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Abstract
Fluorescence microscopy is used to compare frequencies of pollen tube penetration in in situ populations of
Cypripedium bardolphianumW.W. Smith et Farrer,
Cypripedium flavum W.W. Smith,
Cypripedium montanum Dougl. ex Lindl.,
Cypripedium parviflorum Salisbury var.
pubescens (Wildenow) O.W. Knight,
Cypripedium reginae Walter, and
Cypripedium tibeticum Schltr. The average natural (insect-mediated) pollination rates measured over five seasons are wide ranging among the six species (0.08–0.74). However, the pollination rate of hand-manipulated populations (self and/or cross) is significantly greater than the rate of insect-mediated pollinations in all species studied. A few pollen tubes in both self- and cross-pollinations display aberrant growth in the styles and/or ovaries, but their numbers are too small to suggest evidence of self-incompatibility. Pollen tubes germinate and grow up to the bases of styles within 48 h in C.
bardolphianum, C.
flavum, and C.
tibeticum. Pollen tubes remain at the bases of the styles in C.
montanum for 5 d after pollination. In C. parviflorum, pollen tubes penetrate ovaries at 7 d. Pollen tube penetration of ovaries is observed within 15 d after hand pollination in all six species but remains incomplete at this time, with the greatest number of ovule penetrations observed in C. reginae (which has the shortest floral life span). Therefore, we suggest there are additional factors aside from low pollinator visitation for low conversion rates of flowers into fruits in these Cypripedium species. These include inadequate pollen loads deposited on receptive stigmas (pollen limitation), coupled with environmental stress and/or predation disrupting or destroying the slow processes of fertilization and/or fruit maturation.
Citation
Edens-Meier, Retha; Vance, Nan; Luo, Yi-Bo; Li, Peng; Westhus, Eric; Bernhardt, Peter. 2010. Pollen-pistil interactions in North American and Chinese Cypripedium L. (Orchidaceae). International Journal of Plant Sciences. 171(4): 370-381.
