- Name also: Rueleaf Saxifrage
- Family: Saxifrage Family – Saxifragaceae
- Growing form: Annual herb.
- Height: 4–15 cm (1.6–6 in.). Stem branched at base, abundantly leaved, usually with glandular hairs.
- Flower: Corolla regular (actinomorphic), white, approx. 0.7 cm (0.28 in.) wide; petals five, 3–4 mm (0.12–0.16 in.) long, 2 times as long as sepals, round-tipped. Sepals 5, erect. Stamens 10. Styles 2, fused at base. Flowers solitary in axils.
- Leaves: In basal rosette and alternate along stem, basal leaves withering early, stalked, upper leaves stalkless. Rosette leaf blades obovate, stem leaf blades elliptic–lanceolate, 3–5-lobed or with entire margins.
- Fruit: 2-parted, spherical capsule.
- Habitat: Dry rocky slopes, grassy rocky outcrops, walls, dry stone walls, bird rocks. Calciphile.
- Flowering time: May–June.
- Endangerment: Near threatened.
Most genus Saxifrage plants are perennials in cold, mountainous areas, so as an annual that grows in low-lying areas, rue-leaved saxifrage is an exception. It has been developing its own direction for a long time, and it has many special features which are a consequence of the extremely quick development of an individual plant. The species is probably native to the Mediterranean climate, which has produced equally quickly developing and quickly withering annuals.
Rue-leaved saxifrage grows in the south-west of Finland. Its typical habitat is bird rocks, but the species is not needlessly demanding as long as the soil is alkaline and nitrogenous and sunny, with not too much shade from neighbours. It often grows on rocks that have a thin layer of soil and cracks in rocks alongside other small annuals. Rue-leaved saxifrage flowers early in the spring, ripens its seeds quickly and completely withers. It is completely dependent on its seed production and for that reason, for safety’s sake, it is probably mainly self-pollinating. The seeds sprout at the end of the same summer and form a basal rosette by the autumn, so the species is an autumn annual.
Rue-leaved saxifrage is one of the smallest and most delicate of the saxifrages that grow in Finland, and it is sometimes only a few centimetres tall. Despite its small size it is often easy to spot: it has clearly reddish or even completely scarlet. Good identification markers are also its leaves, which are shallowly lobed at the tips and which have given it the scientific name tridactylis, ‘three-fingered’. As the flowering stem develops in the spring the rosette dies off, and as the flowers open, only the withered remains of the leaves are left.