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Plant Focus

Quercus peninsularis
A Red Oak (Section Lobatae) endemic to inland ranges of northern Baja California, Mexico

A Tough Little Survivor: The West Texas Oak, Quercus hinckleyi

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Janet Rizner Backs

Published May 2016 International Oaks No. 27: 75–82


Quercus hinckleyi C.H. Mull. is listed as a threatened species under the U.S. Endangered Species Act and by the state of Texas and is identified as “Critically Endangered” on the IUCN Red List. It has survived over the past 10,000 years in a region in which the climate has become increasingly xeric. Its U.S. range is now limited to a handful of populations in West Texas. Microsatellites were used to genotype ramets collected from three locations in Presidio County, Texas, that represent all known occurrences of Q. hinckleyi to determine genetic variability, population structure, clonal growth, and levels of introgression by two potential hybridizing species.  Genetic diversity for Q. hinckleyi was high and no evidence of inbreeding was found.   Population structure analyses showed two distinct subpopulations with significant differentiation, unique alleles and genetic clustering. High clonality was discovered at the two smallest sites, with only seven unique genotypes among 58 ramets sampled. Sexual reproduction appears to be present at the other sites, as indicated by less extensive cloning. While there is some hybridization, there was no evidence of genetic swamping. The level of genetic diversity and differentiation among the remaining Q. hinckleyi sites warrants protection and preservation of them all.


threatened species, small plant populations, hybridization, clonal growth


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