Spiranthes cernua (L.) L. C. Rich.

Nodding ladies'-tresses

The specific epithet cernua is the Latin meaning "nodding," referring to the nodding flowers of this species.

DESCRIPTION: Plant pubescent above the leaves, 10-40 cm tall (including inflorescence), arising from a cluster of fleshy, slender roots. Leaves 2-3(-5) mostly basal, oblanceolate to linear-lanceolate, 10-20 cm long and 0.5-1 cm wide, grading into reduced sheathing bracts below the inflorescence. Inflorescence a downy, spicate raceme of 20-40 white flowers, 10-40 cm tall, dense and multi-ranked, each flower subtended by an elongate, ovate-lanceolate bract. Sepals linear-lanceolate, 6-10 mm long and about 2 mm wide, the lateral sepals with margins inrolled, and typically spreading slightly and ascending, dorsal sepal connivent with petals to form a hood over the column, sepals white to creamy-white. Petals linear-lanceolate to linear, 6-10 mm long and 1-2 mm wide, closely appressed to the dorsal sepal, tips of dorsal sepal and petals reflexed slightly, colored as sepals. Labellum obovate to ovate, 6.5-11 mm long and 3-6 mm wide, white to creamy-white colored with the central portion sometimes thickened and slightly yellowish, the apex bent downwards and the central portion somewhat constricted, the base of the labellum with two prominent, incurved, pubescent calli.

Easily confused with other species of Spiranthes, particularly S. casei and S. magnicamporum. The spreading lateral sepals, leafless stem at flowering and odor of S. magnicamporum separate it from most S. cernua, which has appressed lateral sepals, a leafy stem at anthesis and usually scentless flowers. However, there are some races of S. cernua which approach many of these aspects of S. magnicamporum. Separating these specimens is extremely difficult, with the best character being embryony: the seeds of S. magnicamporum are monoembryonic, whereas a large percentage of the seeds of S. cernua are polyembryonic. Separating S. cernua from S. casei is also difficult. The closely appressed lateral sepals of S. casei and its creamy color differ from the more spreading sepals and white color of S. cernua. In overall appearance, the flowers of S. cernua appear larger and more open than those of S. casei Finally, the inflorescence of S. casei is nearly always loosely single-ranked, whereas the inflorescence of S. cernua is usually multi-ranked and frequently densely so.

The problems in identifying specimens of Spiranthes are centered around S. cernua, and are not the result of too much splitting in this group. The taxa that have been recently separated from S. cernua (S. casei, S. magnicamporum, and S. ochroleuca) are all distinct and invariable. both in morphology and in chromosome number. S. cernua, on the other hand, is extremely variable in morphology and chromosome number. Numerous polyploid and aneuploid races of S. cernua exist, and often appear radically different from "typical" S. cernua. Charles Sheviak (1982) has published a thorough and detailed examination of the S. cernua problem; anyone serious about Spiranthes taxonomy should consult this work.

Commonly found in moist, sandy, acidic or basic soils. Typical habitats in Wisconsin are moist meadows, lakeshores, and roadside ditches. Spiranthes cernua is an early successional species, and is usually found in areas that have been disturbed. Mowing, if done at the right time, simulates disturbance by removing competing vegetation. S. cernua will often persist for many years in mowed areas, such as roadside ditches.

August 10-September 20.

Luer (1975) and Catling (1983b) have both caught bumblebees pollinating Spiranthes cernua.

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