1. Triodanis biflora (Ruíz & Pav.) Greene (small Venus’ looking-glass)
Campanula
biflora Ruíz & Pav.
Specularia
biflora (Ruíz &
Pav.) Fisch. & C.A. Mey
T. perfoliata (L.) Nieuwl. var. biflora (Ruíz
& Pav.) T.R. Bradley
Pl. 332 g; Map
1413
Stems 10–40(–50)
cm long, erect or nearly so, roughened with minute, recurved hairs along the
angles, at least toward the base. Basal leaves elliptic to obovate, tapered to
a sessile or short-petiolate base, rounded or bluntly pointed at the tip. Stem
leaves 5–20 mm long, 2–10 mm wide, 1.5–3.0 times as long as wide, elliptic to
narrowly ovate, sessile but not or 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.
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.
Calyces with the tube 3–7 mm long, usually appearing slightly inflated, the
lobes in normal flowers 5–8 mm long, narrowly triangular to lanceolate, those
in cleistogamous flowers 0.7–2.0 mm long, narrowly triangular. Corollas in
normal flowers purple to lavender, the lobes 5–9 mm long, 2–3 mm wide. Fruits
all similar in size and shape, straight and strongly ascending, 4.5–8.0 mm
long, 1.2–2.0 mm wide, the (usually) 3 pores 1.0–1.2 mm long, oval to nearly
circular, positioned at or near the tip of the fruit. Seeds 0.4–0.6 mm long,
elliptic to broadly oblong-elliptic, slightly flattened (relatively plump), the
surface smooth, shiny. 2n=56. May–June.
Scattered mostly
south of the Missouri River (southern U.S. north to Oregon, Nebraska, Illinois,
and New York). Upland prairies, glades, ledges and tops of bluffs, openings of
mesic to dry upland forests, fens, margins of ponds, lakes, and sinkhole ponds,
and banks of streams and rivers; also old fields, fallow fields, pastures,
ditches, railroads, roadsides, and open, disturbed areas.
This species is
closely related to T. perfoliata, and the two species sometimes are
found in mixed colonies. The two taxa can be crossed relatively easily
(Bradley, 1968, 1975). The hybrids are fertile, robust, and intermediate between
the parental forms in most characters, except that the inflorescence always has
more than a few open flowers, as in T. perfoliata. Bradley felt that
because the two taxa form viable hybrids both in the greenhouse and in nature,
they should be considered varieties of a single species. The alternative
interpretation was presented by Ward (1978), who noted that most plants can be
assigned to one of the parental taxa without difficulty, that several
morphological characters correlate to separate the two taxa, and that
cleistogamous flowers help to maintain the integrity of each taxon by providing
a partial genetic isolating mechanism. For these reasons, the two taxa are
maintained as separate species in the present treatment, but users should be
aware that a certain proportion of the plants in the complex encountered in the
field and herbarium cannot be determined to species with confidence.