Boechera grahamii (Spreading-pod Rock Cress)

Plant Info
Also known as: Purple Rockcress
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):Minnesota county distribution map
National distribution (click map to enlarge):National distribution map

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Detailed Information

Flower: Flower shape: 4-petals Cluster type: raceme

[photo of flowers] 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: Leaf attachment: alternate Leaf attachment: basal Leaf type: simple

[photo of stem leaves] 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.

[photo of basal leaves] 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 type: capsule/pod

[photo of 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 taken at Long Lake Regional Park, New Brighton, MN and Wild River State Park, Chisago County.

Comments

Have you seen this plant in Minnesota, or have any other comments about it?

Posted by: Deane - Hubbard County
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.

Posted by: Natalie - Minnesota Point, Duluth
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!

Posted by: Jenny K - Rice Lake State Park
on: 2017-05-14 22:59:47

Recently saw this lovely flower at Rice Lake in a marshy area. May 13, 2017

Posted by: Jean G - Pine County - northeast of Pine City
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.

Posted by: K. Chayka
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.

Posted by: Jean G - Pine County
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.

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