Specimens supporting the plausible report of the more southern, spring blooming Spiranthes vernalis from Kalamazoo Co. (McKenna, 2004) could not be located, though the occurrebce of this species in SW Michigan is plausible.
1. Leaves widely spreading or essentially lying flat in a basal rosette, short–petioled, sometimes withered or wilted at flowering time, their blades less than 4.5 (rarely 5.5) cm long, about 2/5 as broad as long or broader; perianth 2.5–5.5 mm long.
2. Flowers with a deep green center to the lip; tuberous roots several.
2. Flowers with pure white lip; tuberous root solitary.
1. Leaves ascending, sheathing basally and not distinctly petioled, usually present at flowering time (except in S. magnicamporum, with flowers 9–11 mm long), their blades (non-sheathing portion) over 4.5 cm long and less than 2/5 as broad as long; flowers usually in 2 or more rows in a ± crowded spike (sometimes one-sided); perianth larger than 5.5 mm long (except in the late September- and October-blooming S. ovalis).
3. Largest leaves (non-sheathing portion) about 5–10 times as long as wide, lanceolate to oblanceolate; lip bright yellow or yellowish orange; leaves all basal (rarely 1 cauline), 4.5–10 cm long, the stem bearing 1–2 cauline bracts (including reduced leaf, if present); flowering in June and early July.
3. Largest leaves commonly over 10 times as long as wide, or leaves absent; lip white or creamy, sometimes the central portion pale yellow; leaves often present on lower portion of stem, the cauline bracts and leaves totaling 3–6; flowering in mid- to late summer and fall.
4. Lower flowers with perianth 3–7.5 (–8) mm long (most easily measured using the dorsal sepal); flowers in one row, usually in a loose spiral because of the twisted rachis, or more tightly spiraled if the perianth is only 3–4 mm long.
5. Perianth 5.5–7.5 (–8) mm long; rachis and bracts conspicuously capitate-glandular.
5. Perianth ca. 3–5 mm long; rachis sparsely glandular, bracts glandular only on the margins and base.
4. Lower flowers with perianth 7–11 mm long (most easily measured using the dorsal sepal); flowers in 2 or more rows, often tightly spiraled.
6. Lip fiddle-shaped, strongly constricted behind expanded apex; lateral sepals united for at least half their length with dorsal sepal and lateral petals, forming a hood.
6. Lip ± oblong, often rather erose-margined but not strongly constricted; at least the lateral sepals free (or easily separated if connivent when young).
7. Plant leafless when flowering; upper cauline bracts usually overlapping; basal calli on either side of lip short, about as wide as long; lateral sepals in the fresh flowers curved and spreading.
7. Plant with leaves usually present at flowering time, upper cauline bracts not or barely overlapping; basal calli on either side of lip longer than wide; lateral sepals in the fresh flowers appressed.
8. Perianth pure white, except sometimes the central portion of the lip creamy; larger flowers usually 8–11 mm long; lip at most slightly curved from claw; claw 0.3–0.8 mm long.
8. Perianth creamy or yellowish; larger flowers usually 7–9 mm long; lip strongly bent from the claw; claw 0.8–1.5 mm long.