A hallmark of the redbud tree (Cercis canadensis) is its ability to produce flowers and fruits on older parts of the tree, including the trunk and main branches.  This phenomenon is termed “cauliflory,” from the Latin, “caulis” (stem) and “flor” (flower), meaning “stem flower.”  In tropical trees, such as cacao and jackfruit, cauliflory is thought to be a reproductive adaptation which allows easier access for pollinators and seed dispersing animals. Flowering along the stem allows heavy fruits to be borne on the stronger lower limbs and trunk.  Cauliflorous flowering in redbud trees is an active area of research and is believed to facilitate pollination and seed dispersal.

Trunk and stem flowering occurs because the redbud tree can produce flowers at the same site on a branch for many years after the initial bloom.  As the tree grows, new flower buds are produced, but dormant buds

remain at the site of the previous year’s bloom. In spring, when the new buds bloom, the older buds can also bloom although they sometimes remain dormant. The combined flowering on old and new wood contributes to the colorful spring display that redbuds are famous for.

Not all redbuds will exhibit this trunk growth. It may occur sporadically or the tree may produce new floral buds on old growth where no buds were previously present. Scientists do not understand all the mechanisms that govern this type of flowering, but environmental and genetic influences are assumed to be involved. The branch of science that studies the cyclical patterns of trees and other living things is “phenology” and there is a national network of scientists and government agencies, The National Phenology Network, dedicated to

gathering data from around the country to help understand how living organisms respond to environmental cues, and how climate change can impact these seasonal changes.  This organization has created the “Redbud Phenology Project” to study redbud trees in different areas of the country.  If you would like more information about this project, including how to get involved as a citizen scientist, visit: https://www.usanpn.org/nn/campaigns/Redbud

Sources:

https://scholarship.richmond.edu/cgi/viewcontent.cgi?article=1130&context=biology-faculty-publications

https://onlinelibrary.wiley.com/doi/full/10.1111/j.1759-6831.2010.00087.x

https://academic.oup.com/aob/article/136/2/309/8159551?guestAccessKey=

https://blogs.k-state.edu/turf/why-is-that-redbud-tree-blooming-along-the-trunk/