Listera convallarioides (Sw.) Nutt.

Broad-leaved twayblade

The specific epithet convallarioides is from the Latin meaning "Convallaria-like," apparently because Swartz felt that the leaves of Listera convallarioides resembled those of the genus Convallaria (the Lily-of-the-Valley.

DESCRIPTION: Plant glabrous below inflorescence, 12-25 cm tall, arising from an cluster of slender, fibrous roots. Leaves two, opposite, located near the middle of the stem, ovate-elliptical to nearly orbicular, 3-6 cm long and 2.5-5 cm wide. Midrib +/- prominent, forming a slight keel below. Inflorescence a lax terminal raceme of translucent green flowers, 7-20 flowered; each flower subtended by a minute lanceolate bract. Scape of inflorescence finely pubescent. Dorsal sepal elliptical to lanceolate, reflexed, 4-5 mm long and 1-2 mm wide, green; lateral sepals lanceolate to linear-lanceolate, distinctly falcate and reflexed, 4.5-5.5 mm long and about 1-1.5 mm wide, green. Petals linear and only slightly falcate, 4-5 mm long and about 1 mm wide, colored as the sepals; typically reflexed back along the ovary. Labellum cuneate; 7-11 mm long and 3-5 mm wide, the apex rounded and slightly lobed, typically with a minute tooth between the lobes, the base of the lip attenuated into a thin stalk (or claw) with a pair of small projections at the point of constriction; colored as sepals and petals, central portion typically thickened and darker green.

Listera convallarioides is most likely to be confused with other species of Listera, but can be easily distinguished by its cuneate, undivided labellum. The two other species of Listera found in Wisconsin, L. auriculata and L. cordata, both have labella that are deeply divided, whereas the labellum of L. convallarioides is barely notched at its apex.

Listera convallarioides is usually found in moist northern mixed deciduous/coniferous forests, where it frequently is found growing in moist to mucky humus in shallow depressions. In such situations it may form extensive colonies.

Early July-early August.

Unknown in the published literature. However, given that Listera cordata is pollinated by fungus gnats, and my observation of a similar insect pollinating L. auriculata, it seems likely that L. convallarioides is also pollinated by fungus gnats.

DISCUSSION: This species hybridizes with Listera auriculata to form the hybrid L. X veltmanii Case (Case 1964), which has been collected in Bayfield County. The hybrid is generally intermediate between the two parents, particularly in the shape of the labellum. Catling (1976) has written detailed description of this hybrid and its distribution.

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