Monday, May 3, 2021

[Botany • 2021] Spiranthes bightensis (Orchidaceae) • A New and Rare Cryptic Hybrid Species Endemic to the U. S. Mid-Atlantic Coast


Spiranthes bightensis M.C. Pace

in Pace, 2021. 
Atlantic Ladies Tresses || 

Recognizing species diversity is challenging in genera that display interspecific similarity and intraspecific variation; hybridization and the evolution of cryptic hybrid species amplifies these challenges. Recent molecular and morphological research focused on the systematics of Spiranthes (Orchidaceae) support hybrid speciation as an important driver of species diversity, particularly within the S. cernua species complex. Working under an integrated history-bound phylogenetic species concept, new molecular and morphometric data provide evidence for a new and rare cryptic hybrid species resulting from the ancient hybridization of S. cernua × S. odorata, here described as Spiranthes bightensis. Although S. bightensis is regionally sympatric with S. cernua it does not co-occur with that species, and it is allopatric with respect to S. odorata. Endemic to a narrow region extending from the Delmarva Peninsula to Long Island, New York, this new species occurs in the shadow of the Northeast megalopolis and appears to have undergone a major population decline over the last 200 years. By recognizing this distinct evolutionary lineage as a new species, this research is the first step towards developing conservation protocols for this rare species and highlights the importance of the North American Geologic Coastal Plain for biodiversity conservation and evolution.

Keywords: evolutionary phylogenetics, North American Geologic Coastal Plain, Northeast megalopolis, Spiranthes cernua, Spiranthes odorata, species complex, Monocots

Line drawing of Spiranthes bightensis M.C. Pace.
A. Habit and leaf detail. B. Inflorescence. C. Inflorescence detail. D. Floral bract and flower. E–M. Dissected flower. E. Dorsal sepal. F. Dorsal petal. G. Lateral sepal. H. Labellum, flattened. I. Labellum and column in natural position. J. Column, profile view. K. Column, ventral and dorsal view. L. Anther. M. Pollinia.
Drawn from Austin s.n. barcode 01392822 (NY) and Pace 608 (NY) by Bobbi Angell.

Spiranthes bightensis M.C. Pace, sp. nov. 
[ancient S. cernua × S. odorata].
—Type: U. S. A. Maryland: Worcester County, Bainbridge Park pond, Ocean Pines, off of Beaconhill Rd., ca. 3.5 km west of Isle of Wight Bay, 23 October 2013, 
Pace 608 (holotype: NY, isotypes: K, US).

Diagnosis. Spiranthes bightensis is most similar to S. cernua, from which it can be distinguished by its stoloniferous roots (vs. non-stoloniferous), typically longer and wider, more lanceolate leaves (vs. linear-lanceolate, 15–21.4 × 1.4–1.7 cm vs. 8.7–20 × 0.4–1.1 cm, Fig. 3, 4, Table 1) commonly fragrant flowers (vs. typically lacking fragrance), and slightly thickened central labellum (vs. centrally membranous). Spiranthes bightensis can be distinguished from S. odorata by its truncate column to rostellum transition zone, vs. lanceolate, and shorter and narrower leaves (15.0–21.4 × 1.4–1.7 cm vs. 13–51.7 × 1.8–2.7 cm).

Etymology:— From the Old English / Anglo-Saxon ‘byht’, meaning bend or bay, a bight is a shallowly curved coastline or extremely wide bay; its use here refers to the Mid-Atlantic and New York Bights, which stretches from the Nantucket Shoals off southern New England southward to Cape Lookout, North Carolina. Spiranthes bightensis is endemic to the central region of this bight. Atlantic Ladies Tresses is the suggested common name. 

Distribution map of Spiranthes bightensis, highlighting population loss over time.
A. Collections made pre-1890’s–present (the hypothesized original distribution of S. bightensis). B. 1900–present. C. 1950–present. D. 2000–present.
Prepared by Elizabeth Gjieli, NYBG GIS Lab.

Matthew C. Pace. 2021. Spiranthes bightensis (Orchidaceae), A New and Rare Cryptic Hybrid Species Endemic to the U. S. Mid-Atlantic Coast. Phytotaxa. 498(3); 159–176. DOI: 10.11646/phytotaxa.498.3.2