Oreojuncus trifidus (Linnaeus) Záveská Drábková & Kirschner. Highland Rush. Phen: Jun-Sep. Hab: Rock crevices at high elevations, on greenstone, mica schist, amphibolite, metabasalt, hornblende gneiss, and quartzitic sandstone. Dist: The species is circumboreal, occurring in arctic-alpine situations in n. Eurasia, ne. North America, Canadian arctic islands (Baffin, Nunavut), Greenland, Iceland. In North America, it ranges from n. NL (Newfoundland and Labrador) to n. QC, south to s. New England and NY; disjunct southwards in PA (1868 collection with vague locality), MD (Cumberland Narrows, Alleghany County), WV (North Fork Mountain, Pendleton County), VA (Stony Man, Page County), TN (Mount Leconte, Blount County), and NC (Craggy Pinnacle, Craggy Dome, and Craggy Gardens, Buncombe County; Eagle Cliff, Mitchell County; Three Top Mountain, Ashe County).

Origin/Endemic status: Native

Taxonomy Comments: As with many circumboreal species of polymorphic nature, there is disagreement over the recognition and rank of taxa. The "monanthos entity" (of limestone areas of c. Europe) is variously accorded species, subspecies, or variety status, or lumped into the "trifidus entity"; here it is accorded species status, following recent European researchers. Hämet-Ahti (1980) correctly showed that Southern and Central Appalachian O. trifidus (from acidic and mafic gneisses and schists and quartzitic sandstones) does not belong to O. monanthos (Jacquin) Záveská Drábková & Kirschner (Juncus monanthos, J. trifidus ssp. monanthos, J. trifidus var. monanthos), but her treatment of Appalachian plants as J. trifidus ssp. carolinianus Hämet-Ahti has been controversial. For now, this treatment follows Clemants (1990), who concluded that the primarily vegetative characters used to separate Appalachian plants from the European (blade lengths and relative positions) are too variable to warrant recognition of subspecies or varieties in the taxon. Further study is, however, warranted.

Synonymy: = K4, NeUS, NY, Zaveska Drábková & Kirschner (2013); = Juncus trifidus L. – NE, Kirschner (2002b), Kirschner (2002c); = n/a – Pa; < Juncus trifidus L. – FNA22, K3, S, Tn, Va; > Juncus trifidus L. ssp. carolinianus Hämet-Ahti – C, K1; >< Juncus trifidus L. var. monanthos (Jacq.) Bluff & Fingerh. – F, G, RAB, W, misapplied to our plants; > Juncus trifidus L. var. trifidus – F

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Wetland Indicator Status:

• Eastern Mountains and Piedmont: FACU (name change)
• Northcentral & Northeast: FACU (name change)

Heliophily: 8