Scleranthus perennis (Perennial Knawel)
|Also known as:|
|Habitat:||sun; dry sandy or gravelly soil; roadsides, railroads, waste areas, dunes|
|Bloom season:||June - September|
|Plant height:||2 to 5 inches|
|Wetland Indicator Status:||none|
|MN county distribution (click map to enlarge):|
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Flowers are small, about 1/8 inch across, very profuse in dense clusters at the tips of forking branches, lacking petals but with 5 petal-like sepals, green with a broad band of white around the edge, lance-elliptic with rounded tips. In the center are 2 filament-like styles and 5 to 10 yellow stamens. The calyx-like base (hypanthium) is angled, about as long as or shorter than the sepal lobes.
Leaves and stems:
Leaves are simple and opposite, linear to awl-like, 1/8 to 1 inch long, often slightly curved, toothless, stalkless with a membranous sheath that has fine hairs along the edges. Opposite pairs are joined at the base and arranged at right angles to the pair above and below. Leaves may be crowded at the nodes, almost appearing whorled, especially on young plants. Stems are hairless to minutely hairy, spreading to ascending, profusely branching, often forming compact mounds up to 5 inches across. The whole plant is bluish-green.
Fruit is a small inflated “urticle” contained within the persistent, drying hypanthium, containing a single yellowish seed. The persistent sepals are erect and often curving inward in fruit.
Perennial Knawel is an introduced, Old World species that is not very widespread in North America—Wisconsin seems to be the hotbed so it was only a matter of time before it made an appearance in Minnesota. It was seen as early as 2002 near a restoration planting in Lino Lakes, Anoka County. The seed was likely unintentionally introduced in the soil or seed mix or transported by construction vehicles. It was assumed to be the more common Annual Knawel (Scleranthus annuus) until someone in the know from Wisconsin set us straight (thanks!). So this is a new state record. The two species are distinguished in a couple ways: Perennial Knawel is more blue-green over all and flower sepals are more rounded at the tip with a wide band of white edging so they are more white than green, where annual Knawel is bright green over all and sepals are more triangular and pointed at the tip, more green than white. Otherwise, the plants are very similar in size and form, except of course one is an annual and the other perennial.
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Photos courtesy Peter M. Dziuk taken in Anoka County.
Have you seen this plant in Minnesota, or have any other comments about it?