Biology and Health Sciences


Limoncillo or Runyon's Esenbeckia


In April of 1929, Mr. Harvey Stiles discovered several trees on the bank of the Resaca del Rancho Viejo in Cameron Co. that he did not recognize.  He made a herbarium specimen with fruit and gave it to a well-known photographer and local botanist Mr. Robert Runyon.  Runyon made some more collections from the trees with flowers and sent the specimens to the U.S. National Museum in Washington, D.C. where C.V. Morton determined that they were of a species not known to science.  Morton determined that this was a new species of a genus Esenbeckia in the Citrus Family (Rutaceae). This was the first known occurrence of this genus in the United States and proved to be the northernmost species of this genus of primarily rainforest trees.  For a while, the species was believed to be the same as another species found in the Yucatan area of Mexico "Jopoy",  Esenbeckia berlanderi, but more recent studies confirmed that Morton was correct and that it is a distinct species and the name Esenbeckia runyonii was brought back in use.

Esenbeckia runyonii is only one of dozens of species and varieties of plants that were named after Robert Runyon. Runyon was instrumental in saving one of the last remaining patches of the native Sabal Palm Forest in South Texas. Some of this is now preserved as the Sabal Palm Audubon Center & Sanctuary. Only four populations of the tree were ever known in Texas and like most of our native habitat in South Texas, that land was cleared for agricultural uses.  Runyon planted a tree in his yard in Brownsville which still stands today and was believed to be the last remaining tree in Texas. The tree turned out to be much more abundant in Mexico and populations are known from the states of Tamaulipas, Nuevo Leon, San Luis Potosi, Queretaro and Hidalgo.


In 1984, Don and Mike Heep found an unknown population of Esenbeckia runyonii along one of the resacas in Cameron Co.  Only about 15 trees exist, but a plant that had been believed to be extinct in the wild in Texas had been rediscovered.  This land is protected as part of the Lower Rio Grande Valley National Wildlife Refuge.  Mike Heep runs Heep's Nursery in Edinburgh, Texas and has been growing these trees and using them in landscapes in the Valley area. The Biology Department was able to obtain our seedling and other unique South Texas plants from Heep's Nursery.

Endangered Species?

Obviously Esenbeckia is extremely rare in Texas and is probably the rarest tree in the state, but is it endangered?

Not according to federal law.

The Native Plant Project Endangered Species Committee proposed to the USF&W Service in 1994 to name Esenbeckia runyonii as a federally listed Endangered Species, but this petition was rejected in June 1999 (the file to the petition s990629 is no longer available online at The primary reason was the difference in how plants and animals are treated by the Endangered Species law. A plant or invertebrate must be endangered throughout its ENTIRE range, while vertebrate animals need only be endangered in the United States populations. Limoncillo, as Esenbeckia runyonii is known in Mexico, is an uncommon tree, but was not shown by the petitioners to be endangered in Mexico.


Limoncillo is found most commonly on rocky slopes in moist canyons in the mountains of  Mexico. Chris Best, a biologist with the U.S. Fish and Wildlife service has seen these trees up to 60 ft tall in Mexico but the usual height is about 30-35 ft tall.  In Mexico the tree is sought out by ranchers as a source of "living fence posts".  Branches are cut when the tree is dormant and used as posts for barbed wire fences. When good growing conditions return, Limoncillo will often sprout roots and leaves and begin growing again. Unlike a "dead" fence post, termites and fungus will not destroy a living plant and the rancher has saved himself the trouble of replacing fence posts every few years. Other species in the genus are important timber trees in the Central and South American rainforests.


Limoncillo has glossy tropical-looking foliage and blooms with masses of small white flowers several times a year.  The leaves, 3-8 inches long are composed of three leaflets (trifoliate) which may be 2-5 inches long each. The flowers are small (less than 0.5 in across), white and are borne in dense clusters (panicles) at the end of branches in the summer and sometimes late autumn.  Unlike its juicy fruited relatives the citrus, the fruit is a 5 lobed capsule, that twists and pops out the winged seeds great distances when it drys. The bark of the tree is described as particularly attractive, being gray to black, smooth and peeling like a Sycamore tree.

References and Sources

Much of the information on this page came from personal conversations with:
Mike Heef, Heef's Nursery, Edinburg, Texas
Chris Best, US Fish and Wildlife, Laguna Atascosa Nat. Wildlife Refuge, Rio Hondo, Texas
Joe Ideker, Native Plant Project, Edinburg, Texas

Published References:
Correll, D.S. and M.C. Johnston 1979. Manual of the Vascular Plants of Texas, Renner: Texas Research Foundation.

Department of the Interior, Fish and Wildlife Service. 1999. Endangered and Threatened Wildlife and Plants: 90-day finding for a petition to list the plant "Esenbeckia runyonii" (Limoncillo) as Endangered. Federal Register 64:34755-34756.

Heep, M. and R.I. Lonard. 1986. Esenbeckia berlandieri (Rutaceae) rediscovered in
     southern Texas. Southwestern Naturalist 31: 259-260.

Ideker, J. 1992. Esenbeckia runyonii, Texas' rarest native tree. The Sabal 9:3-4

Morton, C.V. 1930. A new species of Esenbeckia from Texas. J.Wash. Acad. Sci. 20: 135-136.

Simson, B.J. 1999. A field guide to Texas trees. Houston, Texas: Gulf Publishing Company.

Vines, R.A. 1960. Trees, shrubs and woody vines of the southwest. Austin: University of Texas Press.