Pinnate Tansymustard

Pinnate tansymustard (Descurainia pinnata) is found throughout all of North America. This native annual (or winter biennial) grows in sunny disturbed sites with poor soil up to about 8,000 feet. Variable in appearance, there are as many as ten subspecies. This hardy plant is often considered a noxious weed.

Pinnate tansymustard is a hairy, heavily-branched plant. The stems are green or purple tinged. The alternate leaves are pinntaely dissected.

The pinnate tansymustard inflorescence is a terminal raceme (arrangement of flowers along a stem on individual stalks that are about equal in length). Each individual flower has four yellow to greenish yellow or cream petals that alternate with four yellowish sepals. The style is surrounded by six stamens.

One feature distinguishing pinnate tansymustard from other Descurainia are the fruits. Pinnate tansymustard fruits are siliques (elongated capsules with a septum separating into two valves). In this species the silique pedicels (stalks) are the same length or much longer the siliques themselves. There are two rows of minute seeds in each valve.

This member of the Mustard Family (Brassicaceae) contains nitrates and thiocyanates. In large amounts it it toxic to grazing animals although it can be eaten in small amounts. Pinnate tansymustard seeds were eaten like pepper by Native Americans or ground and used to treat stomach ailments. They also consumed the foliage.

The genus name honors Francois Descurain (1658 – 1740), a French botanist and pharmacist. In Latin the specific epithet means “feather” and describes the finely cut leaves. Western tansy mustard and yellow tansymustard are other common names for D pinnata.

These pinnate tansymustard plants were photographed in May in one of our pastures near Lookout CA (Modoc County).

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