Great Falls grasslands

our fallsSo the last place you would probably expect a workshop on grasses identification to take place would be Great Falls Park. It turns out, however, that the park harbors some specialized habitat—globally rare, according to trip leader Cris Fleming—that is especially hospitable to Poaceae and the other graminoids.

high water marksThe Potomac River’s periodic floods, every twenty or so years, is the key to the grasses’ success. Right along the edge of Mather Gorge, large trees don’t get a chance to establish a closed canopy which would shade the grasses out.

bedrock terraceThe result is tiny patches of specialized plant communities that otherwise you’d expect to see in the tallgrass prairie of the Great Plains. Tucked into the crags and clinging to the extremely thin soil are species like Big Bluestem (Andropogon gerardii), Little Bluestem (Schizachyrium scoparium), and various Panicum species, like Switchgrass. Members of some other plant families like it here, too, like the flashy blue Dense Blazing Star (Liatris spicata), the diminutive Whorled Milkweed (Asclepias verticillata), and Wingstem (Verbesina alternifolia).

no one sowed themIt should come as no surprise that grasses are a challenging photographic subject, especially when the photographer and gear are of the point-and-shoot variety. But I did manage to snap this image of Wild Oats (Chasmanthium latifolium) in a slightly shadier spot.

keying it outOf the fescue tribe of the grass family, we looked at Elymus virginicus, Virginia Wild Rye (not related to the domesticated rye), with its aggresively long awns; Bottle-brush Grass (E. hystrix), looking like a herringbone; Purple-top (Tridens flavum), also known as Greasegrass: it feels more tacky than greasy. North of the visitor center, in the bed of the Potowmack Canal, we saw two Leersia species, including Rice Cutgrass. My old posts suggest that this native plant is a problem at Huntley Meadows Park, but we saw just a small patch here. It does resemble the violently aggressive Stilt-grass (Microstegium vimineum), but its leaf lacks the silvery pale midrib.

We also found some nice examples of non-grasses, a nice sedge (Cyperus strigosus) and a rush all in fruit (Juncus tenuis) ekeing out life on the towpath. Elsewhere, the Black Gums (Nyssa sylvatica) are starting to go red in the leaves. Black Vultures (Coragyps atratus) were kettling and generally hanging out with the more numerous Turkey Vultures.