Autogamous fruit set in a mycoheterotrophic orchid Cyrtosia septentrionalis
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Non-photosynthetic mycorrhizal plants (i.e. mycoheterotrophs) have long attracted interest due to their bizarre morphological features. Nonetheless, few studies have reported on the reproductive biology of these mycoheterotrophs. In the present study, the pollination mechanism of the mycoheterotrophic orchid Cyrtosia septentrionalis (Rchb.f.) Garay in central Japan was investigated. In spite of their showy appearance, flowers of C. septentrionalis failed to attract pollinators and possessed an effective self-pollination system, in which the rostellum was poorly developed and lost the ability to physically separate the stigma and pollinia, thus allowing contact between them. Comparable fruit set ratio was also obtained in bagged plants and following induced autogamous and xenogamous pollinations. These results indicate that the species is capable of outbreeding, but self-compatible and not pollinator-limited for fruit set under natural condition. These pollination mechanisms may be adaptations to survive the shaded and sparse herbaceous understory, where insect-pollinators are limited.
KeywordsAutogamy Mycoheterotroph Orchidaceae Pollination biology Reproductive biology Self-pollination
I thank Sayoko Mori for fieldwork support, Dr. Utsugi Jinbo for moth larvae identification; and Drs. Makoto Kato and Atsushi Kawakita for constructive advises on this study.
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