Spiranthes arcisepala was first described by Matthew Pace and Kenneth Cameron in 2017.  Its small white flowers appear wider and more “bell-shaped” than other members of the S. cernua complex, with a labellum that appears rounded at the tip and lateral sepals that often curve downward and are very distinct from the upper petal.  Some populations, however, do exhibit lateral sepals that curve up, which can make clear field identification challenging.  Flowering time for this species is mid to late-September, although some populations will persist into October.

S. arcisepala can grow up to 20 inches tall but plants are usually only about half that size. Like other members of the S. cernua complex, its narrow leaves usually wither and disappear by the time it blooms. It is found in fens, bogs, wet roadsides and fields, and along pond margins.

This species has a relatively limited range in the Appalachian region from Nova Scotia to West Virginia, but some populations are found in far northern Ohio and into southern Michigan.  It is probably the most common Spiranthes species in Pennsylvania except in the far southeast where it gives way to S. cernua s.s. 

Sources:

Pace, M.C. and K.M. Cameron. 2017. The systematics of the Spiranthes cernua species complex (Orchidaceae): Untangling the Gordian Knot. Systematic Botany, 42(4):1–30.

Hough, Michael and Matthew Young. 2021.  A Systematic Survey of the Spiranthes cernua Species Complex (Orchidaceae) in New York.  The Native Orchid Conference Journal, 18.3: 22-56.