Tribe Calypsoeae - The Pollination Biology of North American Orchids: North of Florida and Mexico - page 108

explain conflicting reports in the literature, where the odor of both varieties has been
variously described as faint or strong, sweet and rose-like (variety occidentalis ) or not
rose-like (both varieties) or completely absent (Bradshaw 1919 ; Mousley 1924 ;
Kipping 1971 ; Stoutamire 1971 ; Luer 1975 ; Krell 1977 ; Boyden 1982 ).
6EGETATIVEREPRODUCTIONANDCLONALGROWTHAREFARMORECOMMONINVARIETY
a mericana than in variety occidentalis (Mousley 1924, 1925 ; Krell 1977 ). Krell
( 1977 ) found that patches of variety occidentalis in northwestern Idaho usually con-
tained three to nine plants in an area of one square meter or less. Such patches only
occurred in densely shaded areas, where there was little interspecific competition.
In areas that received more light, groups consisted of no more than two or three
plants, and these were much more widely spaced. This contrasts with reports of
large, dense clones of variety a mericana (Mousley 1925 ; Mosquin 1970 ). Terrill
(in Mousley 1925 ), for example, reported up to 50 plants in a 1 m 2 area.
Compatibility and Breeding System
Both varieties are self-compatible but not autogamous. Ackerman ( 1981 ) examined
the breeding system of variety occidentalis in Humboldt County, California. He
obtained 100% fruit set and 81.6% viable seed in artificially self-pollinated, caged
plants. Unmanipulated, caged plants failed to set any fruit. Artificially self-polli-
nated flowers in Marin County, California (Kipping 1971 ), and northwestern Idaho
(Krell 1977 ) also developed fruit. In a study of variety americana at Banff National
Park, Alberta, Mosquin ( 1970 ) found that self-pollinated plants, bagged to exclude
insects, produced fruit and abundant seed, while unmanipulated plants, so treated,
did not. Although the pollinaria are easily removed, in the absence of a visitor they
remain in position until the flower withers; the relative positions of the anther and
stigmatic surface are thought to minimize the chances of self-pollination.
Pollinators and Pollination Mechanisms
Insects captured bearing pollinaria or viscidia of C. bulbosa in North America are
listed in Table 6.2 along with references and collection sites. All were bumblebees,
mostly Bombus (including Psithyrus ) queens, and the flowering of Calypso is coin-
cident with their emergence (e.g., Boyden 1982 ). The flowers usually bloom before
the workers appear in large numbers, and in many cases only queens are large
enough to act as effective pollinators (Mosquin 1970 ; Ackerman 1981 ; Boyden
1982 ). However, due to variation in the size of the lip opening, larger workers some-
times transfer pollen, particularly in variety americana (Table 6.2 ) (Mosquin 1970 ,
Thorp, personal communication in Ackerman 1981 ; Boyden 1982 ). The varieties are
not isolated from one another by specialized or exclusive pollinators, and although
purportedly allopatric, it is likely that some populations overlap in northwestern
North America (Sheviak and Catling 2002 6ARIETALINTERCOMPATIBILITYISLIKELYBUT
has apparently not yet been tested experimentally.