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.
SIMILAR SPECIES: 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.
HABITAT: 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.
FLOWERING DATES: May 25-July 5.
POLLINATION: 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.
WI DISTRIBUTION: 
U.S. DISTRIBUTION:
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