Tribe Pogonieae - The Pollination Biology of North American Orchids: North of Florida and Mexico - page 181

suggests the possibility of pollinator limitation (Gregg 1989, 1991a ). Other charac-
teristics of Cleistesiopsis suggesting pollinator limitation include an extended period
of female receptivity in both unpollinated flowers and those receiving low pollen
dosages and the ripening of capsules containing relatively few seeds (Willson and
Schemske 1980 ; Gregg 1991a ). In addition, anthesis is timed to occur in mid to late
June in the West Virginia population of C. bifaria when few other plants are in
bloom (Gregg 1989 ).
Despite adaptations to avoid the deleterious effects of geitonogamy in C. bifaria ,
such crosses undoubtedly occur in a plant that produces more than one flower per
stem and a number of simultaneously flowering ramets. However, as Mehrhoff
( 1983 ) noted for Isotria, the potentially disadvantageous effects of such a breeding
system might be compensated, where pollinator visitation is a significant limiting
factor because the aggregation of flowering stems increases the probability that pol-
linator visits will occur, however brief or uncommon (Gregg 1989 ).
Cleistesiopsis bears a maximum of about 20,000 seeds per capsule rather than the
hundreds of thousands or millions produced by many other orchids (Gregg 1991a ).
Moderate seed yields may be beneficial in a plant like Cleistesiopsis with a small amount
of storage tissue. Less drain occurs on the nutrient resources of the plant at a time when
capsule maturation and the production of next year's primordia are proceeding simulta-
neously. An absence of within season resource limitation is suggested by low levels of
capsule abortion regardless of pollen dosage (Willson and Schemske 1980 ; Gregg
1991a ) and an absence of any second year reduction in flowering and fruiting in a large
sample of plants that produced capsules the first year (Gregg 1989 ). Long-term studies
are needed to examine the possibility of lifetime resource limitation.
Fruit set over 50% has been reported in other nonrewarding orchids (Steiner et al.
1994 ; Nazarov 1995 ), and further study of the pollination dynamics in such species
may help to explain the frequency of seemingly inefficient deceptive pollination sys-
tems in this family (Lipow et al. 2002 ). Gregg ( 1991b ) recommends further investi-
gation of the relationships between insects and nectarless orchids with mealy or soft
pollinia currently presumed to employ a deceit strategy to achieve pollination.
The limiting effect of herbivore damage was examined in West Virginia (Gregg
1989 ). The damage was minimal in 5 years of a 7-year study. In the two remaining
years, grazing, most likely by deer, had a significant impact, destroying about 30%
of the plants 1 year. Among flowers that set fruit that year about 85% produced
mature capsules. Insect damage, deer predation, and fungal infection accounted for
most of the losses.
References
Ackerman JD (1975) Reproductive biology of Goodyera oblongifolia (Orchidaceae). Madrono
23:191-198
Ackerman JD (1981) Pollination biology of Calypso bulbosa var. occidentalis (Orchidaceae): a
food-deception system. Madrono 28:101-110
Ackerman JD (1986) Mechanisms and evolution of food-deceptive pollination systems in orchids.
Lindleyana 1:108-113