This plant keys well to D. appalachiense and the habitat (canopy gap in a shale woodland) fits for that taxon. I am not convinced that D. appalachiense isn't a hybrid (boscii x linearifolium), but that entity is currently G1 and state historic for PA. But until more evidence is provided, this must be treated as species of conservation significance.
The attached photos provide some support for the morphological intermediacy of this individual with D. boscii and D. linearfolium. Both potential parent species were within 3m of the hybrid; boscii was approx. 1.5m uphill and may be the mother plant.
Images 1-3: Details and habit of just D. appalachiense.
Images 4&5: D. appalachiense (left) and D. boscii (right).
Images 6-9: D. boscii (left), D. appalachiense (middle), and D. linearifolium (right). Three spikelets from each taxon are shown.
Note the intermediate leaf shape and spikelet size of D. appalachiense compared with its putative parents. The longer culms and bearding of the nodes could be traits from boscii. The exertion and width of the vernal inflorescences, as well as the long spreading hairs present on the upper sheaths, could be traits from linearifolium.
Observations of the putative parents:
D. boscii: https://www.inaturalist.org/observations/176857848
D. linearifolium: https://www.inaturalist.org/observations/176827234
Opening in swamp woods, low ground, wet soil. Sprawling growth with erect flower stems, growth was more upright where other plants provided support.
ELC1095 Spécimen récolté, déposé à l'herbier MT (Montréal). Avec @elbourret. Achene at the top lupuliformis, at the bottom nearby Carex lupulina.
Marécage à Liquidambar et Acer rubrum en bordure d'un cours d'eau à flot lent à peine endigué par les castors (digue haute de moins de 30 cm). Sol limoneux. Avec Carex gigantea dans les zones plus humides, Carex lupulina, Carex louisianica, Panicum et Carex tribuloides. Zone ombragée. Pente: nulle, Exposition: Na, Drainage: mauvais. 15 plants répertoriés. Peu fréquent.
Roadside. Obviously colonial in nature. Lower leaves gone. Flowers 2cm in diameter. Some pics taken outdoors, some indoors, hence the color difference.
Maybe?
This roadside area with a small creek running through it was logged early this year. Lots of this plant is growing, along with Penstemon, Coreopsis major, Pycnanthemum tenuifolium, along with the usual Rubus, Erichtites, and Eupatorium capillifolium. Plenty of Rudbeckia laciniata in a moist soil area.
Hybrid? Pink variant? Leaves very lanceolate. Lots of Asclepias lanceolata around.