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Perennial of the Gentianaceae family, the marsh gentian is widely spread in Europe, from the Iberian Peninsula to Western Siberia. It is not a mountain plant but a lowland and low altitude species, confined to wet heaths, transition bogs, poor acidic meadows, and ditch edges, on poor, acidic, and constantly fresh to moist soils.
It forms upright clumps of 20 to 40 cm, with slender stems bearing very narrow, dark green, sessile, opposite linear leaves, almost grass-like in appearance, giving it a light and slender silhouette quite distinct from alpine gentians.
The flowers, borne in the axils of the upper leaves and at the top of the stems, are tubular-campanulate, of an intense blue to deep blue-violet, with five erect barely spreading lobes and pale green to greenish dots inside the tube, visible at the corolla's opening. The color is among the most saturated blues of the genus.
In its natural habitat, its flowering extends from July to September. In cultivation, it blooms from August to October depending on conditions.
Protected species in several European countries due to the decline of wet heaths, it is also the sole host plant of the Maculinea alcon butterfly caterpillar, making it a key species in certain ecosystems. In cultivation, it requires an acidic, poor, constantly moist soil, in full sun; it poorly tolerates competition from vigorous plants.