Siskiyou Mountains Exploration: Possible Quercus sadleriana Intersectional Hybrids

Dirk Giseburt, Sean Hogan, and Al Keuter

Published May 2025 in International Oaks No. 36: 29–48

Abstract

Quercus sadleriana, restricted in range to the Siskiyou Mountains of southern Oregon and northern California, is the lone North American representative of the disjunct section Ponticae of subgenus Quercus. Recent discoveries by Sean Hogan of possible hybrid individuals between Q. sadleriana and Q. garryana var. breweri (section Quercus) and also Q. vacciniifolia (section Protobalanus) suggest that intersectional hybridizing for these taxa is not impossible today. While awaiting genetic investigation of these individuals, we conducted and report a morphological comparison that tends to support the hybrid hypothesis, in each case with the possible hybrid individual showing some characters that are intermediate between the two possible parent taxa as well as characters in common with each possible parent but not the other. For the possible hybrid Q. sadleriana × garryana var. breweri, the observations are aligned with vouchers collected by leading California and Oregon botanists 40-50 years ago. For the possible hybrid Q. sadleriana × vacciniifolia (see cover photo), the discovery does not have a precedent known to us, and our field observations of at least two possible hybrid individuals – and the progeny of Sean Hogan’s original find – suggest there is an actively reproductive hybrid population of uncertain scope and character that merits further study.

Keywords

introgression, intersectional, breweri, vacciniifolia

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