Allopatric hybridization and introgression between Juniperus scopulorum Sarg. and Juniperus blancoi Martínez in northern Mexico: Unidirectional gene flow

Analyses of nrDNA (ITS) and petN-psbM (cpDNA) confirmed that allopatric hybridization and introgression are occurring between J. scopulorum and J. blancoi in northern Mexico. Hybrids (by ITS data) all have J. blancoi var. mucronata as the maternal parent and J. scopulorum as the paternal (pollen donor) parent in Sonora and Chihuahua, with two backcrossed plants in the Guadalupe Mtns., TX and two hybrids discovered in northeastern Arizona. No hybrids or introgressants were found that contained the J. blancoi type chloroplast, suggesting the gene flow is unidirectional, north to south, from J. scopulorum to J. blancoi. Prevailing winds (Jan, Feb, March) give support to northern pollen flow hypothesis. Isolated occurrences of hybrids in northern Arizona seem more likely to be products of Pleistocene sympatry, and not modern northern pollen flow from J. blancoi in Mexico to northern Arizona because no J. blancoi chloroplasts (i.e., ex pollen) were found in the USA. It appears that J. b. var. mucronata is in the midst of a chloroplast capture event. Published on-line www.phytologia.org Phytologia 102(1): 14-26 (March 22, 2020). ISSN 030319430.