Rare Woody Plants of Ontario

maple leaves

The Arboretum was one of the first institutions to establish a living gene bank dedicated to archiving known populations of rare woody plants native to Ontario.

Arboretum Gene Banks

The Arboretum established the gene banks as a living archive containing the genetic diversity of many rare Ontario species. These gene banks grew from the long-term vision outlined in The Arboretum’s first (1970) master plan, that recognized the impact of urbanization and non-native species on southern Ontario forests. In 1979, The Arboretum launched its Rare Woody Plants of Ontario Program, called Picking up the Pawpaws. The goal was to survey and document the status of rare woody plant species in Ontario and inform landowners of the significance of the plants on their property. Seeds or cuttings were collected from most of the wild populations or individual plants with the goal of establishing an ex-situ conservation stand for each species as a genetic back up in case in-situ conservation efforts did not maintain survival of the remnant populations. Many landowners participated in these conservation efforts, some of whom were not aware of the unusual tree or shrub species growing on their property.

Today over 30 species of rare woody plants are archived in the grounds and gene banks at The Arboretum, across both research plots and formal collection areas as outlined in the Arboretum Masterplan. The gene banks hold a representative amount of the genetic diversity of such rare species as the Cucumber Tree, an endangered species in Canada, to the relatively common Chinquapin Oak (though few may ever see one). These living gene banks aim, in part, to reduce collection pressure of small surviving threatened and endangered wild populations, increasing the ability of those populations to naturally regenerate.

These ex-situ conservation gene banks represent decades of effort, time, financial and intellectual contributions made by Arboretum staff as well as many community members and private landowners. Detailed provenance data is stored in The Arboretum’s plant records database (IrisBG) and guided by our data management plan.

Research utilizing Arboretum gene bank material takes on several forms, often in a partnership with Arboretum staff and affiliated faculty. Please contact our Research Coordinator for additional information on using the gene banks for research. When planning any projects that might use Arboretum sites or material, please complete our user request forms.

For the Rare Woody Plants of Ontario Program The Arboretum staff visited sites where rare trees had been reported and often find the site bulldozed for agriculture or housing. There have been many cases of rare species loss in southern Ontario. Examples include:
•    A complete loss of a stand of Kentucky coffee trees in Essex county.
•    A soybean field in Lambton county where a stand of pawpaw once grew.
•    A corn field in Kent county where an outstanding, hardy population of flowering dogwood once grew.
•    All but one Chinquapin oak was cut to make way for a housing development in Hastings county.

trees through the seasons

Accessions of known, wild, Ontario-based provenance for selected rare woody taxa under cultivation at The Arboretum University of Guelph.

Last updated in 2023

Taxon Common Name Provincial S-Rank* Total Number of Accessions Total Number of Individuals Provenances Archived (Ontario Counties)
Aesculus glabra var. glabra Ohio Buckeye S1 3 11 Lambton
Amelanchier amabilis Lovely Shadbush S2 / S3 2 3 Essex
Asimina triloba Pawpaw S3 9 10 Essex, Middlesex, Niagara, Kent, Lambton, Elgin
Betula lenta Cherry Birch S1 10 38 Louth Township, Niagara
Campsis radicans Trumpet Creeper S2 3 5 Essex
Carya laciniosa Big Shellbark HIckory S3 6 27 Essex, Elgin, Middlesex
Carya glabra Pignut Hickory S3 3 7 Essex
Castanea dentata American Chestnut S1 2 5 Haldimand-Norfolk
Celtis tenuifolia Dwarf Hackberry S2 5 13 Essex, Hastings, Lambton
Cornus drummondii Rough-leaved Dogwood S4 7 30 Essex. Elgin, Kent
Cornus florida Eastern Flowering Dogwood S2 8 14 Essex, Niagara, Haldimand-Norfolk, Kent
Euonymus atropurpureus Eastern Burning Bush S3 7 29 Essex, Niagara, Waterloo
Fraxinus profunda Pumpkin Ash S1 2 18 Essex
Fraxinus quadrangulata Blue Ash S2 21 49 Essex, Elgin, Middlesex, Lambton
Gleditsia triacanthos Honey-locust S2 10 41 Essex, Kent
Gymnocladus dioicus Kentucky Coffee-tree S2 27 90 Essex, Haldimand-Norfolk, Lambton, Kent
Juglans cinerea Butternut S2 12 32 Lambton, Middlesex, Elgin, Hamilton, Niagara, Waterloo
Liriodendron tulipifera Tulip Tree S4 12 37 Essex, Kent, Elgin, Niagara, Lambton
Magnolia acuminata Cucumber Tree S2 17 37 Niagara, Haldimand-Norfolk
Morus rubra Red Mulberry S2 11 19 Esssex, Niagara, Hamilton
Morella pensylvanica Northern Bayberry S1 1 1 Haldimand-Norfolk
Pinus rigida Pitch Pine S2 3 5 Leeds & Grenville
Platanus occidentalis Sycamore S4 15 26 Essex, Middlesex, Elgin, Halton, Waterloo, Huron
Populus heterophylla Swamp Cottonwood S1 1 1 Lambton
Prunus pumila var. pumila Great Lakes Sand Cherry S3 1 2 Lambton
Ptelea trifoliata Hop-tree S3 19 63 Essex, Elgin, Kent, Niagara
Quercus ellipsoidalis HIll's Oak S3 3 5 Brant
Quercus ilicifolia Bear Oak S1 1 1 Lennox & Addington
Quercus muehlenbergii Chinquapin Oak S4 27 115 Frontenac, Hastings, Prince Edward, Lambton, Essex, Hamilton
Quercus prinoides Dwarf Chinquapin Oak S2 4 13 Leeds & Grenville, Haldimand-Norfolk
Quercus shumardii Shumard Oak S3 5 13 Essex
Rosa setigera Climbing Prairie Rose S2 7 26 Essex, Kent

To learn more 

Fox, Sean. Picking Up the Pawpaws: The Rare Woody Plants of Ontario Program at the University of Guelph Arboretum, 2012, Arnoldia, Volume 69 Number 3.

* ”Conservation status ranks estimate a species’ risk of going extinct or being extirpated. They can also rank a plant community’s risk of elimination. They help identify priorities for inventory, protection and management. … Subnational Rank (SRank) is the conservation status of a species or plant community within a particular province, territory or state…. NHIC assigns subnational ranks (SRanks) for species and plant communities in Ontario using the best available information and considering factors such as abundance, distribution, population trends and threats.” (Natural Heritage Information Centre | ontario.ca)