Clasping Venus’ Looking Glass (Triodanis perfoliata; formerly, Specularia perfoliata) of the Bellflower (Campanulaceae) family is an erect to reclined annual forb with clasping, ovate to orbicular leaves and both non-opening (cleistogamous – CL) flowers and opening (chasmogamous – CH) flowers. The genus name, based on Greek words for “three” and “tooth”, refers the typical number (3) of calyx lobes of CL flowers. The specific epithet, based on Latin, refers to the clasping bases of the sessile leaves which are seemingly perforated by the stem. The common name is a reference to a similar-looking European species [Venus’ Looking Glass (Legousia speculum)] which has relatively large, shiny seeds said to resemble a mirrored looking-glass. In the U.S., other than Nevada, this species occurs within all 48 contiguous states and extends into Canada and Mexico and into South America, including Argentina. In Arkansas, it occurs statewide. Habitats include sunny to partially sunny sites with various, well-drained sandy to rocky soils where soils are sufficiently exposed to allow the tiny seeds to germinate; including, such sites in prairies, glades, woodland openings, rocky outcrops, trails and old fields. Plants have a spreading, branching, rather stubby, white taproot system.

This herbaceous winter annual germinates in autumn and in winter has a basal rosette of broadly ovate, petiolate leaves with hispid pubescence. In late spring, a single main stem appears, which eventually reaches a height of 4-18 inches; however, in sunny habitats, main stems may grow to 30+ inches. Bases of main stems are to 3/16 inch wide. When mature plants remain small, they only have the single stem, but larger plants may have several to a half dozen secondary stems growing from lower leaf axils of the main stem (one stem per node). Secondary stems are ascending to widely spreading and have lengths from near 0 (see Photo 14) to 16+ inches. Secondary stems, which do not grow tertiary stems, remain shorter than main stems and are less stout. The light green stems have 5 straight ridges, with long hispid hairs, extending from stem-base to stem-apex. Main and secondary stems typically terminate with CH flowers, often a central flower and a pair of lateral flowers. Flowers develop in leaf axils of even the smallest plants with most or all of these being of the CL type. When stems grow without support, they become reclined and twisty. Stems and leaves produce a small quantity of milky sap.

Stems have regularly spaced ovate to orbicular leaves from stem base to apex, with leaf size decreasing distally. Each leaf is rotated about 70⁰ from the next so that the straight ridges connect to the base of every-other leaf. The leafy stems have a columnar appearance when younger. All leaf axils bear axillary buds of which, typically, the lowermost buds remain dormant, followed by buds that develop into secondary stems (if any), followed by axils with 1-3+ buds that develop into CL, followed by axils that produce one to several CH flowers. CL and CH flowers generally occur in separate leaf axils, but in the transitional zone between the two types, both may occur in the same axils. When multiple flowers occur in an axil, flowers reach anthesis successionally. Small plants and those growing in shade may have CL flowers only. Plants bearing CH flowers may revert to producing CL flower if growing conditions deteriorate.

Cauline leaves are light green. Lowermost cauline leaves are elongate-ovate with short petioles, with more distal leaves becoming ovate to ovate-cordate, sessile and strongly clasping. Largest leaves, to an inch long and wide, are just above stem-base with size gradually decreasing to stem apex. Blades of clasping leaves are ascending away from the midrib and sunken toward their bases so that blades are cupped. While leaf margins of weaker plants are entire, those of more robust plants have mostly smooth margins with four or so broad, very short teeth. Blades may be wavy to ruffled. Apexes of larger leaves are rounded to acuminate. Palmate venation, more pronounced on leaves from sunny sites, is recessed above (adaxially) and expressed below (abaxially) with the 3-6 secondary veins terminating at the base of marginal teeth. Leaves may be glabrous on the upper surface or may be minutely pubescent while the lower surface has short hairs (especially on veins), and leaf edges are ciliate. All except basal and lowermost cauline leaves remain viable until plants reach senescence in late spring at which time the entire plant becomes scraggly and soon dies. Cauline leaves of small plants are not clasping.

Both CL and CH flowers have elongate, fluted, glabrous, light green calyxes rimmed with prominent, spreading, narrowly triangular lobes. Calyxes of CL flowers have 3-4+ lobes while CH flowers typically have 5 lobes. CH calyxes are 2-3 times larger than CL calyxes. The tiny, closed CL flowers (with minute sepals and stamens) are barely visible to the naked eye. Calyx lobes of CH flowers alternate with corolla lobes. The colorful CH flowers have a corolla, ½ to ¾ inch wide, with 5 petal-like spreading corolla lobes (united at their bases), 5 stamens (filaments + anthers) and a pistil (ovaries + style + stigma). The lavender to violet corollas, marked with longitudinal dark lines (insect guides) have white throats, stigmatic surfaces and stamens. The elongate, slim, ivory anthers are set sleeve-like on short white filaments. The stout style protrudes well above the anthers at anthesis and is white along its lower portion and lavender to violet along its upper portion. The lavender to brown stigma is club-like with a roughened surface when closed but, when recurved, reveals 3 white stigmatic surfaces.

Buds of CH flowers first become apparent as white, heavily ribbed “footballs” set atop calyxes – – ribs fitting between calyx lobes. With approaching anthesis, buds become lavender. Late in the bud-stage, the vertically positioned anthers are pressed tightly against upper portion of the style – – below the closed stigma-head. Anthers dehisce so that pollen is available for transfer to the hair-lined style as it elongates. The depleted anthers spread away from the style-stigma and shrivel. With corolla lobes spread wide, insects collect pollen from the style and, with sufficient insect activity, style-hairs retract. Later, the stigma-head opens and recurves so that three, elongate stigmatic surfaces are well exposed for pollination (preferably by pollen from other plants). Flowers have 2-3 chambered ovaries.

Calyxes (on capsules) dry shortly after anthesis. The oblong-cylindric capsules have 2-3 flaps at mid-capsule that roll-up to expose oval pores. With slight movement, tiny, dull to slightly shiny, dark brown, ovoid seeds fall from capsules. The larger CH capsules may contain 150+ seed. Capsules of earlier flowers are dropping seeds as stems continue to grow and produce additional flowers. Along with seed dispersal by water run-off, the tiny seeds are probably also dispersed by wind. Both CL and CH flowers produce viable seed.

In regard to native plant gardening, this wide-spread winter annual may not be a good choice in a formal garden. In a natural setting, it may already be established. It is an interesting winter annual. Its small showy CH flowers provide color and supports various bees, flies and small butterflies. Seeds are probably too small for birds or small mammals. Large plants are rather scraggly with senescence but should disappear by summer. Should it be too aggressive, removal of some plants would be necessary in early spring.

Three additional species of the genus have been recorded in Arkansas. In comparison to T. perfoliata, these are:

1) Slim-Pod Venus’ Looking Glass (T. lamprosperma): Most similar. Has clasping leaves with flowers and similar calyxes except pores are just below lobes. Seeds are twice as large and shiny.

2) Prairie Venus’ Looking Glass (T. leptocarpa): Leaves are linear to oblanceolate and calyxes have long, slim lobes.

3) Small Venus’ Looking Glass (T. biflora, sometimes treated as a variety or subspecies of T. perfoliata): Has narrower, mostly non-clasping leaves. Leaves have acute tips with entire to scalloped margins. Elongate capsules have pores just below the calyx lobes.

Article and photographs by ANPS member Sid Vogelpohl

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