Tuesday, October 21, 2014

Quercus robur or petraea?

For a long time I was under the delusion that there was only one species of temperate, Western European oak:  Quercus robur.

I was wrong.

Quercus robur is the oak of the deep, rich soils and protected coves of Western Europe...the cozy Western Europe of Thomas Hardy.  Quecus petraea is the oak of the shallow soil, of windy exposed knobs and of stony, acidic soil.  That would be the western Europe of the Bronte sisters and the Hounds of Baskerville.

===>This essay<=== explains how to determine if an oak specimen is Q. robur, Q. petraea or a nominal hybrid between the two.

Six specimens collected form my property. Roughly sorted, more robur like on bottom-right corner, more petraea like in upper-left corner.
Bottom right specimen: Petiole and auricles suggest pure Q. robur

Top-middle specimen, longish (9% of leaf length) petiole and lack of auricles suggests that this specimen is not pure Q. robur.
The reason I  hedge my bets and say "...not pure Q. robur" is that these specimens were from seeds collected  in Michigan and potential pollen parents also include Q. alba, Q. bicolor, Q. macrocarpa and Q. muhlenburgii as well as Q. petraea from the originating source in Europe.

1 comment:

  1. Robur and petraea seem to form a species complex, like a lot of oaks, to maximize habitat conditions. Google "Hybridization as a mechanism of invasion in oaks"

    It is a fascinating how oaks are so plastic with their genetics and adaptations.

    " Quecus petraea is the oak of the shallow soil, of windy exposed knobs and of stony, acidic soil."

    Your characterization of petraea above suggests it is the poor hill cousin to robur.



    The reality is it is capable as any oak as these links shows.

    Robur oak is fairly common in North America now but petraea is not. I can't understand why that is since both occur together. Why single one out over the other? Supposedly, the French brought robur here 250 years ago. There is no petraea here and why would they not bring chestnuts that were more useful to them?

    I prefer the look of the petraea leave myself.