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Biodiversity Blog


Trees of BFL: the Redbud

Photo collage: Larry Gilbert


Nothing quite signals the coming of spring in Austin like when a redbud tree starts to bloom. After our brief but botanically-drab Austin winters, the bright pink flowers are a welcome and invigorating sight.

At Brackenridge Field Lab, redbuds grow there natively in places where limestone quarries existed in the late 1800s.

They are members of the pea family (Fabaceae). Some websites will explain that the North American redbud Cercis canadensis has three geographic varieties. However, according to George Yatskievych, Curator in the Billie L. Turner Plant Resources Center, the taxonomy of the North American redbud is a bit more complicated. The most recent classification was in 2018, by a group led by Peter Fritsch, the head of research at the Botanical Research Institute in Texas (BRIT) in Fort Worth. This called for the recognition of three species. George explains: "The eastern redbud, Cercis canadensis, whose overall distribution extends through Texas and into eastern Mexico, has a range of leaf morphologies and growth forms that relate to available moisture. Thus, Fritsch does not formally recognize varieties, such as var. texana and var. mexicana, because they are apparently environmentally-based rather than genetic lineages."

In the western United States, there are two species involved that are cryptic, meaning they are difficult to distinguish morphologically, but are distinct genetically. "The oldest name, Cercis occidentalis, is now reserved for plants that are found natively in California," George explains. "Plants in Arizona, Nevada, and Utah, which had also been going under the name C. occidentalis, are classified by Fritsch et al. as a segregate species, C. orbiculata."

red bud
Photo: Nicole Elmer

Difficult taxonomy aside, these trees have some unusual qualities and interesting uses. One of their quirks is what is called "cauliflory," which is the tendency to make flowers through the bark on older branches on on main trunks. Also, the papery fruit walls persist on the trees through the winter into the next growing season. In food uses, the bright pink flowers of these North American trees can actually be eaten. In parts of Appalachia, the green twigs are used to season game like venison and opposum. Some Native American tribes also consume the flowers raw or boiled, and eat the seeds after roasting them.

In general, redbuds don't grow particulary tall, about 15-30 feet, and are short-lived. They often last around 20 years before the trunk splits or branches start to die. Since they are such showy trees, they are common ornamentals. However, the trees you will find at plant nurseries are not always the local genotype

For a bit of culture, according to legend, Judas Iscariot hanged himself on a tree related to the redbud (Cercis siliquastrum), or the Judas tree.

Thanks to George Yatskievych for his edits on the piece.

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