Biology Reference
In-Depth Information
and all the plants examined bore capsules (10-45/plant) containing seed. Larson
and Larson (
1987, 1990
) suggested that the level of visitation at their study site
might be in response to a continuous or rich nectar supply. This was apparently not
the case for this orchid in western Ireland, where Duffy and Stout (
2008
) could
establish no correlation between nectar reward and visitation rates.
Additional factors influencing reproductive success in
Spiranthes
include fire,
which may stimulate flower production (Sheviak
1982
) and predation, which can be
significant in some areas. Schmidt (
1987
) found that in Nebraska populations of
S.
cernua
, predators destroyed 55% of the plants with flower buds prior to anthesis.
Antlfinger and Wendel (
1997
) also found an overall loss of 22-39% of the inflores-
cences of this species to herbivores, probably to voles. Other possible causes of
mortality in eastern Nebraska included interspecific competition and the loss of
associated fungi.
Additional Species of
Spiranthes
Ten other
Spiranthes
taxa occur in North America north of Florida and Mexico:
S.
porrifolia
Lindley (creamy ladies'-tresses),
S. stellata
P. M. Brown, Dueck, and
Cameron (no common name),
S. infernalis
Sheviak (ash meadows ladies'-tresses),
S. delitescens
Sheviak (reclusive ladies'-tresses),
S. longilabris
Lindley (giant spiral
ladies'-tresses),
S. brevilabris
Lindley (texas ladies'-tresses),
S. floridana
(Wherry)
Cory (florida ladies'-tresses),
S. eatonii
Ames ex P. M. Brown (eaton's ladies'-
tresses),
S. praecox
(Walter) S. Watson (greenvein ladies'-tresses), and
S. sylvatica
P. M. Brown (woodland ladies'-tresses), although the latter may not be distinct from
S. praecox
(Dueck and Cameron
2008
). Nothing is yet known of their pollination
biology. However, the presence of a narrow, elongated viscidium in
S. praecox
sug-
gested to Catling (
1980b
) that it is protandrous and pollinated by
Bombus.
In addi-
tion,
S. infernalis
is very similar to
S. porrifolia
, and Sheviak (
1989
) believes that it
may have evolved from it.
S. porrifolia
, in turn, was formerly recognized as a vari-
ety of
S. romanzoffiana
, an otherwise uniformly sexual species. Finally, Sheviak
and Brown (
2002
) and Brown et al. (
2008
) reported that these taxa produce exclu-
sively monoembryonic seeds, implying that the breeding system is sexual in the
populations they examined.
Other Spiranthinae
Dichromanthus Garay
Dichromanthus
includes three species distributed from the southern USA through
Mexico to Honduras. Two are present in our flora.
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