- Name also: Smooth Rupture-wort
- Family: Pink Family – Caryophyllaceae
- Growing form: Annual or short-lived perennial herb.
- Height: 1–3 cm (0.2–1.2 in.). Stem procumbent, 5–15 cm (2–6 in.) long, many-branched, sparsely short-haired.
- Flower: Corolla regular (actinomorphic), lime green, approx. 1.5 mm (0.06 in.) broad; petals 5, very narrow (subulate). Sepals 5. Stamens 5. Gynoecium syncarpous, with 2 styles. Flowers borne in roundish axillary clusters of 4–15.
- Leaves: Lower leaves opposite, upper alternate, stalkless, stipulate. Blade small, elliptically ovate, with entire margins. Stipules small, membranous, different sizes.
- Fruit: Egg-shaped, thin-walled achene, slightly longer than calyx.
- Habitat: Dry sand fields, sandy hillside ridges, sand pits, roadsides, railway embankments, loading areas, wasteland.
- Flowering time: July–August.
Glabrous rupturewort has arrived in Finland in many ways and through many routes, but probably only with people. It grows along the coast of the Åland Islands and as far as Kymenlaakso, and inland it has two habitats in southern Savo and southern Karelia. Stands are located in old culturally influenced areas where there has been contact with the species’ main habitat in Europe. It has stowed away in sailing boat ballast soil and with groups of soldiers, and has perhaps been deliberately introduced as it has been used to treat some special illnesses and sexually transmitted diseases.
Glabrous rupturewort thrives in a wide range of habitats that people have created. It is important that it is in a sunny place because it demands a lot of light and space. Trampling and erosion do not bother the plant, and it can grow even between paving stones down low on the ground. The stem’s upper and lower halves are different, as is often the case with plants that grow horizontally. Glabrous rupturewort flowers very abundantly, and several compact inflorescences give it a lively lime green colour. Despite the modest appearance of the flowers they secrete a lot of nectar and are pollinated by small flies and gnats, and they also self-pollinate too. It produces a lot of seed and spreads easily to new areas. Glabrous rupturewort is often very short-lived: when old habitats get choked up it moves to new places nearby. As land use intensifies and people become tidier it is harder for it to find new habitats, and the plant is thus in decline in Finland.