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FAMILY

Hoary cress is in the mustard family: Brassicaceae (or Cruciferae- the old name)
The family is characterized by four petals (rarely 0 petals) that are white or yellow, and 6 anthers (rarely 2 or 4), with four of them longer and two noticeably shorter.

The Brassicaceae has about 365 genera and 3250 species located all over the world, especially in temperate areas.

GENUS

Hoary cress is in the genus Lepidium, and here are characteristics to help you determine if the mustard plant is hoary cress or not:

1. Leaves are entire to shallowly lobed, and the upper leaves (the ones on the stem - called cauline leaves) are clasping the stem.
2. If there are hairs on the leaves, they are simple (not stellate or branched).
3. Inflorescence is terminal and wider than it is tall.
4. Fruit must be cordate to round or ovate, and inflated perpendicular to the septum (the septum is the wall that divides the two halves of the fruit). Undeveloped fruit may not inflate very much.
5. Fruit is mostly indehiscent, meaning that it usually doesn't pop open to let the seeds out.
6. Two chambers per fruit,and each fruit chamber has 1 or 2 seeds.

Hoary cress can look like other Lepidium, but they differ mostly by having flat fruit (not inflated), and the fruit are dehiscent (they open to let the seed out).

ID CONTACTS

If you are still not sure, contact your county weed supervisor, or send a piece of the plant with fruit on it and the collection location to:

John Gaskin
USDA-ARS
1500 N. Central Ave
Sidney, MT 59270

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