IntroductionNorthern Wild Senna (Senna hebecarpa) was once widespread throughout New England, but is now rare and endanger of extinction throughout much of its native range. In New Hampshire, the plant has been classified as endangered and critically imperiled statewide (NH rare plant list 2008). Little is known about the biology of this species, which reproduces asexually via vegetative ramets (clonal stems) and sexually by producing seeds from bee-pollinated inflorescences. Given the plant’s rarity, genets (genetically distinct individuals) are often isolated and prone to self pollination between clonal ramets, which can lead to a loss in fitness due to higher than normal levels of inbreeding (i.e. inbreeding depression).

Reproductive Biology of the Endangered Wildflower Senna hebecarpa I: Pollination and Fecundity

Justin Wheeler, Christopher Darnowski, and Eric Berry

Department of Biology, Saint Anselm College, Manchester, New Hampshire USA

Methods• Study site - Amherst Country Club, Amherst, NH

• Phenology - 17 genets monitored from 15 July to 10 August 2007

• Pollination treatments - 20 genets per treatment in a nested design:

Results

Conclusions• Synchronous flowering within multiple ramets facilitates self pollination, especially among isolated genets

• Reduced fruit set due to inbreeding depression may be limiting the recruitment of new sexually-produced genets into the population

• Management efforts that supplement small populations with additional genets will promote cross pollination and reduce the impact of inbreeding depression.

AcknowledgmentsWe thank Jamin Warren, president of the Amherst Country Club, for permission to study S. hebecarpa on the club’s property. Funding was provided by the SAC Biology department.

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Figure 3. Effect of pollination treatment on fruit set (fruits / flower) and seed set (seeds / fruit) in S. hebecarpa.

Figure 2. Flowering phenology of S. hebecarpa, showing the percentage of ramets flowering in the population (bar) and the average number of receptive flowers per raceme (line).

References• Rare Plant List for New Hampshire. New Hampshire Natural Heritage Bureau. 2008. (http://www.dred.state.nh.us/divisions/forestandlands/bureaus/naturalheritage/index.htm)

Research Objectives• Document flowering and fruiting phenology

• Quantify impact of inbreeding depression on fecundity

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Figure 1. A. Emasculated flower B. Seed pods C. Insect enclosure

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Hand pollinated v. Open pollinatedCross v. Selfed Emasculated v. Control

• Analysis of variance on fruit set and seed set tested using theGeneral Linear Model = hand + selfed (hand) + emasculated (hand)

Results• Wild Senna is not agamospermous; pollinator-excluded flowers produced no fruits

• Flowering (figure 1) and fruiting was highly synchronous. Fruits set by 16 August and ripened through October.

• Self pollination produced a moderate reduction in fruit set (F=3.60,P=0.062), but had no impact of seed set (F=0.45, P=0.505) (Figure 3)