The generic name is derived from the Greek koilos glossum meaning "hollow tongue," referring to the hollow spur on the tongue-like labellum.
Plant arises from fleshy, forked roots and ranges in height from 10-55 cm. Leaves of the Frog Orchid are 5-14 cm long and 2-7 cm wide; leaves at the base of the orchid are obovate to elliptical, while leaves higher on the stem become lanceolate. Two to six leaves are found one one plant, and leafing is alternate.
Inflorescence of the orchid is a dense spike-like cluster containing 7 to 70 small flowers. Flowers are greenish in color, and often tinged with purple, reddish, or red-brown color. Flowers are subtended by conspicuous long, tapering bracts which are 1-6 cm long, with the lower bracts longer and typically greatly exceeding the length of the flower. Sepals are oval with little or no point, 3-7 mm long and 2-4 mm wide and dark green. Sepals join with petals to form a hood opposite the lower petal of the flower. Petals are long and narrow, 3.5-5 mm long and about 0.5 mm wide, and curve inwards. The lower petal is strap-shaped and usually split at the very tip to form two or three tooth-like divisions, with the middle tooth smaller than the others. It is 5-11 mm long and 1-4 mm wide. A 2-3 mm long nectar spur projects behind the labellum.
The Frog Orchid flowers in late May and early June. It is either pollinated by bees and small wasps, or reproduces autogamously by incoherent pollenia.
The Frog Orchid can be mistaken for the Pale Green Orchid, but can be best distinguished by the labellum, which is notched at the apex and does not have the tubercle of the Pale Green Orchid.