Europe. One we were quite familiar with. The other we knew little about. You likely know one of them as English Oak (Quercus robur). Funny thing about common names is they tend to vary from place to place. While many of the English horticulturists we’ve asked call English Oak “Common Oak,” a lot of the Central Europeans call it “Pedunculate Oak.” Because it has no “pins” at the tips of its leaves, has rounded lobes, and the acorns mature/germinate within one year, English Oak is a member of the White Oak group. The other major Oak we find across Europe – and our plant of the month – is Quercus petraea, also known as the Sessile, or Durmast Oak. Quercus petraea is also a member of the White Oak group and is a beautiful tree, capable of reaching over 100 feet tall with age (we’re talking 800 years), but certainly should be considered as a large shade tree for use in the landscape. At first glance, the Sessile Oak looks very similar to an English Oak, but there are some key differences to assist in identifying it. The two common names lead to the ID feature that helps
the most; “Pedunculate Oak – for the English – refers to the long peduncle of the acorn, while “Sessile Oak” refers to the near lack of a peduncle holding the acorn directly on the stem. The reverse is true of the leaves. English Oak has rather short petioles and those of Sessile Oak are about double the length. Another noticeable difference: English Oaks have a more pronounced “auriculate” leaf base, which leads it to it resemble an ear lobe. Now, with Oak wilt being such a concern, it may seem odd that we’re recommending any Oaks for the landscape, but again, there is a time and place for everything, and with proper diversity in our urban landscape, we can be more resistant to all pests. One reason Oak wilt does not impact White Oaks as bad is because they are better at filling up old xylem tissue with “waste” products that block the interconnected tubes that were once used to transport fluids/ nutrients. This blockage makes it more difficult for a fungal infection to move through the tree, thus making White Oak group trees less of a concern – though they are still a concern. continued on page 24 The Growing Concern | May 2019 | 23