Tribe Pogonieae - The Pollination Biology of North American Orchids: North of Florida and Mexico - page 171

Table 9.2 Percent of flowers forming capsules in Isotria
Treatment Isotria medeoloides a Isotria verticillata b

Open pollination 83 (89) c 21

Selfing/geitonogamy 82 95

Cross-pollination 82 85 d , 92 e

Unmanipulated and bagged 67 0

Emasculated and bagged 0 0

a Vitt and Campbell ( 1997 )
b Mehrhoff ( 1983 )
c Vitt ( 1991 )
d Between populations
e Between clones in same population

Table 9.3 Data on reproduction in Isotria (Mehrhoff 1983 )
Variable I. verticillata I. medeoloides

Flower production

Total number of ramets observed 1,706 70

Number of flowering ramets 470 16

Percentage of ramets that flowered 27.5 22.9

Percentage of flowers lost 7 29

Pollination

Percentage of all flowers naturally pollinated 19.6 62.5

Percentage of all surviving flowers pollinated 21.0 83.3

Capsule production

Percentage of all flowers producing mature capsules 5.5 57.1

Percentage of pollinated flowers (capsules initiated)
producing mature capsules

43.3 80.0

Percentage of entire population (of ramets) producing
mature capsules

1.45 11.40

Mehrhoff ( 1983 ) noted some potential advantages of this strategy. First, the genet
produces a large number of closely spaced, flowering ramets, which may attract
more pollinators. In the case of I. verticillata , the percentage of pollinated flowers
was higher in larger clones. Second, the development of a number of flowering
ramets augments the number of seeds produced per genet. Third, if clones are not
isolated, the capacity for interclonal pollen flow and extensive outcrossing are
retained. Fourth, the clonal growth habit may permit the survival of the genetic
individual despite destruction of some of its ramets. Fifth, a single seed can provide
for the founding and expansion of a colony. On the negative side, the massing of
flowering ramets may be responsible for a reduction in outcrossing and an increase
in predation of the plants and capsules (Mehrhoff 1983 ). More capsules were lost to
predation in I. verticillata than in I. medeoloides (Table 9.3 ) (Mehrhoff 1983 ).
Mehrhoff ( 1983 ) chose not to conduct experimental manipulations on I. medeoloides
because of potentially destructive effects for the small populations in his study
area. Vitt and Campbell ( 1997 ), however, examined the breeding system in several,
relatively large populations in southern Maine, each with over 100 individuals.