- Name also: Meadow Starwort (USA)
- Family: Pink Family – Caryophyllaceae
- Growing form: Perennial herb.
- Height: 15–35 cm. Stem ascending–erect, sparsely branched, 4-edged, glabrous, glossy or sometimes lower part slightly rough.
- Flower: Corolla regular (actinomorphic), white, approx. 12–20 mm (0.48–0.8 in.) broad; petals 5, deeply 2-lobed (looks like 10 petals), 6–13 mm (0.24–0.52 in.) long, longer than sepals. Sepals 5, glabrous, broadly membranous margins, clearly 3-veined. Stamens 10. Gynoecium syncarpous, with 3 styles. Inflorescence a 2–12-flowered, usually lax, 2-branched cyme; subtending bracts membranous, glabrous.
- Leaves: Opposite, stalkless, spreading, ascending oblique. Blade narrowly lanceolate–elliptic, glabrous, 1-veined, with entire margins, often bluish green.
- Fruit: Ovoid, yellowish brown, 6-valved, 7–9 mm (0.28–0.36 in.) long capsule.
- Habitat: edges of and hedgerows by waterside meadows that are prone to flooding, springs, streams, ditch banks.
- Flowering time: June–August.
Marsh stitchwort’s white flowers rise up between sedge and grass and dot the green of the waterline in the south of Finland, as far north as Oulu and Kajaani. It doesn’t seem to be a very common plant anywhere, but is most abundant on the south and south-western coastline. It favours damp places such as waterside meadows that are prone to flooding and rich, open bogs, as its scientific name palustris (from the Latin paluster, meaning “of the marsh”) suggests.
Marsh stitchwort is completely hairless as far as its membranous subtending bracts and the flower’s sepals. Lesser stitchwort (S. graminea) looks similar but it has slightly smaller flowers, and the leaves have hairy edges. Greater stitchwort (S. holostea) also looks a bit like marsh stitchwort, but its leaves are clearly fused in pairs at its base. Additionally, these two species favour a clearly drier habitat.
Although it is usually quite easy to classify marsh stitchwort, it has many mutations. These forms are mixed up across its whole habitat, but different forms are more prevalent in different parts of the country. This diverse species was earlier observed to be comprised of two separate plants, so S. fennica was classed in a species of its own (earlier S. palustris ssp. fennica). It can be very difficult to differentiate between these two species: S. fennica often has needle-like leaves which are clearly rough and more winged than its relative’s. The surest identification markers are unfortunately only visible through a microscope.