- Name also: Thymeleaf Sandwort
- Family: Pink Family – Caryophyllaceae
- Growing form: Annual herb.
- Height: 5–20 cm (2–8 in.). Stem ascending–erect, usually abundantly branched, short-haired.
- Flower: Corolla regular (actinomorphic), white, under 1 cm (0.4 in.) broad; petals 5, entire, shorter than sepals. Sepals 5, tapered, 3-veined, short-haired. Stamens 10. Gynoecium syncarpous, with 3 styles. Flowers in a sparse corymb (sometimes solitary).
- Leaves: Opposite, lowest unclearly stalked, upper almost stalkless. Blade triangularly ovate, under 1 cm (0.4 in.), tapered, with entire margins, finely haired, greyish green.
- Fruit: Pear-shaped, oval-based, thick-walled, light brown, 6-valved, capsule same length as calyx.
- Habitat: Rocky and hillside ridges, meadows, gravel patches, sandy banks, river banks, road and railway embankments, fallow fields, wasteland, yards.
- Flowering time: June–August.
Thyme-leaved sandwort is quite a small plant which can evade even the sharp-eyed botanist’s gaze. Usually the species is only as tall as a finger, and with its small leaves it looks quite skinny. The best places to look for it are dry, sandy hillside ridges and thin-soiled rocky outcrops, whose open vegetative cover has space for the short-lived thyme-leaved sandwort. Its small size is a benefit on a meadow: it needs less water and nutrients and it develops quicker than larger species. Thyme-leaved sandwort won’t grow in any old patch of bare ground, however, because it demands relatively nutritious soil. Human activity has opened up new areas for it to grow, in fallow fields, sandy roadsides and gardens, where it often grows bigger than it does in the wild. It has also spread with people from its native European habitat to North America and Australia.
The petals on thyme-leaved sandwort’s flowers are shorter than its sepals. It usually flowers at the beginning of summer, but continues to some extent throughout its growing season. Thyme-leaved sandwort’s flowers can be used to differentiate it from the other members of its genus that grow in Finland, Arctic sandwort (A. norvegica) and fringed sandwort (A. pseudofrigida). Thyme-leaved sandwort is more common in the southern half of Finland – although casual finds can be made until the southern border of Lapland, it doesn’t really share any common habitat with Arctic sandwort, which grows on the high fell tundra of the north-west “arm” of Finland, or fringed sandwort, which thrives on the calciferous rocks of Koillismaa.