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Fig. 3.1
Listera cordata
. (
a
) Habit, scale bar = 1 cm; (
b
) flower, side view; (
c
) flower, front view,
scale bars (
b
,
c
) = 1 mm; (
d
)-(
f
) front view of column; (
d
) rostellum intact; (
e
) column after trig-
gering of rostellum and release of the pollinia; (
f
) column with an elevated rostellum and exposed
stigma, scale bar = 0.3 mm.
an
anther,
po
pollinia,
ro
rostellum,
sg
stigma,
tr
trigger hairs. (
d
)-(
f
)
after Ackerman and Mesler (
1979
) with permission
species might also have such a breeding system. However, the tetrads of
L. cordata
are more coherent, less likely to fragment, and less likely to autopollinate than those
of other
Listera
while cross-pollination is common and appears to be favored.
Melendez-Ackerman and Ackerman (
2001
), for example, found that subalpine
populations in Gunnison County, Colorado, although also self-compatible, pro-
duced a significantly higher percentage of fertilized ovules and more seeds per cap-
sule when cross-pollinated. Similarly, Ackerman and Mesler (
1979
), in a 3-year
study in Humboldt County, California, found that geitonogamy occurred but out-
crossing was promoted by protandry, and Mesler et al. (
1980
) estimated the relative
frequency of geitonogamous versus xenogamous pollination in northern California
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