Sagina nodosa (Knotty Pearlwort)
|Also known as:||Knotted Pearlwort|
|Habitat:||part shade, sun; bedrock shore of Lake Superior|
|Bloom season:||June - August|
|Plant height:||3 to 8 inches|
|Wetland Indicator Status:||GP: none MW: none NCNE: FACU|
|MN county distribution (click map to enlarge):|
|National distribution (click map to enlarge):|
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Flowers are borne singly at the tips of slender branching stems. Individual flowers are ¼ to 1/3 inch across, typically with 5 white egg-shaped petals (sometimes 4), with 5 styles on the yellowish ovary in the center, surrounded by 10 slender white stamens. The 5 green sepals are about half as long as the petals, and tightly pressed against them with their rounded tips exposed between the petals.
Leaves and stems:
Leaves are mostly basal, ¼ to 1 inch long, needle-like with smooth surfaces, triangular in cross section, in a dense tuft. Leaves on flowering stems are opposite and scale-like. Stems are erect to spreading, branching on the upper plant, typically reddish brown, wiry and smooth or with sparse, short glandular hairs on flower stalks and at the base of the calyx.
Fruit is an upright capsule, tightly enclosed by the reddish sepals, with five triangular, spreading teeth when open.
Sagina nodosa is a circumboreal species divided into a European subspecies - ssp. nodosa - that enters into North America along the north Atlantic coastline as far south as Massachusetts. The North American ssp. borealis inhabits moist sandy or rocky shores of inland lakes from the subarctic to the Northshore of Minnesota and the upper peninsula of Michigan. Found at only a few fragile sites in Lake and Cook counties where it is threatened by both human and seagull activity, it was listed as endangered by MNDNR in 1984. Interestingly it is strikingly similar to another rare Minnesota native in the same family, Rock Sandwort (Minuartia dawsonensis), which is restricted to dry sedimentary rock outcrops and is presently listed as threatened.
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Photos by K. Chayka and Peter M. Dziuk taken on the north shore of Lake Superior, Lake County.
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