Davis’ Knotweed

Davis’ knotweed (Aconogonon davisiae) grows amid talus or on rocky sites where snow accumulates between 5,000 and 10,000 feet in Oregon, Washington, California and Idaho. Leonard and I found these Davis’ knotweed plants in August near the Lassen Peak Trailhead in Lassen Volcanic Park CA.

A native perennial, Davis’ knotweed arises from a long taproot. The deep taproot helps the plant tolerate drought. The several spreading to ascending stems are often red.

The simple, alternate leaves are lance-shaped to round and glaucous (coated in a waxy powder that can be wiped off). A brown-red, papery ocrea (stipules fused into a sheath around the stem) surrounds each leaf. In the fall the stems and leaves turn a bright red.

Davis’ knotweed flowers occur in groups of 2 to 5 in the leaf axils. This flower has no true petals, but the five sepals resemble petals and are yellowish to green and often tinged with purple. The ovary is superior and there are 8 stamens. The fruits are smooth, light brown, achenes (single dry seed that does not split open).

Davis’ knotweed is a member of the Buckwheat Family (Polygonaceae). A synonym for A davisiae is Polygonum davisiae. Nancy Jane Davis (1833-1921), an educator and plant collector who first collected specimens of this plant, is honored by the species designation. The genus, Aconogonon, is from Greek (“akonao”/ to sharpen and “gonia”/corner or angle) and refers to the sharp edges of the fruits.

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