White Blooming Roadside Trees

This is the time of year that drives native plant folks crazy.  Roadsides and vacant spaces throughout Georgia are displaying upright trees with puffy white blooms.  People sigh and say "Oh, those trees are so pretty."  Before the top of my head explodes, I am compelled to burst out "Those are not native, and they shouldn't be there!"

Pyrus calleryana
James H. Miller, USDA Forest Service
Bugwood.org

People are actually not surprised to find out that those trees are ornamental pears: Pyrus calleryana.  They look just like the ones sold in the store.  But people are surprised to find out how they got there.  The answer is cross-pollination.

Ornamental pears like 'Bradford' are sterile because they are self-incompatible.  This cultivar will not produce fruit by itself.  For many years, people planted 'Bradford' pears and none of them had fruit.  Then the trees began to split and break.  Nurserymen decided to find another tree with a better growth habit.  New cultivars began to appear in the stores: 'Aristocrat' and 'Cleveland Select' (also known as 'Chanticleer') were two of the early ones. When these new cultivars were planted near the old  'Bradford' trees, cross-pollination began to occur.  All the trees which were sterile with their OWN pollen now had a source of compatible pollen and began to produce fruits.

Chuck Bargeron, University of Georgia, Bugwood.org

Birds, especially European starlings, ate some of the fruit and spread it to new areas.  The seeds sprouted and grew.  While the upright form of the parent was passed along to the seedlings, so was another trait that the carefully bred parent didn't have: thorns.  Roadsides and vacant lots became the new home of these thorny invaders, their rapid growth and dense canopy shading out other plants, especially in the southeastern U.S. which shares the same climate as their  native range.




There are many scientific reasons while this plant has become a successful invader - for more in depth details, read the third reference listed below (Culley and Hardiman).  This plant is one of the most noticeable invaders of this decade - an infestation unfolding right in front of us.

Good references for this cross-pollination story include the following:

'Bradford Callery Pear (and other cultivars) Pyrus calleryana ‘Bradford’ ' by Alex Niemiera
'The beginning of a new invasive plant: A history of the ornamental callery pear in the United States' by Theresa Culley and Nicole Hardiman

So if you are thinking about planting this tree, please don't. Research other trees, preferably native, for your area.  And if you have this tree, please consider removing it.  Especially if you notice it setting fruits.

David J. Moorhead, University of Georgia, Bugwood.org

On a positive note, native redbuds (Cercis canadensis) are blooming now.  Their slender branches with tiny purple flowers are peeking out on sunny roadsides, usually from behind something else.  In full sun, they have a more spreading shape.  Their heart-shaped leaves are easily recognized.


P. S. That is not to say that native white trees won't be blooming soon - they will!  I look forward to seeing the blooms of serviceberry (Amelanchier spp.) very soon as well as black cherry (Prunus serotina) and the native plums (also Prunus). But none of those will have the stick-straight silhouette of the ornamental pear volunteers.

Redbud, Cercis canadensis, on the side of the road