Sunday, April 22, 2012

Draba reptans

This year's March warmth hurried the flowering of many of our spring-blooming forest species, but it also affected some of our early species of open habitats, including the (apparently) very rare Draba reptans, or common whitlow-grass. Draba reptans is a tiny annual mustard of open sandy or gravelly soil, including remnant oak savanna and hillside prairies. These specimens were photographed on an open, historically grazed gravelly ridge in Washtenaw County, where plants occurred in gravelly, loose soils and in sandy pockets between tufts of native prairie grasses. This site, discovered in March, is only the second confirmed record since 1935, the last discovered record dating to the mid-1980s. 

This delicate annual features fruits that are nearly uniformly wide from the base to apex. I used no coin for perspective, but the petals average only 3-4 mm long, and the hairy basal rosette is approximately the size of a dime. The small, inconspicuous nature of this species, its early bloom time, and its often unremarkable habitat conspire to hide its presence from the botanical community, and it appears likely there are more populations in Michigan waiting to be discovered. Exploration of sandy, gravelly kames, eskers, and moraines in southern Michigan is warranted, particularly areas that feature red-cedar (Juniperus virginiana), common juniper (J. communis), and prairie grasses.

This wide-ranging species is apparently secure in most of its range, but the species is generally rare in the eastern portion of its range, and is considered possibly extirpated in Massachusetts, Rhode Island, New Jersey, Pennsylvania, and North Carolina. Approximately 12 populations have been documented in Michigan (Michigan Natural Features Inventory data).


Justin R. Thomas said...

Hey! Is that coin reference casting aspersions my way? It hurts. It really hurts.

That is a sweet little mustard; and by sweet I mean delicious. I've never seen this species, but I am a huge fan of Draba in whatever evolutionary expression they grace this fruitful planet.

Bradford Slaughter said...

Ha- it's actually the realization that scale matters.