Spiranthes arcisepala M.C. Pace, 2017

Pace, Matthew C. & Cameron, Kenneth M., 2017, The Systematics of the Spiranthes cernua Species Complex (Orchidaceae): Untangling the Gordian Knot, Systematic Botany (Basel, Switzerland) 42 (4), pp. 1-30 : 11-16

Spiranthes arcisepala M.C. Pace , sp. nov. —TYPE: U. S. A. New York: Hamilton County, just east of Long Lake, town of Long Lake , north of Shaw Pond in wet roadside ditch and Sphagnum seep under a power-line cut along Newcomb Road / 28N, collected 4 September 2014, Pace 636 (holotype: NY; isotypes: AMES, BH, CM, K, US, RENZ, WIS).

Spiranthes arcisepala is most similar to S. cernua s. s. and S. ochroleuca . It can be distinguished from S. cernua s. s. by its more open spiraled inflorescence, smaller flowers, and rounded labellum apex. It can be distinguished from S. ochroleuca by its white colored labellum, and can be distinguished from both S. cernua s. s. and S. ochroleuca by its downward arching lateral sepals.

Terrestrial, acaulescent, deciduous herb, to ca. 46 cm tall. Roots fasciculate, fleshy, slender. Leaves 1–4, basal, held upright, remaining until after anthesis, withering shortly thereafter, linear-lanceolate to slightly lanceolate, bluntly acuminate, leaf base tapered and decurrent. Peduncle glabrous, 1–2 small leafy cauline bracts occasionally present (frequently absent), quickly reducing to adpressed, clasping, lanceolate, acute bracts; spike a single row of flowers in an open to slightly tightly coiled spiral (typically appearing as 1 distinct ‘rank’), moderately to densely pubescent with blunt-tipped septate trichomes 0.5 mm long. Floral bracts densely pubescent, narrowly lanceolate, acuminate, concave around the ovary, to 12.3 mm long. Flowers resupinate, campanulate, slightly to moderately nodding and becoming more open with age, white, faintly to moderately fragrant with a general floral scent. Sepals free, moderately to densely pubescent with blunt-tipped capitate septate trichomes. Dorsal sepal slightly convex, slightly recurved to moderately upwardly reclined distally, lanceolate, bluntly acuminate, 8.3–10.6 mm long, 2–2.9 mm wide when flattened. Lateral sepals lanceolate, acute, slightly to strongly downwardly falcate from about 1/3 to 1/2 of their length, the tips often surpassing the lower labellum margin in profile, 8.3–9.7 mm long, 1.4–2.4 mm wide. Dorsal petals slightly concave, lanceolate, bluntly acute, slightly to strongly recurved at tips, with the dorsal sepal appearing stellate, 8.3–10.7 mm long, 2.1–2.5 mm wide when flattened. Labellum shortly clawed, free but clasping the column, keeled/concave for its length, recurved strongly downward at about 1/2 the distance from the claw to labellum apex, constricted near the recurvature and then dilating below, centrally glabrous and thickened, margin entire to very slightly undulating from the base until the area of recurvature, below point of recurvature margin becoming ruffled, margin white, central area of labellum white to extremely pale yellow back in the throat, 7.2–10.1 mm long, 4.4–5 mm wide below the callosities, 3.2–3.8 mm wide at the area of recurvature when flattened, 4.1–5.2 mm wide at widest point below recurvature; 2 basal callosities/nectar glands, white to pale yellow, conical, upright, 0.9–1.2 mm tall, with long, dense papillae at the base. Column protandrous, slightly rhombic, green, 3.6–5 mm long, with a fringe of minute glands or papillae in a thin crescent just below the stigmatic surface and with a pair of upright flaps or wings at each side and clasping the column, the wings green basally; column foot glabrous; rostellum well-developed, white to ivory, tapering to thin acute membranes at the apex; stigmatic surface glabrous, shiny; anther triangular-ovoid; pollinium attached to a well-developed viscidium; viscidium linear, immersed in the rostellum, leaving behind a narrow V-shaped rostellar remnant after removal, 1.6–1.8 mm long. Ovary moderately to densely pubescent with septate trichomes, green. Fruit a light brown upright ovoid capsule. 2 n 5 45. Figures 10 and 11 .

