Tribe Triphoreae - The Pollination Biology of North American Orchids: North of Florida and Mexico - page 86

Table 4.1 Data on Triphora (Medley 2002 )
Character Triphora trianthophora

Plant height (cm) 7-20 (−30)

Flower number/raceme (1-) 3-6 (−20)

Dorsal sepal (mm) 11-15 × 3-4

Lateral sepals (mm) 11-15 × 3-4

Lateral petals (mm) 11-14 × 3-4

Lip (mm) 8-20 × 6-10

Column (mm) 10 × 2

Chromosomes (2n) 18 a , 44 b

a Brackley (1985)
b Dressler (1981) for tribe Triphoreae

Triphora trianthophora (Swartz) Rydberg
(Three Birds Orchid, Nodding Pogonia)

Habitat and Distribution

T. trianthophora is distributed throughout eastern North America from southwest
Maine to southern Ontario and Iowa south to central Florida and east Texas (Luer
1975 ). It is apparently found in a wide variety of usually shady habitats, including rich
or sandy mesophytic or dry woodlands, dune forests, sandy flatwoods, floodplain for-
ests, and tamarack swamps (Medley 1979, 2002 ; Keenan 1986 ; Ramstetter 2001 ).

Floral Morphology

Generally, six or fewer resupinate flowers are borne singly in the upper leaf axils
(Table 4.1 ) (Medley 1979 ). They are gaping, nodding to nearly erect, and white,
often tinged with pale pink (Luer 1975 ; Medley 2002 ). The dorsal sepal is erect, the
laterals spreading (Fig. 4.1a ). The lip is obovate, narrowly clawed, and three-lobed
(Fig. 4.1c ). The lateral lobes are ovate to ovate-triangular and entire. Along with the
closely overarching lateral petals, they form a floral tube enclosing the column
(Fig. 4.1a, b ). The middle lobe is ovate to orbicular with a sinuous to denticulate
margin. Three parallel, bright green, papillose crests extend from the claw to about
half way down the length of the central lobe (Fig. 4.1a, c ). The green crests along
with a narrow strip extending from the crests to the distal end of the labellum fluo-
resce in ultraviolet and serve as nectar guides (Medley 1979 ). The column is white
and bears a pale green to white, two-chambered anther with magenta margins
(Fig. 4.1d, e ). The anther is rigid, terminal, and incumbent and contains two red-
dish-purple, soft, and mealy pollinia comprised of tetrads and held together by viscin
(Lownes 1920 ; Medley 1979, 2002 ). A drop of rostellar glue is covered by a fragile
membrane (Dressler 1993 ); caudicles and true viscidia are not present (Freudenstein
1994 ). The stigma, positioned beneath the column just proximal to the anther,
is 1-1.5-mm long with a flat, granular, viscid surface (Fig. 4.1d, e ). The flower