Exploring the Millboro Shale Formation: A Treasure Hunt for Endemic Plants

I had been wanting to make a trip to Bath County to explore shale-barrens for a couple of years, so I was very excited to finally be visiting one.  Drew and I climbed up a steep slope, trying not to dig our feet into the loose shale too much, towards the light green of the herb layer ahead.  The canopy opened up around us as we neared the top of the mountain.  The only trees in site were gnarled old eastern redcedars growing out of the rocky ground, and the occasional chestnut oak, northern red oak or Virginia pine.  Large rock outcroppings pierced the shaley ground, covered in blunt-lobed woodsia and rock spikemoss.  Would we find what we were looking for?

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Shale-barren in Bath County.  Note the shale-barren wild buckwheat (the big fuzzy leaves and stalks growing on the center of the big rock).

Shale-barrens occur on hot, dry, south facing slopes in the Mid-Atlantic states of Pennsylvania, Maryland, West Virginia and Virginia.  They are characterized by shaley soils, with many small pieces of broken up shale on the surface of the ground.  Shale-barrens are too dry for most tree species to grow, leading to a very sparse, open canopy.  However, many species of herbaceous plants are specifically adapted to shale-barrens, growing in no other habitats.  These shale-barren endemics are confined by the small range of their habitat, so many of them have relatively few populations, making them vulnerable to extinction.

Two of the shale-barren endemics I was most excited about seeing were the white-haired and Millboro Leatherflowers (Clematis albicoma and C. viticaulis respectively).  Both occur only on shale-barrens, C. albicoma only in Virginia and adjacent West Virginia, and C. viticaulis only in Bath, Augusta and Rockbridge Counties in Virginia.  They are both small, semi-woody plants.  They have opposite rounded leaves, beautiful drooping flowers and incredible spiraled seed-heads.

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Clematis albicoma seed-head in its full glory.

On our drive out, we had watched the road bank for interesting flowers on the long, winding road in Bath County.  Suddenly a splash of pink appeared, perhaps a phlox of some type?  We marked the spot in our memory so we could check it out on the way back.  We passed several places where the road banks were covered in loose shale flakes, telling us we were now on a shale formation.

Once we emerged from the forest onto the shale barren, we began to look around for the white-haired leatherflower, and I soon spotted a large clump growing on a nearby rock.  We were disappointed to find it had already flowered, but its elegant spiraled seeds made up for it.

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White-haired Leatherflower (Clematis albicoma)

As we were photographing the white-haired leatherflower, I noticed several clumps of Kate’s mountain clover growing on the rock above it.  Kate’s mountain clover (Trifolium virginicum) is endemic to rock outcrops in the Mid-Atlantic states, but unlike many other shale-barren plants, it can grow on types of rock other than shale.  For instance, at a site in Loudoun County that I wrote about earlier this year, it grows on a diabase outcropping.

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Kate’s Mountain Clover (Trifolium virginicum)

We continued to carefully pick our way through the barren, pausing here and there to examine plants.  Large mats of shale-barren pussytoes (Antennaria virginica) grew everywhere — sometimes we had to work hard to avoid stepping on them.  Clumps of shale-barren wild buckwheat (Eriogonum allenii) were also abundant; their large, leathery leaves stood out against the wiry leaves of the pussytoes.  The brilliant purple and yellow flowers of downy wood mint and Maryland hawkweed added the occasional splash of color to the scene.  I examined one of the large rocks closely, finding maidenhair spleenwort and moss phlox mixed in with the blunt-lobed woodsia and thick mats of rock spikemoss.

All too soon it was time to go, as we had one more important stop planned.  As we drove back down the road, we kept our eyes out for the mystery phlox we’d seen on the way in.  Suddenly a flash of bright pink appeared on the road bank.  We scrambled out to take a look.  This plant had brilliant pink, five-petaled flowers and super narrow, lance-shaped leaves.  A quick look at the key in the Flora of Virginia confirmed our suspicions: this was the state rare sword-leaved phlox (Phlox buckleyi), an endemic of shale woodlands.

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Sword-leaved Phlox (Phlox buckleyi)

Our final stop of the day was another road bank, also in Bath County.  This stop was the site for Millboro leatherflower, one of the rarest plants we could see that day.  We hoped it would sill be blooming, as its seeds are not nearly as beautiful as white-haired leatherflower, in my opinion.  We turned onto the road and began slowly driving up it, scanning the shaley banks on either side for leatherflowers.  We were getting close to the end of the road when Drew spotted the first one.  We leapt out of the car and ran over to check it out.  It was still blooming, its drooping, purple, tube-shaped flowers in pristine condition.  Soon we found several more nearby.

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Millboro leatherflower (Clematis viticaulis)

The Millboro leatherflowers were growing right out of the shale flakes with common wild quinine and New Jersey tea.  The leatherflowers were so close to the roadside that it looked like one bad land slide was all that it would take to destroy the population.  I wondered how many other sites for this rare and beautiful flower there could be given its very specific habitat requirements and its tiny, three county range.  They seemed to be thriving on that road bank despite conditions too harsh for many other plants.  Hopefully they will continue to do well…

 

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