Tribe Pogonieae - The Pollination Biology of North American Orchids: North of Florida and Mexico - page 170

Fig. 9.2 Isotria medeoloides . ( a ) Flower, front view; ( b ) Column, oblique ventral view showing
pollen mass in contact with the stigma, scale bars = 2 mm. an anther, po pollen mass, sg stigma
from 4 to 12 days in North Carolina, opening 1-2 weeks later than those of I. verticil-
lata , where the species are sympatric (Mehrhoff 1983 ).
Compatibility and Breeding System
In a study of I. verticillata in the southeastern United States, Mehrhoff ( 1983 ) found that
capsule development was initiated in 95% of flowers that were artificially self-pollinated
or “cross-pollinated” within a clone, 92% of flowers that were artificially cross-pollinated
between clones in the same population, 85% of flowers that were artificially cross-pol-
linated between populations, 0% of flowers that were enclosed in an insect-proof mesh
bag, and 0% of flowers that were emasculated and similarly enclosed (Table 9.2 ). I.
verticillata is therefore self-compatible, potentially allogamous, and shows no evidence
of autogamy or agamospermy. It is a clonal orchid with a xenogamous-geitonogamous
breeding system very similar to that found in Goodyera (q.v.) (Ackerman 1975 ; Kallunki
1981 ). This kind of breeding system may represent an effective adaptation to pollinator
scarcity, but not pollinator absence (Ames 1922 ; Mehrhoff 1983 ).