Spiranthes niklasii 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 : 21-22

Spiranthes niklasii M.C. Pace. sp. nov. [probable ancient Spiranthes cernua 3 Spiranthes ovalis ]—TYPE: U. S. A. Arkansas: Yell Co., Ouachita National Forest, near Forest Road 86, along Fourmile Creek (mostly dry), in cobbled soil, within a Liquidambar -Carpinus -Ostrya -Acer forest, south of the western end of Linn Barker Mountain and the eastern end of Fourmile Mountain, collected 5 October 2016, Pace 1036 (Holotype: NY; isotypes: ANHC, BH, US).

Spiranthes niklasii is most similar to S. cernua s. s. from which it can be distinguished by a central ridge of small papillae on the adaxial surface of the labellum, more strongly campanulate flowers, and usual preference for a more xeric habitat. It can be distinguished from S. ovalis by its centrally papillate labellum, flattened lateral sepals (vs. cupped), and upright callosities (vs. strongly incurled). It can be distinguished from both species by its typically fugacious leaves at anthesis.

Terrestrial, acaulescent, deciduous herb, to ca. 41 cm tall. Roots fasciculate, fleshy. Leaves 1–2, basal, held upright, fugacious at anthesis (rarely remaining until anthesis and withering shortly thereafter), linear-lanceolate to lanceolate, acuminate, leaf base tapered and decurrent. Peduncle with adpressed, clasping, lanceolate, acute bracts; spike a single row of flowers in a moderately to tightly coiled spiral (appearing as 1–4 “ranks”), moderately to densely pubescent with blunt-tipped septate trichomes to 0.5 mm long. Floral bracts moderately to densely pubescent, lanceolate, acuminate, concave around the ovary, 10–12.5 mm long. Flowers campanulate, held perpendicular to the inflorescence to moderately nodding, white to pale ivory. Sepals free, moderately to densely pubescent with blunt-tipped capitate septate trichomes. Dorsal sepal slightly convex, slightly to strongly recurved near the tip, lanceolate, bluntly acuminate, 8.3–8.6 mm long, 1.8–2.8 mm wide when flattened. Lateral sepals lanceolate, acute, straight to just barely upwardly falcate, angled slightly upward, the tips often meeting the dorsal sepal and petals, 7–9.4 mm long, 1.3–1.8 mm wide. Dorsal petals slightly concave, lanceolate, bluntly acute, slightly to strongly recurved at tips, with the dorsal sepal appearing stellate, 7.7–9.2 mm long, 8.3–8.6 mm wide when flattened. Labellum minutely clawed, free but clasping the column, keeled/concave for its length, recurved strongly downward at about 1/3 to 1/2 the distance from the claw to labellum apex, with a central ridge or patch of small papillae along the midvein, margin entire to very slightly undulating from the base until the area of recurvature, below point of recurvature margin becoming shallowly laciniate and crisped, margin white, central area of labellum white to very pale yellow, 7.3–9.2 mm long, 3.3–4.8 mm wide below the callosities, 2.2–2.6 mm wide at the area of recurvature when flattened, 1.4–3.7 mm wide below the recurvature, lanceolate to oblong, apex acuminate to rounded; 2 basal callosities/nectar glands, white to yellow, prominent, upright, 0.6–1.1 mm tall, with long dense papillae at the base. Column protandrous, slightly rhombic, green, 2.5–3.6 mm long, with a fringe of minute glands or papillate below the stigmatic surface, with a pair of prominent, upright flaps or wings at each side and clasping the column, the wings green basally, becoming white to translucent, column foot glabrous; rostellum well-developed, white to ivory, becoming dark drown with age, tapering to thin acute membranes at the apex, 1.2–1.5 mm long; stigmatic surface glabrous, shiny; anther pale-brown, triangular-ovoid; pollinium attached to a well-developed viscidium, yellow; viscidium linear, slightly sticky, immersed in the rostellum, leaving behind a narrow V-shaped rostellar remnant after removal, 1–1.3 mm long. Ovary moderately to densely pubescent with septate trichomes. Fruit a light brown ovoid capsule. Figures 3 and 17 .

Etymology —The specific epithet “ niklasii ” honors Karl J. Niklas, Ph.D. (b. 1948), for his many contributions to botany, paleobotany, and evolutionary biology. Throughout his 43 yr of elegant scholarship, leadership within the botanical community (e.g. President, Botanical Society of America, 2008–2009), and dedicated teaching as a professor of Plant Biology at Cornell University, Niklas has mentored and inspired a generation of botanists, including M. Pace. A suggested common name for S. niklasii is “Niklas’ ladies’ tresses”.

