- Latin synonym: Stellaria uliginosa
- Name also: Bog Chickweed (USA)
- Family: Pink Family – Caryophyllaceae
- Growing form: Perennial herb.
- Height: 10–20 cm (4–8 in.). Stem limp–ascending, 4-edged, soft, glabrous, glossy.
- Flower: Corolla regular (actinomorphic), white, approx. 5 mm (0.2 in.) broad; petals 5, deeply 2-lobed (looks like 10 petals), 1–2 mm (0.04–0.08 in.) long, shorter than calyx, sometimes lacking. Sepals 5, glabrous. Stamens 10. Gynoecium syncarpous, with 3 styles. Inflorescence apparently an axillary, 2-branched cyme; subtending bracts membranous, glabrous.
- Leaves: Opposite, stalkless. Blade ovate–elliptic–linearly lanceolate, thickish, glabrous, bluish green, 3-veined, with entire and membranous margins, basal part sparsely haired.
- Fruit: Egg-shaped, yellowish brown, 6-valved, 3–4 mm (0.12–0.16 in.) long capsule.
- Habitat: Edges of springs, spring streams, spring-water ditches, shores, waterside meadows which are prone to flooding and becoming swamps, damp forest roads, sometimes loading areas, planting beds.
- Flowering time: May–July.
Bog stitchwort is quite a southerly plant in the wild in Finland: it is most commonly found in the south-western part of the country in Satakunta and southern Häme and Savo, although they are quite rare at the limits of this border. In keeping with its name, this weak competitor usually grows in springs or other areas that are affected by moving water, either in the water itself or on soft, wet, mossy surfaces. Sometimes it can be found on banks that get sprayed with water, in rich mixed swamps, or on the edges of waterside meadows that are prone to flooding. If its original habitat is dredged or excavated it may retreat to field ditches or damp roadsides. In central Finland and northern Savo they are the species most common habitats, and it seems that it has followed people to these areas. It is known to have spread to Kainuu during WWII with German soldiers.
In suitable places bog stitchwort spreads vegetatively very efficiently. Its inflorescence is quite sparse but it blooms throughout the summer – in unfrozen springs it is possible to see still-open flowers in November. Not many seeds develop, and they have no special tricks to help them spread. The fact that the species is missing from many places that would seem to be suitable such as ditches and streams seems to point to the difficulties it has in crossing even small hurdles. The species has probably jumped from one habitat to another with birds and perhaps water mammals, and with people it has turned up in unpredictable places.
Bog stitchwort looks a bit like fleshy stitchwort (S. crassifolia), but the former’s leaves are thicker and bluish green, and its subtending bracts are membranous. Also, bog stitchwort’s inflorescence is axillary and its flowers are somewhat smaller.