.
- Leaves: In basal rosette and opposite on stem or sometimes solitary. Basal leaves long-stalked, usually withering in flowering stage, stem leaves long-stalked–short-stalked, stipulate. Blade roundish–5-cornered, commonly wider than long, with palmate venation, deeply (3–)5–7-lobed; lobes wide, large-toothed.
- Fruit: 5-parted schizocarp, tip beak-like, curling in a roll as it ripens. Mericarps glossy, hairy.
- Habitat: Burned places, controlled burning areas, base of campfire sites, logging clearings, forest roadsides, waste ground, gardens.
- Flowering time: June–September.
- Endangerment: Near threatened.
Hardy geranium is the only Finnish vascular plant that has adapted to burned fields, and in fact its seeds require heat treatment before they will sprout. Usually only a forest fire will wake the seeds up from their dormant state, but sometimes also fierce sunshine on bare forest land is enough to do the job. The species probably adapted to take advantage of the open and nutritious environment that fire leaves in its wake.
Hardy geranium’s way of life is quite insecure, especially nowadays when fire prevention is a priority: it grows somewhat randomly, usually alone where there has been a bonfire, in road-work sites and in logging clearings. It can appear abundantly if there is a forest fire or on the site of a Midsummer bonfire, although the stand will be short-lived. Most genus Geranium plants’ beak-like infructescences open with a sudden explosion, sending the seeds flying out over a couple of metres. Hardy geranium’s schizocarps are green until the last phase of maturation before turning black overnight when the beak eventually dries. The mature tip begins to twist into a roll along its length. In this way it improves its chances of sticking to the clothes, fur or feathers of nearby creatures in the burned area so that the mericarps can hopefully end up in a new suitable area. Before it withers the annual species can autogamously produce hundreds of seeds which can remain dormant in the soil for decades before sprouting at the next opportunity.