Horticultural characterization of wild hydrangea quercifolia seedlings collected throughout the species native range

Andrew Sherwood, Lisa W. Alexander, Matthew D. Clark, Steve McNamara, Stan C. Hokanson

Research output: Contribution to journalArticlepeer-review

3 Scopus citations


Oakleaf hydrangea (Hydrangea quercifolia Bartr.) is an understory shrub native to the southeastern United States. Hydrangeas are popular ornamental landscape plants; however, little is known about the diversity in horticulturally important traits for oakleaf hydrangea. Information regarding the variation in important traits could guide future breeding efforts for the species. Seed was collected from 55 populations throughout the range of the species for the purpose of conducting a horticultural characterization of the species compared with select cultivars. Plant architecture was characterized as plant height, number of nodes, internode length, number of branches, and plant width. Plant architecture was measured for container-grown and field-grown plants in two locations (Minnesota and Tennessee). Tolerance to leaf spot (Xanthomonas campestris L.) was characterized for wild-collected seedlings and cultivars by measuring disease severity under exposure to ambient inoculum. Cold hardiness was characterized during two winters with a controlled freezing experiment. During the first winter, seedlings were tested in January; during the second winter, seedlings and cultivars were tested monthly from October through April. Plant architecture varied by environment, with plants growing larger in Tennessee than in Minnesota. The heights of container-grown and field-grown plants were correlated with the collection site latitude (r = 20.66), with populations from the northeastern extent of the range of the species being the most compact, and populations from Florida being the tallest. Leaf spot severity varied significantly among populations and cultivars and was also correlated with latitude for the seedlings (r = 0.70). Two populations in Florida were identified as sources of high tolerance to leaf spot, whereas ‘Flemygea’ and ‘Alice’ were identified as having moderate tolerance to leaf spot. Cold hardiness varied among populations and cultivars and among months of the winter. The overall maximum cold hardiness was observed in February [mean lethal temperature (LT50) = 233.7oC], and several populations maintained an extreme level of cold hardiness into late winter. Midwinter cold hardiness also varied by latitude (r = 20.65), with northern populations showing higher levels of cold hardiness. These results indicate that certain wild oakleaf hydrangea populations will be useful for introgressing novel variation into breeding programs.

Original languageEnglish (US)
Pages (from-to)1023-1033
Number of pages11
Issue number6
StatePublished - Sep 1 2021

Bibliographical note

Funding Information:
Received for publication 2 Apr. 2021. Accepted for publication 23 May 2021. Published online 16 August 2021. Funding was received from the USDA-NPGS Germplasm Exploration and Collection Grant and the USDA-NPGS Germplasm Characterization Grant. S.C.H. is the corresponding author. E-mail: hokan017@umn.edu. This is an open access article distributed under the CC BY-NC-ND license (https://creativecommons. org/licenses/by-nc-nd/4.0/).

Publisher Copyright:
© 2021 American Society for Horticultural Science. All rights reserved.


  • Cold hardiness
  • Disease resistance
  • Germplasm characterization
  • Oak leaf hydrangea
  • Plant architecture


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