Boechera grahamii (Spreading-pod Rock Cress)
Also known as: | Purple Rockcress |
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Genus: | Boechera |
Family: | Brassicaceae (Mustard) |
Life cycle: | biennial, short-lived perennial |
Origin: | native |
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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Detailed Information
Flower:
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:
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.
Notes:
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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More photos
Photos by K. Chayka taken in Chisago and Ramsey counties. Photos by Peter M. Dziuk taken in Anoka County.
Comments
Have you seen this plant in Minnesota, or have any other comments about it?
on: 2013-06-04 23:52:50
I believe this is the rock cress growing on our dry roadside on excessively drained, gravelly soil in full sun.
on: 2015-01-19 12:37:36
Blooming in late June in sandy soil on Minnesota Point. I had the same trouble with ID - it's pretty distinctive looking, but I struggled to find any information. Glad to see it here!
on: 2017-05-14 22:59:47
Recently saw this lovely flower at Rice Lake in a marshy area. May 13, 2017
on: 2017-05-15 15:10:42
The new plants in the sandy rocky fields surrounding our house appear to be rock cress. They were a surprise in the past 2 weeks. They are now blooming and seem to be spreading rapidly. I was concerned they were invasive and had a very hard time finding information to make an accurate identification.
on: 2017-05-15 16:09:50
Jean, there are several species of rockcress and none of the natives are what I would consider invasive, creating anything resembling a monoculture. Your perspective may be different, of course.
on: 2017-05-16 10:05:46
I should have made my previous comments more specific. Once I identified the plants as rock cress I felt delighted to have them. They are most certainly Boechera grahamii. This site was quite helpful to me.
on: 2018-05-26 10:23:46
Growing in savanna prairie in Radio Dunes area of Carlos Avery Sunrise Unit. Fairly common. In full flower prior to seed set.
on: 2020-06-04 19:03:58
Growing here in Uncas in sandy areas. Have noticed Olympia Marble butterfly hanging out on these a lot in late spring and it turns out it's a larval host plant.
on: 2024-05-27 06:33:58
Found this growing all along the Paul Bunyan bike trail near Bemidji. This one had my stymied for I.D., as the form looks like a Penstemon, but only 4-petalled flower! iNat gave an I.D. of rock cress, and your site helped me confirm it!