Spiranthes arcisepala M.C. Pace - Appalachian Ladies' Tresses


 

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Spiranthes arcisepala - (image 1 of 6)

 

Taxonomy

Family: Orchidaceae

Habitat

Fens, bogs, seeps, wet roadsides, occasionally in somewhat drier habitats.

Associates

 

 Distribution

Nova Scotia, east-southeast Ontario and Quebec, south through ME, NH, VT, MA, CT, NY, NJ, PA, northern OH, southern MI, and extreme northeast IN, south from PA through the mid- and northern Blue Ridge and Northern Highlands.

Morphology

Perennial to 46 cm. Leaves remaining until anthesis and withering shortly after; flowers 5 mm or longer, campanulate, slightly to moderately nodding and becoming more open with age, white; lateral sepals flattened, lanceolate, acute, slightly to strongly downwardly falcate, the tips often surpassing the lower labellum margin in profile; labellum abaxially white or very pale yellow, centrally glabrous and white to very pale yellow back in the throat, margin crisped and lacerate below the point of curvature.

Notes

Flowers late August to September

Wetland indicator: NA

Not described until 2017, this species is part of the Spiranthes cernua complex. It is a cryptic sister species to S. ochroleuca and S. casei. Perhaps best distinguished for the white and relatively short lip and downwardly falcate lateral sepals.

Update March 2020:

Recent genetic testing has found that several plants that were originally determined to be S. incurva are actually this species, suggesting that it is even more cryptic in nature than originally thought. This also suggests that the shape of the lateral sepals is not a completely reliable trait and the presence of a relatively short lip that is rounded at the apex should be given greater weight in identification. Many of the morphologically ambiguous plants were found within populations of typical S. arcisepala, though a few were not.

Example of plant (left) with straight lateral sepals that was genetically determined to be S. arcisepala.

More work needs to be done to determine if hybridization could play a role in this variation.

References

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

 


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 Michael Hough 2017