Thursday, August 21, 2014

Two Rare Botanists on a Witch (grass) Hunt


Dichanthelium is "perhaps the most complex and confusing genus in our region" (1). 

Sometimes a mere one tenth of a millimeter difference in a critical measurement can separate two taxa!
For obvious reasons, most folks avoid these smallish and difficult to identify grasses (do you have a micrometer handy?).

But Johnny Townsend of VA Natural Heritage Program (below right) and Richard LeBlond  (right) (formerly of NC Natural Heritage Program) are hardcore enough not to be afraid of the Witchgrasses!

I had the unexpected pleasure to show them around to a few sites in Durham County recently. 

Johnny rarely travels to NC; the Commonwealth keeps him quite busy. 

Richard told me he had never really botanized in the Piedmont before.  

But they came & hopefully will both return!

On this day it was a quest for rarities; mostly taxa that Richard had either named or is working on, and that had been showing up in VA recently. We all hoped they would turn up on one or more sites nearby as well!

After a brief orientation, including review of some pressed specimens Johnny had brought along, Herb & Pat Amyx, Thomas Blaine, and the rest of us headed off in search of live material.  I found it difficult to train my eye to seperate the Dichantheliums from the other vegetation. More difficult was rapidly distinguishing the common species at a mere glance, like Richard and Johnny were able to do.

After traipsing by 7 or 8 other taxa in the genus, innumerable other native species, and just as the sun and humidity seemed to be peaking, Johnny dropped to one knee in front of Ringed Witchgrass (D. annulum). One of our targets was found! Was it the humidity or the excitement that made my legs buckle slightly?

Dichanthelium annulum displaying "autumnal" growth

Ringed Witchgrass was given its currently accepted name in a publication by Richard LeBlond in 2001 (2), elevating it from its former genus Panicum (along with a host of others).

Dichanthelium annulum is considered "significantly rare" in NC. Records have been documented from 15 locations around the state, but only 2 are considered extant in the Natural Heritage Program database (the other locations are historic, meaning they have not been observed for decades).

The bulk of the historic reports are from Piedmont counties including Person, Orange, Wake, and Durham (no apparent coastal plain records but Richard has just informed me of a collection from Roanoke Island!). The habitat has been listed in Weakley's flora as "dry sandy or rocky soil of open woods, dry grasslands, and barrens and glades..." Our site was in a frequently burned, open oak-hickory woodland, on rich clayey soils, with a diverse native ground cover.

Several stems of D. annulum rising above
Partridge Pea (Chamaecrista fasciculata), Earle's Blazing Star (Liatris squarrulosa),
Maryland Senna (Senna marilandica), and others
Most stems of Ringed Witchgrass were relatively tall (over 12") and showed the remains of spring culms and panicles. Roughly 1/3 of the way up the stem were tufts of new leaves slightly hiding newly developing branches or panicles. We found plants in several locations in the first site visited, usually in places where taller plants seemed to be less frequent. With this find, we can once again consider D. annulum "extant" in Durham County. 

After continued traipsing and hunting we visited another site. It wasn't long before Johnny made the second significant find of the a relatively bare patch of rich soil, exposed by recent spring prescribed fire.

Given the local conditions, this taxon was easier to see but harder to explain taxonomically. Currently treated as Northern Witchgrass (Dichanthelium boreale), but also indicated as Panicum bicknelli (1) Richard is working toward a nomenclature change that will treat this as Dichanthelium bicknelli. Regardless of the taxonomy, the plants found are also considered "significantly rare" in North Carolina.  If all the existing records are assigned to the same taxon, this will constitute the 13th or so record in the state, most of which seem to be considerably west of Durham, mostly in the mountains.

Very similar habitat (although not co-occurring) to Ringed Witchgrass, but overall, a much different appearance. These plants were much more clumpy than D. annulum with abundant, sturdier, basally disposed leaves.  An obvious rosette was present (below, left): perhaps these will be the overwintering leaves present in many species? Numerous flowering culms were present (below, right).


(1) Weakley, A. S. 2012. Flora of the Southern and Mid-Atlantic States
(2) LeBlond, R.J. 2001. Sida 19: Taxonomy of the Dichotoma Group of Dichanthelium (Poaceae)


Richard LeBlond (right), "bowing down" before a rare specimen of (soon to be) Dichanthelium bicknelli. 

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