Sunday, April 6, 2008

Drab (a)? Not really

One of the biggest genera in the mustard world (Brassicaceae) is Draba, or the whitlow-grasses. There are just over 100 species in North America, but nearly all are species of northern tundra habitats and high alpine haunts, or arid places of the western U.S. Here in Ohio, there are only three native species, and all are major rarities. I found all three on my southern Ohio botanical foray last Saturday, and two of them were looking quite nice. The third, Carolina Whitlow-grass, Draba reptans, was not quite ready yet.
This is a classic Adams County shortgrass prairie, and the primary habitat that has put this county on the map botanically. These small prairies are on very thin soil over dolomite limestone, and often have Eastern Red Cedar, Juniperus virginiana, in and around them. They are far older than the tallgrass prairies of western and northern Ohio, is this region was unaffected by the Wisconsin glaciers of 12,000 years ago. Walking into one of these sites is akin to time-traveling back into some of Ohio's oldest habitats, and they are a botanist's dream. These prairies harbor some of the greatest densities of rare flora in the Midwest.

One of my targets, Wedge-leaved Whitlow-grass, Draba cuneifolia. A gorgeous but VERY diminutive plant, and a very early bloomer. Most were in full flower, but a few had already formed fruit, which in mustards are termed siliques, or pods.

A closeup of the basal rosette of leaves of Wedge-leaved Whitlow-grass. The whole thing is probably not even is big as a quarter. Like most little things, though, upon close inspection these mustards are filled with interesting and beautiful detail. You'll have to lay on the ground to appreciate it, though.

My friend John Howard had told me what a fantastic year it is for these rare little mustards, and he was quite right. This one is called Michaux's Leavenworthia, Leavenworthia uniflora. At the sites that I saw it, there were scads in bloom. Two botanists are immortalized in the naming of this one. Dr. Melines Conklin Leavenworth was a U.S. Army surgeon, exlorer, and botanist. The legendary botanist Andre Michaux explored and described many plants from the eastern U.S. in the late 1700's.

A rather cheery looking little plant, and Leavenworthia certainly adds a jolt of brightness to otherwise barren early spring prairies. It, like the other mustards in this post, require very barren rocky or sandy substrates, largely free from competing plants.

Here's an entire plant, in all of its quarter-sized glory. Unlike the simple leaves of our Drabas, Leavenworthia basal rosette leaves are compound, and might remind you of other mustards such as various cresses.

After a suitable period of time admiring the prairie plants, it was on to Sandy-Spring Cemetery. Located right along the Ohio River in southernmost Adams County, this cemetery contains one of rarest and best remaining examples of one of our rarest habitats, an Ohio River sand terrace. The entire bend of the river, including the cemetery, is essentially an enormous pile of sand washed into this inside bend of a huge, sweeping curve of the river. Most of the original sand terraces are destroyed, either by agriculture or outright development. This small cemetery has many rare plants, and a particularly interesting feature is the profusion of Prickly-pear cactus, Opuntia humifusa, which is native here.

Little Whitlow-grass, Draba brachycarpa. This is one of only two known Ohio sites, and amongst the furthest north known sites. I'm not sure anyone has seen the other population in a decade or so. It occurs in a cemetery along the Ohio River in Lawrence County, but that site is far better groomed than is this cemetery, and that is not a good thing for rare plants. This little plant is truly a stunner, but it is REALLY small!

The backdrop of this dime gives a dimensional scale to this tiny plant. This individual was a whopper, too - that's why I chose to photograph it.

While sandy river terraces is the macro-habitat of Little Whitlow-grass, this is the micro-habitat. This mustard is what might be termed a "pioneer", a species that invades newly disturbed openings, grows in profusion for perhaps a few years, peppering the soil with their copious production of tiny seeds. Then, when other plants eventually exclude it, the mustards exist in a dormant yet viable state for many years or decades as seeds in the seedbank, until a traumatic disturbance event re-opens their habitat. Historically this would have been floods; today, disturbance associated with the excavation of graves.
I'm looking forward to repeating this field trip next early April.


Anonymous said...

Cool, I like the picture by the dime, what a neat little plant. - Ben W.

Julie Zickefoose said...

I love this and the prior post about Goldenstar. Knowing you were down on your belly photographing dime-sized plants on a rainy day warms my heart.
Our lawn is carpeted with a small invasive white cress that came in with a load of sandy loam--everywhere! Dreadful! Any idea what it might be? Divided leaf, basal rosette, maybe 2" tall--crowned with a roundish head of white flowers. In the space of four years, it's become our worst weed.
Thanks for these posts, asking us to look more closely, always a great idea.

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