Subspecies
Common Marsh Bedstraw (Common Marsh-bedstraw, Lesser Marsh Bedstraw, G. palustre ssp. palustre), Great Marsh Bedstraw (Great Marsh-bedstraw, G. palustre ssp. elongatum).
Also classified as independent species, Galium palustre (Lesser Marsh Bedstraw) and Galium elongatum (Great Marsh Bedstraw)
Growing form
Perennial herb.
Height
10–50 cm (4–20 in.). Stem limp–erect, delicate, usually 4-edged, glossy–rough.
Flower
Corolla shallowly funnel-shaped, white, approx. 3–5 mm (0.12–0.2 in.) broad, fused, 4-lobed. Calyx lacking. Stamens 4, anthers red. Pistil of 2 fused carpels, styles 2. Inflorescence a broad, lax, many-parted cyme.
Leaves
Regular (actinomorphic), usually 4 (sometimes up to 6) whorled leaves; stalkless. Blade elliptic–lanceolate–loblanceolate (ssp. palustre), broadly elliptic–oblanceolate (ssp. elongatum), round-tipped, lacking bristle, thin, glabrous, with entire margin, revolute.
Fruit
2-parted or almost round (one half undeveloped), glabrous schizocarp.
Habitat
Sea and lake shores, stream banks, ditches, swamps, damp meadows.
Flowering time
June–August.

The Bedstraw family is one of the largest in the plant kingdom: it has over 13,000 members and is still growing, in Finland too. Marsh bedstraw is a very diverse plant across its wide habitat. Part of the variation is due to their polyploid nature, meaning that they have more than two paired (homologous) sets of chromosomes. Of the plant’s subspecies, ssp. palustre has the regular two pairs of chromosomes: one of the homologous chromosomes carries the male hereditary line when it is fertilised by pollen, the other carries the female like. Compared to this, ssp. elongatum, which is larger, has no fewer than a four-fold complement of chromosomes. Such a large difference shows not only in the size of the plant but also in its appearance: ssp. elongatum has longer internodes and broader leaflets. Even small deviations in the chromosomes cause at least severe development difficulties and disabilities in humans and animals, but in plants even bigger changes are part of the normal development of species.

Not all the variations between different strains of marsh bedstraw can be explained by its polyploid nature, however. The constantly rising land around the Baltic Sea has provided the preconditions for new species to appear. The Baltic species var. balticum only grows on land that has recently risen from the sea. Its stems are almost glossy, its leaves are short and narrow, and it produces more seed than its close relatives.

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