Boechera retrofracta / reflexed rockcress

Adjectives: early spring, exposed, interesting bits, native, rocky

Also known as: secund rockcress
Synonyms: Arabis secunda, Turritus retrofracta, Arabis holboellii var. retrofracta

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Reflexed rockcress is a biennial or short-lived perennial in the mustard family.  As far as I can tell, it is rather uncommon (although, in June 2023, I’m finding lots of it along the Victor/Driggs bike path just south of 3000). Unlike some others in the family, the flowers (although quite small) are attractive and a bit unusual. Basically, they are white or light lavender and bell-shaped. They grow on a single stem (raceme). At anthesis, i.e. when they are mature and shedding pollen, they hang down close to the stem. There can be a huge number of flowers on a single stem, up to 80 and sometimes even more.

Once the fruit are formed, siliques, these are also pendent, a.k.a. strongly reflexed. This is one clear difference between this and tower mustard (Turritus glabra) but the similarity of the siliques must be why this species was once included in the genus Turritus. And the fact that the siliques are sometimes secund (all on one side of the stem) is reflected in another of the old names for the species.

Like other mustards, reflexed rockcress grows from a rosette. The basal leaves and the lower stem are densely hairy (pubescent) and elongated. The leaf margins are sometimes slightly toothed.

As the name might suggest, reflexed rockcress is usually found on rock outcrops…  or on open hillsides, or gravel bars, and often near sagebrush (probably reflecting its drought tolerance). In the Valley, I’ve so far only seen it only on a  rock outcrop in a sagebrush community.

Interesting bits – There is very little folklore (i.e. none) regarding this species and it would not be unexpected for it to be uninteresting to anyone but a few systematist/taxonomist sorts. But because Boechera retrofracta has formed hybrids with at least 12 other species (e.g. this paper), it has actually received more attention at the molecular level. It is considered closely related to the only “model” species that most molecular biologists think about, Arabidopsis thaliana (mouse-eared cress), but the genus Boechera contains both sexual and apomictic species. B. retrofracta is diploid and sexually reproducing but may be an ancestral parent of the apomictic species (Original paper).