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Monday - November 05, 2007

Region: California
Topic: Non-Natives
Title: Cross pollination of orange and crapemyrtle
Answered by: Barbara Medford


I have a crapemyrtle tree growing 3 feet from a navel orange tree. This summer a shoot grew from the ground 5 inches from the orange tree. The shoot looks just like the orange tree but the leaves were identical to the leaves of the crapemyrtle. The shoot produced a small (about the size of a keylime) fuzzy "orange" which ripened in September (oranges are ready in December here). The leaves of the orange tree remain on the tree year round but the leaves of the shoot have dropped off like the crepe myrtle does this time of year. Is it possible for these two trees to cross pollinate?


First of all, the Lady Bird Johnson Wildflower Center is centered on the care, protection and propagation of plants native to North America. While the Malpighia glabra (wild crapemyrtle) is native, it appears naturally only in Texas.

The crapemyrtles distributed commercially and grown in Zones 6 to 9 are all natives of Asia. In recent years, the Japanese crapemyrtle has been becoming more popular in the U.S., extensively hybridized both for variations in color and form, and also in an attempt to limit damage from mildew. Crapemyrtles are members of the family Lythraceae and genus Lagerstroemia.

Orange trees, family Rutaceae and genus Citrus, are native to Vietnam, Southern China and Northwest India. They were brought to the New World early, and in 1820, a single mutation appeared in an orchard of sweet orange in a monastery in Brazil, producing the navel orange.  Because the mutation left the fruit seedless and therefore sterile, the only means available to cultivate more of this variety is to graft cuttings onto other varieties of citrus trees.

So, even though we are talking non-natives, Mr. Smarty Plants couldn't resist possibly being part of the discovery of a whole new plant. Alas, it was not to be. Cross pollination usually only occurs between plants of the same or closely related species (not between Lagerstroemia and Citrus); foreign pollen landing on a receiving blossom is incapable of delivering that pollen. It is believed that a flower obtains clues to the alien pollen's incompatibility from the grain's shape and chemical composition.

So, how about another mutation, you say? Slightly possible, but way out of our line. We are guessing that a bird (birds are great little gardeners) ate a nice seed somewhere maybe miles from your yard. He continued his seed gathering while the seed worked its way through his digestive system. Then, he stopped to perch on your lovely orange tree, and deposited the seed with a little fertilizer added (no charge).

If you would like to know what the plant is that came up, Mr. Smarty Plants loves to identify plants. However, it is very difficult to do from a description. The fuzzy little "keylime" that emerged sounds like a seed pod. If you got some pictures before the leaves dropped off and could send one to us, we might be able to identify it. There are instructions for sending pictures on the lower right hand side of the "Mr. Smarty Plants" page.


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