Listera auriculata Wieg.

Auricled twayblade

The specific epithet auriculata is derived from the Latin auricula, which means "little ear," and refers to the ear-like projections (auricles!) at the base of the labellum.

DESCRIPTION: Plant glabrous below inflorescence, 10-20 cm tall, arising from an cluster of slender, fibrous roots. Leaves two, opposite, located near the middle of the stem, ovate-elliptical, 3-5.5 cm long and 2-4 cm wide. Midrib +/- prominent, forming a slight keel below. Inflorescence a lax to dense terminal raceme of green flowers, 7-16 flowered; each flower subtended by a minute lanceolate bract. Scape of inflorescence finely pubescent. Dorsal sepal obovate, 3.5-4 mm long and 1-2 mm wide, green; lateral sepals oblong to elliptical, distinctly falcate and reflexed, 4-4.5 mm long and about 1-1.5 mm wide, green. Petals linear and only slightly falcate, 3-3.5 mm long and about 0.7-0.8 mm wide, colored as the sepals; typically reflexed back along the ovary. Labellum oblong and narrowed in the middle; 7-11 mm long and 3-5 mm wide, the apex divided to form two teeth and the base forming two auricles which recurve back around the base of column; colored as sepals and petals.

Listera auriculata is most likely to be confused with other species of Listera, although it is most similar to L. convallarioides. L. auriculata can be separated from L. convallarioides by the shape of the labellum. The auricles at the base of the labellum of L. auriculata are large and reflexed, so that they wrap back around the ovary.

Listera auriculata is found almost exclusively in one habitat: on sandy soil under alders along small streams. The plants typically grow out of a carpet of moss.

June 20-July 10.

Note the Dipteran (perhaps a Sciarid, or fungus gnat) caught in the flower in the second photo. In Listera, the rostellum acts as a "trigger," such that, when it is brushed by a pollinator, a sticky fluid is ejected. This contacts the pollinia on its way to the pollinator, and quickly dries on contact with the pollinator, firmly cementing the pollinia to its body. This insect was apparently pinned by the initial "eruption," and struggled to free itself for about two or three minutes while I photographed it. After that, it broke free and flew away. Unfortunately, I was unable to catch it so the species could be determined, as the pollinator for Listera auriculata has never been recorded (at least in a published account). Indeed, this may very well be the only picture in existence of pollination in this rather uncommon species.

DISCUSSION: This species hybridizes with Listera convallarioides 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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