Etymology —Latin, ‘ arcisepala’ is a combination of ‘arcus’ (arching) and ‘sepalorum’ (sepals), referring to the downwardly arching lateral sepals of this species, serving as a relatively constant diagnostic morphological character. “Appalachian ladies’ tresses” is a suggested common name, indicating the main distribution of this species.

Spiranthes arcisepala ( Figs. 10 , 11 ) is a newly described and long overlooked cryptic sister species to S. ochroleuca 1 S. casei . It is primarily restricted to the mid- and northern Blue Ridge and Northern Highlands, Ridge and Valley, Great Valley, Appalachian Plateau, and Adirondack systems of the Appalachian Highlands in Nova Scotia, east-southeast Ontario, Quebec, Connecticut, Maine, Massachusetts, New Hampshire, New Jersey, New York, Pennsylvania, Virginia, Vermont, and West Virginia, and the eastern Interior Lowlands of northern Ohio, northeastern Indiana, and southern Michigan ( Fig. 14 ). The distribution of S. arcisepala is essentially similar to S. ochroleuca apart from the occurrence of the latter species further westward into the Great Lakes Basin and southward along the spine of the Appalachian Mountains to Kentucky, North Carolina, and Tennessee. Spiranthes arcisepala corresponds to one of the New England races of Sheviak (1982) and to the “fen ecotype” and “old field ecotype” of Homoya (1993). One of the key features distinguishing S. arcisepala is its downwardly falcate lateral sepals. This feature is relatively constant across populations, however occasional individuals and populations have lateral sepals that are just barely falcate (e.g. Fig. 11B, C ). In these instances, the flowers are still smaller than S. cernua s. s., S. incurva , and S. ochroleuca , and are essentially wholly white. Spiranthes arcisepala is typically found in wet, short-statured graminoid-cyperoid habitats including fens, bogs, mossy (often Sphagnum ) and lichen-covered seeps, and wet roadsides ( Fig. 15 ), and can occasionally be found growing interspersed with S. incurva . The flowers of S. arcisepala possess a faint general floral fragrance, perceivably similar to S. cernua s. s.

Figures

FIG.10. Spiranthes arcisepala. A. Habit. B.Inflorescence.C. Flower and floral bract in profile.D–G.Flower, dissected view.D. Dorsal sepal.E.Dorsal petal. F. Lateral sepal. G. Labellum. H. Labellum, column, and ovary in natural position. I–K. Column. I. Dorsal and ventral views. J. Profile.K.Anther. L. Pollinia. Drawn from Pace 1005 and Pace 1008 by Bobbi Angell.

FIG.11. Spiranthes arcisepala.A.Type location, Long Lake, Hamilton Co., New York. B.Delaware Co., New York, sample NY1.C.Indian Lake, Hamilton Co., New York. D. Wells, Hamilton Co., New York. E. Morris Co., New Jersey. F. Fayette Co., Pennsylvania.

FIG.14. Distribution maps of the S. cernua species complex s. s., based on herbarium specimens and phylogenetic sampling.A.S. arcisepala, S. cernua s. s., S. incurva, S. 3kapnosperia, S. niklasii. B. S. casei and S. ochroleuca. Maps produced by Elizabeth Kiernan, New York Botanical Garden GIS Lab.

FIG. 15. A–B. Habitat of S. cernua s. s. A. Marshy pond edge, with Nyssa sylvatica Marshall, Chamaecyparis thyoides (L.) Britton, Sterns & Poggenb., Sarracenia L., and Eriocaulon L., Lexington Co., South Carolina. B. Seeping, graminoid-cyperoid and brushy roadside, mixed with S. 3kapnosperia (type location), Transylvania Co., North Carolina. C–E.Habitat of S. incurva. C. Xeric roadside slope, with Solidago nemoralis Aiton and Andropogon gerardi Vitman, Orleans Co., Vermont; sample location of soch10. D. High diversity fen, Clark Co., Ohio, sample location of sc32a. E. Sandy, xeric dune swales and back dunes, co-occurring with S. magnicamporum (with Mr. S. Martella), Lake Co., Illinois. F. Habitat of S. niklasii; xeric, prairie-like opening, Greene Co., Arkansas, sample location of AR1. G–H. Habitat of S. arcisepala. G. Seeping fen, McKean Co., Pennsylvania. H. Type location; roadside ditch and Sphagnum seep with Eriophorum virginicum L. under a power-line cut, Hamilton Co., New York.