Scleranthus annuus (Knawel)

Plant Info
Also known as: German Knotgrass, Annual Knawel
Genus:Scleranthus
Family:Caryophyllaceae (Pink)
Life cycle:annual
Origin:Eurasia
Status:
  • Weedy
Habitat:sun; dry disturbed soils; sandy ditches, old fields, waste places, lawns
Bloom season:May - September
Plant height:2 to 5 inches
Wetland Indicator Status:GP: FACU MW: FACU NCNE: FACU
MN county distribution (click map to enlarge):Minnesota county distribution map
National distribution (click map to enlarge):National distribution map

Pick an image for a larger view. See the glossary for icon descriptions.

Detailed Information

Flower: Flower shape: 5-petals Cluster type: panicle

[photo of flowers] Flowers are small, about 1/8 inch across, very profuse in dense, rounded clusters at the tips of forking branches, lacking petals but with 5 petal-like sepals, green with a narrow band of white around the edge, lance-triangular with pointed tips. In the center are 2 filament-like styles and 2 to 10 yellow stamens. The calyx-like base (hypanthium) is angled, about as long as the sepal lobes.

Leaves and stems: Leaf attachment: opposite Leaf attachment: whorl Leaf type: simple

[photo of leaves] 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.

[photo of stem hairs] Stems are hairless to minutely hairy, spreading to ascending, profusely branching, often forming compact mounds up to 5 inches across. The whole plant is a bright, light green.

Fruit: Fruit type: capsule/pod Fruit type: seed without plume

[photo of developing fruit] Fruit is a small inflated “urticle” contained within the persistent, drying hypanthium, containing a single yellowish seed. The persistent sepals are mostly erect in fruit.

Notes:

Knawel is an Old World species that has become established nearly world wide, likely through just accidental introductions. It is common throughout much of the eastern US and on the west coast. Minnesota's first collection was in Winona in 1889. Because of its diminutive size, it's likely always been under-reported, but it's just been in the past 20 years it's been appearing more widely in our state. It is very drought tolerant and is mostly associated with very dry, sandy disturbed sites and may or may not become a problem in sensitive and rare sand dune habitats. It is easily recognizable from the mound of tiny, star-shaped flowers that have green petal-like sepals with pale edging, and the linear, opposite leaves. There are apparently several subspecies, but they are not well documented except for subsp. annuus, which is described above and the species found in Minnesota. Interestingly a tincture of its essence is being marketed as a treatment for those suffering from indecision, lack of poise and balance. I can't decide if I should try it or not...

When we first published this species, we mistakenly included images we believed were annual Knawel, but were actually Perennial Knawel (Scleranthus perennis), which turned out to be a new state record. 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 light green over all and sepals are 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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More photos

Photos by K. Chayka and Peter M. Dziuk taken in Pine County.

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