Tribe Neottieae - The Pollination Biology of North American Orchids: North of Florida and Mexico - page 56

Hemisphere. Eight are found in our flora, but detailed accounts of pollination biology
are available only for L. cordata and the Eurasian species, L . ovata (L.) R. Br. The
latter is now also found in Ontario (Magrath and Coleman 2002 ), but its reproduction
in North America has not been studied.
Listera cordata (L.) R. Brown (Heart-Leaved Twayblade)
Distribution and Habitat
L. cordata is a common but inconspicuous and often overlooked orchid of moist
sphagnum hummocks in northern woods and cold balsam-cedar-spruce bogs, but is
also found in thick, rather dry moss mats on headlands and in the humus or needle-
duff of deciduous and coniferous forests (Case 1987 ). It is circumboreal in distribu-
tion. In North America, it ranges from Greenland and Labrador south to Virginia
and west to Alaska and northern California. Southern extensions occur in the Rocky
Mountains to New Mexico and in the Appalachians to North Carolina (Luer 1975 ;
Magrath and Coleman 2002 ).
Floral Morphology
Variable numbers of small, light green to purple resupinate flowers are borne in a
slender, terminal raceme (Fig. 3.1a ; Table 3.1 ) (Ackerman and Mesler 1979 ; Magrath
and Coleman 2002 ). Individual flowers persist for 10-25 days (Ackerman and
Mesler 1979 ). The linear-oblong lip, flattened and bent sharply downward from a
point near its insertion, is deeply cleft at its apex into two linear-lanceolate lobes
(Fig. 3.1b, c ). A short, erect to arcuate column is positioned in the center of the
flower. The anther is suberect and located near the apex of the column behind a
large, thin, leaf-like rostellum. It dehisces in the bud and two soft and mealy, club-
shaped pollinia containing numerous tetrads are released (Dressler 1993 ). A vis-
cidium and a caudicle are absent, and the pollinia are held unattached and enfolded
by the incurved margins of the rostellum (Fig. 3.1d ) (Ackerman and Mesler 1979 ).
The stigma is entire and located directly beneath the rostellum (Fig. 3.1f ). A narrow
nectary or nectar groove extends down the center of the labellum for most of its
length (Fig. 3.1c ); a second nectary is present on a basal disk immediately below the
column (Ackerman and Mesler 1979 ).
Compatibility and Breeding System
A number of authors have reported autogamy or apogamy in Listera (e.g., Hooker
1854 ; von Kirchner 1922 ; Hagerup 1952 ; Kugler 1970 0ROCHAZKAAND6ELISEK
1983 ), and indeed Lojtnant and Jacobsen ( 1976 ) found the fruiting to be so abun-
dant and widespread in Greenland populations of L. cordata that they supposed this