Triodanis biflora (Ruiz & Pav.) Greene

Small Venus' Looking-Glass

Triodanis biflora plant

Family - Campanulaceae

Stems - From a taproot, multiple from the base, simple, glabrous, green, to +60cm tall, +/-2mm in diameter, erect to ascending, with whitish sap, winged from decurrent leaf tissue. Wings to .2mm broad, with spreading to retrose minute prickles (use a lens to see).

Triodanis biflora stem

Leaves - Alternate, sessile. Lowest 2-4 leaves spatulate, all other leaves ovate to lanceolate, acute, shallow crenate-serrate (the teeth with white tips), glabrous adaxially, mostly glabrous abaxially but with minute straight prickles on the veins. Lowest leaves to 2cm long, +/-1cm broad. Cauline leaves gradually reduced upward. those in the middle of the stem +/-1.5cm long, +/-1cm broad, nearly always somewhat folded (conduplicate).

Triodanis biflora leaves

Inflorescence - Cleistogamous flower in every leaf axil, single, paired, or in 3's, sessile, each usually subtended by a minute subulate bract. Chasmogamous flowers produced in the most apical 1-3 leaf axils only, sessile, with a larger hypanthium than the cleistogamous flowers.

Flowers - Corolla purple, 5-lobed, to +/-1.5cm broad. Lobes glabrous, 6-8mm long, 2-4mm broad. Corolla tube 1-1.5mm long. Stamens 5, alternating with the corolla lobes. Filaments translucent, expanded at the base, ciliate on the margins basally, to +1mm broad at the base, thin and twisted in the apical 2/3, to 2mm long. Anthers yellow, to +2mm long, .4mm broad, linear. Style 1, +/-5mm long, whitish basally, purple apically, with a few small hairs apically. Stigmas 3, spreading, +/-1mm long. Ovary many-ovuled, 3-locular, placentation axile. Hypanthium (of chasmogamous flowers) green, to 1cm long, 2-3mm in diameter, glabrous. Sepals 5, subulate to lanceolate, acuminate, 5-7mm long, +/-2mm broad, spreading, glabrous, with a single midrib below. Sepals on cleistogamous flowers smaller than those of the chasmogamous flowers and usually unequal. Hypanthium of the cleistogamous flowers with a few minute prickles.

Triodanis biflora flowerChasmogamous flower.

Triodanis biflora flowerAgain.

Triodanis biflora calyxCalyx of chasmogamous flower.

Triodanis biflora flowerCleistogamous flowers.

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 pores 1.0-1.2 mm long located just beneath the sepals. Seeds brown, shiny, .5-.6mm long, ellisoid to orbicular, falling from pores.

Triodanis biflora fruitsFruits, with arrows pointing to pores.

Flowering - April - June.

Habitat - Rocky open glades, prairies, openings in ridgetops, open ground along streams, fields, pastures, roadsides, waste ground.

Origin - Native to U.S.

Other info. - This small but showy species can be found in the southern half of Missouri. The plant is easy to identify becasue of the cleistogamous flowers in nearly every leaf axil. The chasmogamous flowers are only found in the most apical 1-3 leaf axils. In addition, the leaves are longer than wide, and the fruit pores are located near the tips of the fruits. With age, the plant gets long and thin and the stems recline on the ground.
A formerly used genus name was Specularia.

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 (SRTurner).