Boechera grahamii (Spreading-pod Rock Cress)
|Also known as:||Purple Rockcress|
|Life cycle:||biennial, short-lived perennial|
|Habitat:||part shade, sun; sandy soil, prairies, open woods|
|Bloom season:||May - July|
|Plant height:||10 to 40 inches|
|Wetland Indicator Status:||GP: FACU MW: FACU NCNE: FACU|
|MN county distribution (click map to enlarge):|
|National distribution (click map to enlarge):|
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Flowers are in raceme clusters that elongate over time, at the top of the plant and on stems arising from leaf axils in the upper part of the plant. Individual flowers are about ¼ to 1/3 inch across with 4 spreading white petals and yellow stamens, on stalks ½ to 1 inch long.
Leaves and stem:
There are both basal and stem leaves. Stem leaves are hairless and toothless, average about 1½ inches long and less than ¼ inch wide, with a pointed tip and usually 2 lobes at the base that appear to clasp the stem. They are mostly erect.
Basal leaves are more spoon or spatula shaped, are covered in split coarse hairs, giving them a rough texture, and may have a few shallow teeth around the edges. The main stem is mostly hairless, except near the base, and is sometimes purplish.
Fruit is a narrow pod up to 3 inches long containing 1 or 2 rows of seeds. The pods are mostly straight and horizontal, but may be somewhat ascending, descending, or bowed. They ripen to a purplish color and a large fully ripe plant may take on a bushy appearance.
Spreading-pod Rock Cress is not an uncommon plant by any means, yet it was surprisingly difficult to ID. It isn't listed in any of my field guides or other print references, nor is there much info about it on the web. I wasn't sure this was it until I looked at a herbarium specimen. There are several species of Rock Cress in Minnesota; they are distinguished by the shape of the leaves or cluster, and/or the shape or positioning of the fruit. Most were in the Arabis genus, but many have since been shuffled around to other genera. Spreading-pod Rock Cress formerly was known as Arabis divaricarpa.
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Photos by K. Chayka taken in Chisago and Ramsey counties. Photos by Peter M. Dziuk taken in Anoka County.
Have you seen this plant in Minnesota, or have any other comments about it?