Abstract
Brown’s peony, Paeonia brownii (Paeoniaceae), is one of only two peony species native to the Western Hemisphere, yet its pollination ecology and breeding system have never been documented. Using flowering individuals of an endemic colony in the Blue Mountains of Oregon, U.S., we investigated the peony’s pollination system and floral function. We also examined pollen/carpel interactions through experimental pollinations aided by fluorescence microscopy. Paeonia brownii appears to be self compatible and mostly protogynous with floral traits of a generalist pollination system. The flowers appear to attract insects by producing abundant floral nectar secreted from lobes of a perigynous disc throughout their 9-15-days of anthesis. The most common pollen vectors were wasp queens (Vespidae), the large flower fly Criorhina caudata (Syrphidae), and females of Lasioglossum spp. (Halictidae), all of which foraged exclusively for nectar. Whether collected from foraging wasps and flies, anthers, or stigmas, about half the pollen grains appeared fertile. The number of ovules per carpel was about 19. Seed set (seeds/ovule) of naturally pollinated flowers was about 20% with about 4 viable seeds per follicle. The number of fertile pollen grains transferred to the stigma under natural conditions was highly variable but generally low, which may have contributed in part to the low rate of seed set. This study raises further questions about the role of pollen sterility, floral nectar and vespid wasps in shaping a pollinator system that is unusual in Paeonia.
Highlights
Paeonia brownii shares similar morphology and floral traits with P. californica (Stern 1946); P. brownii is Despite a long history of breeding and propagation that continues today, most wild populations of Eurasian species of the genus Paeonia are listed as threatened or under protection
We identified insects representing 16 different taxa in the Orders of Diptera and Hymenoptera that were collected on open flowers of P. brownii from 2003-2005 (Tab. 1)
During the male phase the flowers produce abundant pollen, unlike the Eurasian peonies they do not attract the assemblage of pollen-foraging bee and beetle visitors, as do, for example, the flowers of P. broteroi, P. jishanensis, P. suffruticosis and P. officinalis (Luo et al.1998; Sánchez-Lafuente et al 1999; Zhou et al 1999; Andrieu et al 2007) or even of its closest congener P. californica (Schlising 1976)
Summary
Paeonia brownii shares similar morphology and floral traits with P. californica (Stern 1946); P. brownii is Despite a long history of breeding and propagation that continues today, most wild populations of Eurasian species of the genus Paeonia are listed as threatened or under protection. Because of their enduring popularity as ornamental and medicinal plants, continual wild collection and habitat loss threaten the existence of endemic populations (Page 2005).
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