Triodanis biflora (Ruiz & Pav.) Greene

Small Venus' Looking-Glass

Triodanis_biflora_plant.jpg
STATS

Native
CC = 3
CW = 5
MOC = 36

© DETenaglia

Family - Campanulaceae

Habit - Annual forb from a taproot. Sap milky.

Stems - Variably ascending to erect, to 50 cm, sometimes multiple from the base, roughened with minute, recurved hairs along the angles, at least toward the base.

Triodanis_biflora_stem.jpg Stem.

© DETenaglia

Triodanis_biflora_stems.jpg Stems and leaves.

© SRTurner

Triodanis_biflora_stem1.jpg Stem with fruits.

© SRTurner

Leaves - Alternate, sessile. Stem leaves 5-20 mm long, 2-10 mm wide, gradually reduced upwards, 1.5-3.0 times as long as wide, elliptic to narrowly ovate, sessile but at most only slightly clasping the stem, mostly bluntly pointed at the tip, the margins finely scalloped or bluntly toothed to nearly entire, the upper surface glabrous or nearly so, the undersurface finely roughened or with relatively soft, inconspicuous hairs, mostly along the veins.

Triodanis_biflora_leaf1.jpg Leaf adaxial.

© SRTurner

Triodanis_biflora_leaf2.jpg Leaf abaxial.

© SRTurner

Triodanis_biflora_leaves.jpg Pressed leaves.

© DETenaglia

Inflorescences - Flowers 1-3 per node at most nodes of the stem, mostly cleistogamous, the normal open-flowering one(s) usually solitary (rarely 2 or 3) at the stem tip.

Triodanis_biflora_inflorescence.jpg Inflorescence. This many concurrently open flowers is unusual.

© SRTurner

Flowers - Calyces with the tube 3-7 mm long, usually appearing slightly inflated. Chasmogamous flowers with 5 lobes, these 5-8 mm long, narrowly triangular to lanceolate. Cleistogamous flowers with 3-4 lobes, these 0.7-2.0 mm long, narrowly triangular. Corollas in normal flowers 5-lobed, purple to lavender, the lobes 5-9 mm long, 2-3 mm wide. Corolla tube 1.0-1.5 mm long. Stamens 5, alternating with the corolla lobes. Filaments translucent, expanded at the base, ciliate on the margins basally, to 1 mm broad at the base, thin and twisted in the apical 2/3, to 2 mm long. Anthers yellow, to 2 mm long, 0.4 mm broad, linear. Style 5 mm long, whitish basally, purple apically, with a few small hairs apically. Stigmas 3, spreading, 1 mm long. Ovary many-ovuled, 3-locular, placentation axile. Hypanthium (of chasmogamous flowers) green, to 1cm long, 2-3mm in diameter, glabrous.

Triodanis_biflora_flowers1.jpg Flowers (Chasmogamous).

© SRTurner

Triodanis_biflora_flower2.jpg Flower (Chasmogamous).

© SRTurner

Triodanis_biflora_flower.jpg Chasmogamous flower.

© DETenaglia

Triodanis_biflora_calyx.jpg Calyx of chasmogamous flower.

© SRTurner

Triodanis_biflora_flower3.jpg Cleistogamous flowers.

© DETenaglia

Fruits - Fruits all similar in size and shape, straight and strongly ascending, 4.5-8.0 mm long, 1.2-2.0 mm wide, with (usually 3) oval to round pores 1.0-1.2 mm long located just beneath the sepals. Seeds brown, smooth, shiny, .5-.6mm long, ellisoid to orbicular, falling from pores.

Triodanis_biflora_diagram.jpg Immature fruit, with pore still covered by membranous tissue and not yet open.

© SRTurner

Triodanis_biflora_fruit1.jpg Mature fruit, clearly showing dehiscence pore.

© SRTurner

Flowering - May - June.

Habitat - Upland prairies, glades, ledges and tops of bluffs, forest openings, fens, pond margins, streambanks, fields, pastures, ditches, railroads, roadsides, and open, disturbed areas.

Origin - Native to the U.S.

Other info. - This little plant is often overlooked or ignored, partly because it is small and not very showy, and partly because it sometimes inhabits disturbed areas. Nevertheless, it is a distinctive member of our native flora. In Missouri it is mainly found in counties south of the Missouri River. Beyond Missouri it occurs throughout the southeastern quadrant of the continental U.S., and also numerous counties along the U.S. southern border and Pacific Coast. It is recognized by its sessile leaves along unbranched stems, and its purple flowers. An important character for identification of any species of Triodanis is the location and shape of the dehiscence pore. In T. biflora this is oval or round, and positioned at the top of the fruit, just beneath the sepal bases. The plant has the curious habit of forming mostly cleistogamous flowers (i.e., flowers which remain closed and are self-fertile). With age, the plant gets long and thin and the stems often recline on the ground.

A formerly used genus name was Specularia. The species has also been considered a subspecies (ssp. biflora) of Triodanis perfoliata.

Photographs taken in off Lee Rd 54, Lee County, AL., 4-21-05 (DETenaglia); also at Coon Island Conservation Area, Butler County, MO, 5-19-2014, Otter Slough Conservation Area, Stoddard County, MO, 5-29-2020, and Tingler Prairie Natural Area, Howell County, MO, 6-10-2021 (SRTurner).