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Michael Eason hiking in Anza-Borrego Desert State Park to observe Washingtonia filifera in situ
Currently at San Antonio Botanic Garden, Michael's work has...
Amy Byrne | Feb 15, 2023
An exhibition that beautifully depicts and locates oaks
Roderick Cameron | Feb 09, 2023
Burke Oak Collection at New York Botanical Garden
The Coleman and Susan Burke Oak Collection at The New York...
Todd Forrest | Feb 08, 2023

Plant Focus

Quercus xjackiana acorns
The hybrid of Q. alba and Q. bicolor

Mysterious Hansen Name Unveiled

In some oak databases one can find a few oak names described by a certain Hansen. And in every instance there is no link to a publication whatsoever. The most common cases are Q. greeneana, Q. patula, Q. rineharticena and Q. viridis. First I thought I might find something by searching for Swedish or German botanists, but I found nothing, although I was moving in the right direction (see below).

While browsing for Q. garryana Douglas ex Hook. on the invaluable website http://plants.jstor.org, I saw a herbarium specimen named Q. garryana Dougl. [sic],  but with a second label: Q. greeneana Hans. (leg. Georg Hansen). This label led me to a work written by Georg Hansen called the “Flora of the Sequoia Gigantea Region”. In this work Hansen describes some oak specimens: Q. greeneana, Q. patula, Q. ×dubia, Q. rinehartiana (not rineharticena), Q.×viridis, Q. ×morehus nothovar. nobilis and Q. chrysolepis var. mira.


Quercus greeneana, Quercus patula are synonyms of Quercus garryana Douglas ex Hook. var. garryana. Quercus viridis and Quercus ×morehus nothovar. nobilis are synonyms of Quercus morehus Kellog. Quercus

Quercus jacobi R.Br.ter and Q. garryana Douglas ex Hook.

chrysolepis var. mira could well be a synonym of Quercus chrysolepis Liebm. Quercus ×dubia (= Q. keloggii x Q. rhinehartiana) and Quercus rinehartiana are still unresolved. But Hansen wrote about Q. rinehartiana: “Species near to Kelloggii, but distinct in its lanate foliage, shoots and acorns.” Jepson commemorated Hansen in Quercus chrysolepis f. hansenii Jeps., (1909) and in Quercus chrysolepis var. hansenii (Jeps.) Jeps., (1923). A lot of other genera have the specific epithet hansenii.

Keen plantsman

The German born plantsman is also known for his fine drawings in Greene‘s” Illustrations of West American Oaks”. He wrote “The Orchid Hybrids: Enumeration and Classification of All Hybrids of Orchids”, published in 1895. W.L. Jepson wrote about the life and work of this remarkable man in Madroño in an article named THE BOTANICAL EXPLORERS OF CALIFORNIA part III (Madroño, Vol. 1, No. 12 (September, 1928), pp. 183-185).


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Quercus garryana Douglas ex Hook. [as Quercus jacobi R. Br.ter] Quercus gilberti Greene
Quercus macdonaldi Greene Quercus turbinella Greene