Reproductive biology in northern prickly ash

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Zanthoxylum americanum is a common understory species in the northern forests of Minnesota and surrounding regions. It has potential economic importance for its citrus fragrance, pharmacological or insecticidal properties, and produces peppercorns similar to those of the related Zanthoxylum species. Zanthoxylum americanum is a dioecious species but has been reported to have aberrant flowers with autonomous apomixis instead of other potential reproductive barriers. The reproductive biology of Zanthoxylum americanum was investigated in two native Minnesota populations. Determinations of male fertility, whether autonomous apomixis was the predominant floral reproductive mechanism, the presence of seedless fruit (parthenocarpy/stenospermocarpy), and the occurrence of hermaphrodism were made over 2 years. Sex ratios (female:male plants) within each population differed. The mean pollen stainability was 95.8% ± 0.3% (fresh) and 78.6% ± 1.1% (stored 18 months). Parthenocarpy did not occur in either population. Autonomous apomixis was not the primary floral reproductive mechanism. Stenospermocarpy (seedlessness) occurred in 13% of the female fruit clusters. Although commonly described as being dioecious, two additional reproductive strategies were identified: 1) plants with functional protandrous flowers with rudimentary pistils and 2) hermaphroditic flowers with fully functional pistils (protogynous) and anthers. As many as 10% to 30% of the male plants bore at least one fruit/plant each year. One clonal stand had both hermaphroditic and functionally staminate flowers on the same plant. Two evolutionary pathways to dioecy in Z. americanum are proposed.

Original languageEnglish (US)
Pages (from-to)72-83
Number of pages12
JournalJournal of the American Society for Horticultural Science
Issue number1
StatePublished - Jan 2018

Bibliographical note

Funding Information:
Received for publication 13 Oct. 2017. Accepted for publication 29 Dec. 2017. This work was supported, in part, by funding from the Minnesota Agricultural Experiment Station. Special thanks to the Washington County Parks for allowing the study to take place within Cottage Grove Ravine Regional Park and St. Croix Bluffs Regional Park. Many thanks to David Biesboer for review of earlier manuscript drafts. 1Graduate Research Assistant. 2Professor. 3Corresponding author. E-mail:

Publisher Copyright:
© 2018, American Society for Horticultural Science. All rights reserved.


  • Autonomous apomixis
  • Citrus
  • Hermaphrodism
  • Seedlessness
  • Stenospermocarpy


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