Arenaria serpyllifolia (Thyme-leaved Sandwort)
|Also known as:|
|Habitat:||part shade, sun; disturbed sandy or gravelly soil; roadsides, waste areas, fields, lawns|
|Bloom season:||May - September|
|Plant height:||2 to 16 inches|
|Wetland Indicator Status:||GP: FACU MW: FAC NCNE: FAC|
|MN county distribution (click map to enlarge):|
|National distribution (click map to enlarge):|
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Stalked flowers in small clusters at the tips of branching stems, as well as single in the leaf axils. Flowers are about ¼ inch across with 5 egg-shaped petals, 10 white-tipped stamens and a green ovary in the center with 3 styles at the tip. Alternating with the petals are 5 hairy sepals that have a long, tapering point to the tip and are typically longer than the petals. Flower stalks are initially short but elongate to about ½ inch in fruit.
Leaves and stems:
Leaves are ¼ to 1/3 inch long, up to 1/6 inch wide, toothless, egg to teardrop shaped with sharply pointed tips and no stalk. Surfaces are mostly hairless but there are tiny hairs all around the edges. Leaves are initially crowded on the stem, but spread out as the plant matures, becoming widely spaced by fruiting time. Stems are multiple from the base, heavily branched, erect to sprawling, and can form a tangled mat or have a bushy appearance.
Thyme-leaved Sandwort is very likely an under-reported weed in Minnesota, since it's small and tends to inhabit areas that are weedy with other species. While the leaf and stem arrangement may resemble some Chickweeds (Cerastium and Stellaria species), those have flowers with 5 petals that are deeply notched or divided. The flowers more closely resemble other Sandworts (Moehringia spp.), which have much longer leaves, plus flowers that are less star-shaped, with oblong-elliptic petals. There are 2 varieties of Arenaria serpyllifolia, though they are not universally accepted, and both of which are introduced species: var. tenuior, with cylindrical fruits and mostly found in the southeast quadrant of the US, and var. serpyllifolia, found in most US states, including Minnesota, and into Canada.
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Photos by K. Chayka and Peter M. Dziuk taken along a bike path near Seminary Fen SNA, Carver County, and the driveway to Pine Bend SNA, Dakota County.
Have you seen this plant in Minnesota, or have any other comments about it?