Biology Reference
In-Depth Information
known (e.g., Willems
1994
), and Porcher (
1977
) claims that reemergence may be
delayed for as long as 125 years.
Compatibility and Breeding System
Based on experimental pollinations, Medley (
1979
) found that the flowers are self-
compatible but possess no mechanism for spontaneous selfing. He reported some
revisitation of plants and flowers, indicating that selfing may occur under natural
conditions, but outcrossing among individuals of the same population was usual.
Synchronous blooming, with many plants displaying their flowers to pollinators at
the same time, may facilitate outcrossing (e.g., Willems
1994
). A number of other
Triphora
species, including
T. gentionoides
found in Florida, are known to be autog-
amous (Pridgeon et al.
2005
).
Pollination Mechanisms and Pollinators
According to Medley (
1979
), the pollinator, invariably a bee, lands on the lip and
following the ultraviolet nectar guides (Fig.
4.1a, c
), enters the floral tube to reach
the nectar at the base of the labellum. In the process, it crawls under the column
bearing the anther and stigma. As it backs out of the flower, it presumably ruptures
the rostellar membrane, and the pollinaria are glued to the rigid, backward pointing
hairs on its dorsal thorax (Fig.
4.2
). Pollination occurs when and if a bee bearing
pollinia enters another flower and deposits pollen on the stigma. The bee might
extract additional pollinia as it moves among previously unvisited flowers, and
Medley (
1979
) reported some carrying up to four sets on their thorax.
The primary pollinators of
T. trianthophora
are small, short-tongued bees of the
family Halictidae, attracted by the synchronous flowering of this orchid (Catling
1984
). Lownes (
1920
) reported pollination by
Halictus quadrimaculatus
Robertson
[=
Lasioglossum macoupinense
(Robertson)] at a site near Squam Lake in central
New Hampshire. The most important pollinator in St. Joseph County, Indiana, and
Berrien County, Michigan, was
Augochlora pura
(Fig.
4.2
) with three or four species
of
Lasioglossum
(
Dialictus
) (including
L. versans
,
L. obscurum
(Robertson), and
L. cressoni
(Robertson)) and an unknown species of
Sphecodes
and
Ceratina dupla
playing subsidiary roles (Medley
1979
). In Cass County, Michigan, two other halic-
tids,
L.
(
Evylaeus
)
quebecense
(Crawford) and
L. illinoense
(Robertson) functioned as
primary pollinators even though
A. pura
was present at the site (Medley
1979
). Keenan
(
1996
) also collected several insects visiting
Triphora
flowers in New Hampshire,
including an unidentified species of
Andrena
bee with purple pollinia on its back.
Medley (
1979
) listed a large number of additional, nonpollinating flower visi-
tors. For example, bumblebees (
Bombus
) visited the flowers occasionally but were
ineffective pollen vectors. The plants were unable to support their weight, and the
bees departed the collapsing stems without removing any pollen or nectar. Willems
(
1994
), however, reported that an unidentified, small species of bumblebee (
Bombus
)
removed pollinia from a flower in western Massachusetts. Occasionally, late in the
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