Comarum is a small genus of flowering plants in the rose family (Rosaceae), placed in the order Rosales. It was described by Linnaeus in 1753 and contains one or two species: marsh cinquefoil, Comarum palustre, is the type and, by most accounts, the only widely recognized member, while a second segregate, Comarum salesowianum, is sometimes instead treated as the monotypic genus Farinopsis. For much of the twentieth century the genus was subsumed within the related genus Potentilla (the "cinquefoils"), and it is still occasionally encountered under the synonym Potentilla palustris in older or regional references.
Plants in the genus are waterside, rhizomatous subshrubs with sprawling, vine-like stems that can trail a metre and a half or more, rooting wherever they touch wet ground. The compound leaves are glaucous green with three to seven, usually five, narrow, coarsely toothed leaflets. Flowers are borne in loose terminal clusters and are unusual within the rose family for their deep red-to-purple coloring, with five (occasionally six) large sepals and smaller, darker petals surrounding a ring of spatula-shaped stamens; the fruit resembles a small dry strawberry — a resemblance echoed in ornamental hybrids produced by crossing Comarum with the strawberry genus Fragaria.
Comarum favors peaty, boggy, or otherwise waterlogged ground: lake shores, marshy riversides, and stream margins across the cool temperate and boreal Northern Hemisphere, with a circumboreal distribution spanning North America, Europe, and Asia. Plants often grow partly submerged, with foliage floating on the water surface.
Distribution
Comarum has a circumboreal distribution across cool temperate and boreal regions of North America, Europe, and Asia.
Ecology
Plants grow on lake shores, marshy riversides, and stream margins, often partly submerged with their foliage floating on the water surface — reflecting the genus's preference for peaty, waterlogged ground.
Cultivation
Marsh cinquefoil prefers peaty soils but also tolerates moist sandy ground, and is hardy across USDA Zones 3–9.
Cultural Uses
Comarum has been crossed with the strawberry genus Fragaria to produce ornamental Fragaria × Comarum hybrids, grown for their distinctive red-to-purple flowers.
Taxonomy Notes
Comarum was formerly included within the genus Potentilla and is still sometimes found under the synonym Potentilla palustris. The genus's circumscription is unsettled: it is treated as containing one or two species, with the segregate Comarum salesowianum sometimes placed instead in the monotypic genus Farinopsis. GBIF treats Comarum L. (Rosaceae, Rosales; published in Species Plantarum, 1753) as accepted, with two descendant taxa in its backbone.
