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Plant Focus

Quercus macdougallii
A rare oak endemic to the Sierra Juárez in Oaxaca

Chasing Quercus kelloggii on Santa Cruz Island

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Jonathan W. Long, Richard S. Dodd, John J. Knapp, and Angel Fernandez i Marti

Published May 2019 in International Oaks No. 30: 289–294


Quercus kelloggii (California black oak) hybridizes with some live oaks to form distinctive trees with persistent leaves. One such hybrid, reported as Q. ×morehus (oracle oak), was collected from Santa Cruz Island in the Channel Islands of California, USA, nearly a century ago. This collection was peculiar because neither Q. kelloggii nor the other parent, Q. wislizeni (interior live oak), are known from the Island. In the summer of 2017, a contractor discovered a tree from which a specimen at Rancho Santa Ana may have been collected, as well as two hybrid saplings. Analysis of nuclear and chloroplast DNA microsatellite results suggested the trees are most similar to Q. agrifolia (coast live oak) and Q. parvula var. parvula (Santa Cruz Island oak), which are both common on the Island. This result suggests that the hybrid might be considered Q. ×chasei, (Chase oak) which is a cross between Q. kelloggii and Q. agrifolia, although it appears to be a three-way combination. We consider whether birds or Native Americans may have brought acorns of either the hybrid or Q. kelloggii to the Island, as has been suspected for a number of other plant and wildlife species, or whether long-distance pollenization might explain the hybrid. Resolving the identity of these isolated trees remains a work in progress, due to the complexity of these introgressed populations and the need for additional sampling. The distinctive chloroplast DNA in the hybrid is a reason to conserve and possibly restore the habitat of this isolated remnant of oak diversity.


Quercus agrifolia, Quercus wislizeni, Quercus ×chasei, Quercus parvula var. parvula, oak hybrids, Chase oak, oracle oak, genetics, evolutionary history


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