The discovery of S. niklasii ( Figs. 3 , 17 ), likely ancient S. cernua s. s. 3 S. ovalis , is perhaps one of the more unexpected results of our research. Although previous phylogenetic research found that S. ovalis was a member of the S. cernua species complex s. l. ( Dueck et al. 2014; Pace and Cameron 2016), these two species had never previously been hypothesized to hybridize. Herbarium specimens of S. niklasii were originally identified as tentative S. cernua s. l., however, close observation found papillae along the central vein of the labellum, a character not present in S. cernua s. s. (or S. ovalis ). This unusual character prompted M. Pace to conduct fieldwork in Arkansas, with an emphasis on the Ouachita Mountains. When samples of these plants were included in our molecular analyses, they displayed strong discordance between nuclear and chloroplast datasets, with the chloroplast datasets hypothesizing a close relationship to S. ovalis ( Figs. 5 , 7 ).

The labellum shape of S. niklasii is somewhat variable, however, overall flower shape is distinctly and strongly campanulate, and the plant is often leafless at flowering; these characters are not typically found in either parental species. Similarly, although S. niklasii is often found along streams, these streams are typically dry at anthesis, and many populations grow in xeric graminoid prairie-like clearings and edges within dry Pinus -Quercus -Acer - Liquidambar -Carpinus - Ostrya forests ( Fig. 15 ), a habitat somewhat intermediate between the open wet graminoid-cyperoid habitats of S. cernua s. s. and the dolomitic oak-savannah to closed-canopy forested habitats of S. ovalis .

Spiranthes niklasii is primarily restricted to the Ouachita Mountains of Arkansas and eastern Oklahoma, with small disjunct populations in the south-central Boston Mountains and on Crowley’ s Ridge in northeastern Arkansas ( Fig. 14 ). Although S. cernua s. s. and S. ovalis are both found over much of southern North America and potentially share pollinators ( Catling 1980), is it unclear why the hybrid species S. niklasii displays a restricted and geographically specific distribution. The Ouachita Mountains contain 20 known endemic plant species and are the second most species-rich area within the wider region following southeastern Texas, with ca. 1,500 known plant species ( Kartesz 2015); this mountain system is also a known region of species diversity and endemism for North American Plethodontid salamanders ( Shepard et al. 2011; Steffen et al. 2014). The Ouachita Mountains are unusual in that they are one of just a few east-west oriented mountain ranges in North America north of Mexico, and they have been hypothesized to have served as glacial refuges during Ice Ages. Additional research is needed to understand how the unusual geologic history of the region might have affected the evolution of its flora and fauna, including the nearly endemic orchid S. niklasii .

Figures

FIG. 3. A. Spiranthes casei, Michigan; photo: Aaron Strouse, used with permission. B–C. Spiranthes ochroleuca, Rutland Co., Vermont. C. Characteristic ochroleucous-yellow coloration on abaxial labellum surface. D. Spiranthes ovalis var. erostellata Catling, Waukesha Co., Wisconsin, sample so2. E. Spiranthes niklasii, Yell Co., Arkansas (type location). F. Spiranthes 3kapnosperia, Transylvania Co., North Carolina (type location).

FIG.17. Spiranthes niklasii. 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,with detail of central adaxial papillae. H.Labellum, column,and ovary in natural position, with detail of abaxial labellum surface. I–K. Column. I. Dorsal and ventral views. J. Profile. K. Anther and pollinia. Drawn from Pace 1036 by Bobbi Angell.

FIG. 5. Bayesian phylogenetic tree reconstructions. Posterior probabilities within species clades are only indicated if they are. 0.90. The discordant positions of the three hybrid taxa are highlighted; colors the same as in Fig. 7. A. Bayesian phylogenetic tree reconstruction based on the combined five-locus chloroplast data. B. Bayesian phylogenetic tree reconstruction based on the combined ACO 1 ITS nuclear data.

FIG. 7. Phylogenetic network from NeighborNet analysis of the S. cernua species complex s. l. plus S. odorata, using the nuclear 1 chloroplast dataset, including all samples of both hybrid and non-hybrid taxa. The position of species is indicated by colored ovals.

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.

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.