Oaks of Missouri

A Guide to the Various Oaks Growing in Missouri

 

 

Introduction

Oaks are unique in many ways, but most strikingly is how well they fit into the stereotype of an “average” tree. Most everyone has had an experience with Oaks, be that collecting the acorns that litter the ground or climbing on their large branches. Oaks tend to be large, with the largest growing up to 100 feet high. They are deciduous trees, meaning not only are they prime for climbing, their leaves turn bright colors and drop come fall. On top of this, oaks account for the highest lumber production of any hardwood tree, being beaten out only by three other species of conifers (softwoods)[1].

 

 

Biology 

Oaks belong to the genus Quercus and there are two distinct groups within the genus: White Oaks and Red (or black) Oaks. Both types of trees reproduce the same way. Oaks are hermaphroditic, meaning have both male and female flowers on the same tree, and pollination occurs by wind. The fruit of the tree, acorns, can take up to two years to reach maturity. Acorns are a staple in the diet of many wildlife, and therefore acorns will only occasionally have the opportunity to spawn a new tree. Additionally, Oaks hybridize with ease, meaning that one species of oak can cross pollinate with another, and grow an entirely new type of tree. Unlike most hybrids, oak hybrids are “viable”, and can reproduce on their own. Because of this, identification of oak trees is much less straightforward than for other genuses. 

Similarities aside, there are a couple of distinguishing features between these two types of Oaks. These differences are apparent in the leaves, acorns, bark, and even the wood of the tree.

  • White Oaks have lobed leaves that are not serrated, while Red (or black) Oaks have bristle-tipped leaves. This is the most distinct feature between the two families of trees.
  • The bark of White Oaks tends to be lighter in color while the bark of Red Oaks varies from a dark grey to brown.
  • For a significantly harder to see distinction: the acorns of White Oaks reach maturity after one year, while those of Red Oaks reach maturity after two years. Additionally, the acorns of Red Oaks have hairs on the insides of their shells, while White Oak acorns do not.
  • Lastly, the timber of the Oak varies greatly between Red and White Oaks. The Red Oak wood is quite pourus and has a reddish tinge while White Oak is leakproof and has a lighter look to it.

 

 

 

 

Identification

Leaves

When identifying oaks, it is important to determine which family the oak belongs in first. This step is generally the easiest, as a quick glance at the leaves. Below are two pictures of the most widely-recognizable oaks from each family. A Pin Oak (Quercus palustris) and a White Oak (Quercus alba). 

 

Photo Courtesy Arborday.org

 

Pictured above is the Pin Oak. Its leaves have deep nodes and come to bristled points at the end of each lobe.

 

Photo Courtesy of Ohio Division of Forestry

 

Above is the other type of oak, a White Oak. The smooth, rounded lobes of the leaves provide stark contrast to the sharp-tiped leaves of the pin Oak. Although not important when distinguishing Red Oaks from White, the "middle" lobes of the White Oak are its largest and help distinguish it from other White Oaks.

 

Bark

Come end of fall and winter, oaks will drop their leaves. While the lack of leaves is definitely inconvient when it comes to oak indentification, it is by no means impossible. By looking at the bark, it is easy to indentify which family the tree belongs to, and often the specific species of tree. 

 

White Oak Bark

The bark of White Oaks is typically quite ridged and furrowed. Which means, in other terms, it is not very smooth. The bark, as aforementioned, tends to be a lighter grey.

Photo Courtesy of Dreamstime

 

Pictured above is the bark of a Swamp White Oak. The ridges and furrows of this particular oak are extremely pronounced which leads to easy identification.

 

Red Oak Bark 

The bark of Red Oaks is much smoother than their White Oak counterpart. The bark is also a much darker color than the bark of White Oaks. In fact, that is where the alternate name for Red Oak comes from: Black Oak. Additionally, a small, but noticeable feature of Red Oak bark is the red tinge in between the ridges in the bark.

 

Photo Courtesy of Ohio Department of Natural Resources

 

Above is a picture of one of the most common Oak's bark: the Pin Oak. Comparing the bark of this tree to the bark of the Swamp White Oak, the differences are quite obvious. The Pin Oak's bark is much smoother and the tinges of red are quite visible within the ridges in the tree.  

 

Entire (unlobed) Red Oaks

Weirdest of all, are the oaks whose leaves are entire, meaning their leaves have none of the lobes so characteristic of the oak tree. There are three of these types of oaks found in Missouri, only one of which is found in more than 10 counties. The three oaks (starting with most common) are: Shingle Oak, Willow Oak, and Water Oak. These oaks, while Red Oaks through and through, deserve their own identification section, as their leaves are tell-tale giveaways when it comes to identifying which oak is which.

 

Below are the leaves of the three trees.

Shingle Oak

Photo Courtesy of Morton Arboretum

 

Willow Oak

Photo Courtesy of Auburn University

 

Water Oak

 

The leaves of these oaks are wildly different than those of the other oaks. Due to their uniqueness, "entire" oaks should be easily identified against other oaks.

 

Reproduction

While there are many aesthetic differences when it comes to oaks, what remains the same for all species is their method of reproduction. As stated before, oaks are hermaphroditic. This means that they can reproduce asexually through self pollination, or reproduce sexually through pollination from another tree. Pollination occurs by wind, and the male flowers produce large amounts of pollen for a period of up to two weeks. Male flowers are easily identifiable; they hang down from large tube-like bodies called catkins, waiting for the wind to carry their pollen away [blog citation]. Lucky pollen, after traveling through the air, find a female flower and attaches itself, thus beginning the production of an acorn. Female flowers are much harder to see, and they often occur where a bud might. Acorns are the fruit of the oak tree, and their journey to becoming a new tree is a harrowing one. Most acorns will not produce a tree, or even have a chance to germinate, as they are a popular meal in the animal community. Acorns are eaten in droves by anything from woodpeckers, to deer.  Pictured below are the male flowers of a Nothern Red Oak.

 

Photo Courtesy of Illinois Wildflowers

 

The topic of oak reproduction inevitably leads to acorns. Oak trees are the only family of trees that produce acorns. While acorns will vary from species to species, they are all generally similar when it comes to the part of an acorn. Knowing the different parts of an acorn can help an eager oak tree indentifier notice certain characteristics, leading to a tree indentification!

 

In the picture below, the basic parts of an acorn are shown. The variation in these parts can  help to distinguish the type of oak the acorn belongs to.

 

The length and size of the actual nut as well as the amount of the nut that the cup covers are the two most common ways to distinguish an acorn.