Semi-desert.  Shrublands, woodlands, openings. Spring. 
Canyons of the Ancients National Monument, March 27, 2005 and April 21, 2016.

Tiny can be terrific.  Early spring in the semi-desert country of the Four Corners finds carpets of Tomostima cuneifolia in Pinyon/Juniper forests.  Tomostima cuneifolia is easily confused with Noccaea fendleri but a close look shows clear differences: notice especially T. cuneifolia's wedge-shaped basal leaves, nearly leafless flower stem, shorter height, and elliptical seed pods.

The Draba genus was named by Linnaeus in 1753 and Draba cuneifolia was named by Thomas Nuttall in 1838 from a specimen collected in Kentucky by Professor C. W. Short.  (Professor Short was honored by William Jackson Hooker as one of the two best botanical collectors from whom he had received specimens.  See the fifth paragraph in the biographical entry about David Townsend, the other collector honored by Hooker). Research published by Al-Shehbaz in 2012 placed this species in the genus Tomostima.  

"Draba", Greek for "acrid", was a name applied to similar Mustards known to the Greeks thousands of years ago.  "Cune" is Latin for "wedge", referring to the leaf shape. I cannot yet find the meaning of "Tomostima".

Semi-desert.  Shrublands, woodlands, openings. Spring.
Canyons of the Ancients National Monument, March 27, 2007.

As the above left photograph with the ruler shows, basal leaves glisten as if they were glabrous (smooth), but as the photograph at left shows, they glisten because of the bright reflection of light from hundreds of tiny stellate (starburst-like, branched) hairs.  You can best see the stellate shape of the hairs at the upper and lower right edges of the leaves. Also see the hairs at the edge of the leaves in the last two photographs below of Tomostima reptans.

Also notice the slight notch, like a tiny thumb on a mitten, on the leaves -- especially apparent on the two larger leaves at three and six o'clock. As discussed below, these tiny notches are one of several key characteristics that separate Tomostima cuneifolia from its look-alike cousin, Tomostima reptans.

Semi-desert.  Shrublands, woodlands, openings. Spring.
Canyons of the Ancients National Monument, March 27, 2005.

Below a fluff of white flowers, green seeds emerge.

Semi-desert.  Shrublands, woodlands, openings. Spring.
Canyons of the Ancients National Monument, May 8, 2007.

Tomostima reptans is very similar to Tomostima cuneifolia in size, flower and seed appearance, most hairiness, and habitat. See below for differences.

This species was at first named Arabis reptans by Lamarck in 1783. Fernald renamed it Draba reptans in 1934 and Al-Shehbaz changed it to Tomostima reptans in 2012. "Reptans" is from the Latin for "crawling".

Semi-desert.  Shrublands, woodlands, openings. Spring.
Canyons of the Ancients National Monument, May 8, 2007.

A number of subtle characteristics help separate Tomostima reptans from Tomostima cuneifolia
1) The Flora of North America gives one key characteristic: "The rachises and pedicels of D. reptans are usually glabrous (rarely with a few isolated trichomes); those of D. cuneifolia are always densely pubescent". 
2) Draba reptans' basal leaves are most often not notched whereas the basal leaves of D. cuneifolia leaves are often notched.
3) The seed pods of D. reptans are grouped fairly tightly in a nearly vertical posture; the pods of D. cuneifolia are in a more open, spreading posture.
4) The upper portion of the stem of D. reptans is usually glabrous versus the hairiness of the upper portion of the stem of D. cuneifolia.
5) The seed pods of D. reptans are rarely over 2 millimeters wide; those of D. cuneifolia are often over 2 mm wide.
6) The seed pods of D. reptans are up to 20 mm long; those of D. cuneifolia do not exceed 15 mm in length.

Semi-desert.  Shrublands, woodlands, openings. Spring.
Canyons of the Ancients National Monument, April 9, 2012 and April 18, 2010.