Listera cordata (L.) R. Brown

Heart-leaved twayblade, heartleaf twayblade

The specific epithet cordata is a Latin term referring to the heart, in reference to the heart-shaped leaves of the plant.

DESCRIPTION: Plant glabrous below inflorescence, 8-25 cm tall, arising from an cluster of slender, fibrous roots. Leaves two, opposite, located near the middle of the stem, cordate to somewhat deltoid, 1-4 cm long and 1-3.5 cm wide (at their widest point). Inflorescence a dense to lax terminal raceme of yellowish-green to madder-purple flowers, 5-20 flowered; each flower subtended by a minute lanceolate bract. Scape of inflorescence finely pubescent. Sepals ovate to elliptical, 1.5-3 mm long and about 1 mm wide, yellowish-green to madder-purple. Petals similar to sepals. Labellum linear-oblong; 3-5 mm long and about 1 mm wide, the apex deeply divided to about 1/2 its length, the base with two horn-like projections.

Listera cordata is most likely to be confused with other species of Listera, but can be easily distinguished by its deeply divided labellum. The two other species of Listera found in Wisconsin, L. auriculata and L. convallarioides, both have labella that are less deeply divided than the labellum of L. cordata. In addition, the labella of both of these taxa are wider than those of L. cordata.

Listera cordata is typically found growing in dense hummocks of Sphagnum in boggy areas. Usually it is found in canopied bogs (such as Thuja and Picea bogs), but L. cordata can also be found in Sphagnum hummocks in moist forested areas.

May 25-July 5.

Ackerman and Mesler (1979) observed fungus gnats pollinating Listera cordata in California. I have observed fungus gnats pollinating L. cordata in Door County. Unlike many sapromyophilous plants (those pollinated by fungus gnats and related dipterans), the flowers do not apparently mimic a typical larval or adult food source (decaying fungi); rather, the gnats appear to visit the flowers only to feed on the minute amounts of nectar produced.

DISCUSSION: Along with the two species of Malaxis, Listera cordata is one of the smallest-flowered orchids in Wisconsin. The plants are best appreciated with a magnifying lens, and can be quite beautiful when seen up close. The flowers typically remain fresh for a long period of time, even after the flowers are pollinated. While Fuller (1933) considered L. cordata rare and local, it is more likely that it is under-collected. The small size of the plants and their inconspicuous coloration make them difficult to find, even when one is actively searching for them. Diligent searching in suitable habitat in the northern counties would most likely result in the discovery of more locations for this species.

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