Tribe Neottieae - The Pollination Biology of North American Orchids: North of Florida and Mexico - page 65

enclosed flowers produced fruit. He also observed cross-pollination, and similar
reports are available for a number of Old World species of Cephalanthera , where
hybridization, autogamy, and apomixis have also been recorded (Darwin 1862 ;
Godfery 1933 ; Evans 1934 ; Hagerup 1952 ; Dafni and Ivri 1981 ; Nilsson 1983 ;
0ROCHAZKAAND6ELISEK 1983 ; Scacchi et al. 1991 ).
Pollination Mechanism and Pollinators
Kipping ( 1971 ) reported that autogamy was frequent in older flowers following the
withering and dehiscence of the anther caps. The basal section of the labellum also
pulled away from the column as the flowers aged, and the pillars of mealy pollen,
left unsupported, often fell over, sometimes landing on the viscid stigma.
Kipping also reported insect pollination. During the first year of his study, he
captured three, small halictid bees, Lasioglossum pullilabre (Vachal) [cited as
Evylaeus pullilabris (Vachal)], on the flowers of C. austiniae . Two carried the white
pollinia of this orchid glued to their thoraxes. The third carried no pollinia, but the
flower from which it had just emerged bore two strands of white pollen on its stigma.
The bees, after hovering momentarily before a flower, landed on the distal section
of the lip. Each, then, entered the narrow opening between the column and concave
basal section of the lip (Fig. 3.3a ), where it remained for 10 or 15 s. While backing
out, the bee's thorax contacted the stigma and acquired a deposit of viscid material.
As it passed under the anther, some of the pollen adhered to this deposit and was
extracted. A second species, Lasioglossum nigrescens ( Craeford ) [as Evylaeus
nigrescens (Crawford)], also captured on a flower of C. austinae , carried no
pollinia.
Based on these observations, C. austinae would appear to be a nonrewarding,
facultatively autogamous orchid employing a strategy of deceit to attract pollina-
tors. Although floral mimicry is involved in the attraction of insects to some nonre-
warding, Old World species of Cephalanthera (e.g., Dafni and Ivri 1981 ; Nilsson
1983 ; Nazarov and Ivanov 1991 ), there is no evidence for or against mimicry in C.
austinae. Moreover, the flowers may not always be unrewarding. Kipping ( 1971 )
observed a distinctly different behavior during the second year of his study when
another species of halictid bee, Lasioglossum nevadense (Crawford) (as Dialictus
nevadensis Crawford), visited the flowers in large numbers. After landing on the lip,
this bee immediately crawled into its concave basal section, ascended the column to
the anther, removed pollen with its mandibles and front legs, and transferred the
grains to its hind legs and the ventral surface of its abdomen. In the course of its
visit, the bee often crawled randomly over the surface of the column, and subse-
quent examination revealed the presence of white pollen on several stigmas (Kipping
1971 ). The levels of self-pollination versus cross-pollination were not determined,
but either way this appears to be a case where orchid pollen is deliberately collected
by an insect and pollen transfer is not achieved by deceit. Such behavior has been
reported elsewhere in North America only in Cleistesiopsis , possibly Calopogon
(Gregg 1991 , see below) and Cypripedium (Light 2005 ).