5. Triodanis perfoliata (L.) Nieuwl. (clasping Venus’ looking-glass)

Campanula perfoliata L.

Specularia perfoliata (L.) A. DC.

Pl. 3332 c–e; Map 1417

Stems 10–80(–100) cm long, erect or ascending, sometimes from a spreading base, often short-hairy along the angles, sometimes roughened with minute, recurved hairs toward the tip. Basal leaves broadly elliptic to broadly ovate, angled or tapered to a sessile or short-petiolate base, rounded or bluntly pointed at the tip. Stem leaves 5–20(–25) mm long, 4–20(–27) mm wide, mostly as long as wide or slightly wider than long (the uppermost ones sometimes slightly narrower), broadly ovate to somewhat kidney-shaped, sessile, rounded to cordate and clasping the stem, rounded to bluntly pointed at the tip, the margins finely and bluntly to sharply toothed, the upper surface glabrous or nearly so, the undersurface finely roughened or with relatively soft, short hairs. Flowers 1–3 per node at most nodes of the stem, mostly cleistogamous but normal, open flowers usually 1 per node along the upper 1/3–2/3 of the stem. Calyces with the tube 3–5 mm long, usually appearing slightly inflated, the lobes in normal flowers 4–9 mm long, narrowly triangular to lanceolate, those in cleistogamous flowers 2–3 mm long, narrowly triangular. Corollas in normal flowers purplish blue to purple, rarely with white streaks or entirely white, the lobes 4–7 mm long, 2–3 mm wide. Fruits all similar in size and shape, straight and strongly ascending, 5–10 mm long, 2–3 mm wide, the (usually) 3 pores 1.3–2.0 mm long, elliptic, positioned below the midpoint of the fruit. Seeds 0.4–0.7 mm long, elliptic to broadly oblong-elliptic, slightly flattened (relatively plump), the surface minutely wrinkled or tuberculate, dull or only slightly shiny, rarely smooth and shinier. 2n=56. May–June.

Scattered nearly throughout the state (U.S., Canada, Mexico, South America, Caribbean Islands). Upland prairies, glades, ledges and tops of bluffs, openings of mesic to dry upland forests, oxbows, marshes, margins of lakes, and banks of streams and rivers; also old fields, fallow fields, pastures, ditches, railroads, roadsides, and open, disturbed areas.

Rare individuals with white corollas have been called f. alba (J. Voigt) Steyerm. Triodanis perfoliata is by far the most widespread species in the genus and is found in the broadest variety of habitats. It is closely related to T. biflora and hybridizes readily with that species (Bradley, 1968). See the treatment of T. biflora for further discussion. Bradley also discussed possible hybridization with T. leptocarpa in southwestern Missouri and Mercer County (and in other states), as well as rare putative hybrids with T. holzingeri from Oklahoma.

McVaugh (1945) suggested that smooth-seeded plants (rare in Missouri) are polyploids that have spread north and south from the original distribution, but to date there exist no counts to differentiate these populations, and the species appears to be uniformly tetraploid (2n=56). Interestingly, Trent (1942) recorded that seed viability in populations of T. perfoliata that he studied was relatively low and different for normal and cleistogamous flowers: normal flowers produced about 47.5 percent viable seed, whereas in cleistogamous flowers only about 0.07 percent of the seed was viable. His anatomical studies documented that for both flower types nonviable seeds lacked embryos. The cause for this unusual situation has not been determined.