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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

Variation in Quercus humboldtii Acorns

On a recent trip to Bogotá, Colombia I was able to collect acorns from several Quercus humboldtii growing as street trees on Carrera 70 near the Botanical Garden, and in the nearby Parque Metropolitano Simón Bolívar. I was struck by the different shapes of acorns and cupules I found, not between fruit from a single tree, which were reasonably uniform, but between those from different trees. Some were oblong, some almost spherical, some with a wide flat base, some with a small rounded base. In some the remains of the style formed a small sharp point, in others a thick nipple, and in others it was almost indented. The cupules were all velvety to the touch, but some had a circumference larger than the acorn, while others were the same size, so that the lower scales did not protrude at all from the oval outline of the acorn.

Quercus humboldti acorns collected from
nine different street trees in Bogotá, Colombia

Had I not read that only one species of oak grows in Colombia and has been planted in Bogotá, I would have thought that I was gathering acorns from four or five different species. It is not surprising several other oak species were described in Colombia, namely:

  • Quercus almaguerensis Bonpl.
  • Quercus tolimensis Bonpl. 
  • Quercus humboldtii Kotschy ex A.DC.
  • Quercus lindenii A.DC.
  • Quercus humboldtii var. lehmanniana Hieron. ex Trel.
  • Erytrobalanus duqueana Schwartz
  • Quercus boyacensis Cuatrec.
  • Quercus colombiana Cuatrec.

All of the above are now considered synonyms of Quercus humboldtii Bonpl., named by Aimé Bonpland in honor of his travel companion Alexander von Humboldt and published in Plantae Aequinoctiales in 1809. But two of the synonyms were described by the same author in the same publication! Could these different acorns I found in fact belong to different species? I came across a paper by M.T. Pulido, J. Cavelier, and S.P. Cortés that studied the herbarium specimens of the various names and concluded that they all belong to one species:

The current dataset evidences that the morphological variability observed in leaves and fruits of Colombian oak is continuous. It reflects the presence of only one single species of oak in this country [Colombia] – Quercus humboldtii. Current molecular data support this hypothesis. However, more detailed molecular analysis should be done in order to draw firmer conclusions.

So it seems that the lumpers are clearly in control in Colombia. But is a "Return of the Splitters" called for? Coincidentally, at the same time as I was mulling over these morphological differences, Paco Garín posted on Facebook similar musings, based on Q. humboldtii seed he had received from a commercial supplier, quite different to what he had received in the past from Colombia and grown at Iturraran Botanic Gardens... Quercus humboldtii is listed as under threat due to habitat loss by the Bogotá Botanical Garden (not yet assessed by the IUCN Red List). If these synonyms were restored to species status they would probably be considered endangered at a more critical level. Worth taking another look?

Acorns with wide cupules
Acorns with slim, tight-fitting cupules

Photos © Roderick Cameron