A Pleistocene Clone of Palmer's Oak Persisting in Southern California

BACKGROUND: The distribution of Palmer's oak (Quercus palmeri Engelm.) includes numerous isolated populations that are presumably relicts of a formerly larger range that has contracted due to spreading aridity following the end of the Pleistocene. PRINCIPAL FINDINGS: We investigated a recently discovered disjunct population of Palmer's oak in the Jurupa Mountains of Riverside County, California. Patterns of allozyme polymorphism, morphological homogeneity, widespread fruit abortion, and evidence of fire resprouting all strongly support the hypothesis that the population is a single clone. The size of the clone and estimates of annual growth from multiple populations lead us to conclude that the clone is in excess of 13,000 years old. CONCLUSIONS: The ancient age of the clone implies it originated during the Pleistocene and is a relict of a vanished vegetation community. Range contraction after climate change best explains the modern disjunct distribution of Q. palmeri and perhaps other plants in California

MORE AMERICAN BLACK SAPOTES: NEW DIOSPYROS (EBENACEAE) FOR MEXICO AND CENTRAL AMERICA

Volume: 22Start Page: 277End Page: 30

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Volume: 21Start Page: 2045End Page: 205

THE DIOSPYROS SALICIFOLIA COMPLEX (EBENACEAE) IN MESOAMERICA

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Comparison of mean annual temperature and mean annual precipitation among occurrences of <i>Q. palmeri</i>.

<p>The black dot represents the <i>Q. palmeri</i> at the Jurupa Mountains site. The Jurupa site is outside the one-tailed 95% confidence interval for both variables.</p

Cross-sections of <i>Q. palmeri</i> stems.

<p>Ring counts were made from high-resolution images of cross sections of each stem. Scale is in millimeters. Example stem sections, from left to right: Jurupa Mountains, Aguanga, Garner Valley.</p

Map of the studied population of <i>Q. palmeri</i>.

<p>White dots and ‘X’s represent known occurrences of <i>Q. palmeri</i> throughout California; the red ‘X’ in the insert represents the location of the Jurupa population. Percentiles are the two-tailed probability of suitability given 19 bioclimatic parameters.</p