Quirky Quercus and the Leaves of its Genus

Old Ironsides was built out of a species of white oak.

Legislation was passed in November, 2004 proclaiming the oak tree the national tree of the United States. I suspect most of us think of oaks as large trees with majestic canopies and easily distinguishable leaves. Probably we think the leaves look like this:

But the number of trees in the oak genus, all of which are members of the Beech family, are reported to be between 400* and 600 worldwide. Michael A. Dirr and Keith S. Warren in their The Tree Book (2019) list the number as 530, including both deciduous and evergreen species. The outdated The Plant List includes at least 605 species and Tree Names lists 605 plants under Quercus.

There seems to be some question as to the number of oak species in North America, too. Many sources suggest there are about 90 species in the US and Canada (Dirr and Warren) while Sibley includes only 69 native species. There are at least nineteen species of oak in California alone. Many sources list the number of  varieties in the US at about 90, but state there are at least 160 species in Mexico. The USDA map for Quercus shows all states except Idaho and all Canadian providences have native or introduced oaks.

On top of the large number of species, the various species easily hybridize, often making classification difficult. Within the two broad classifications of red oak or white oak, though, the trees do not interbreed. Some recognize an intermediate form of Quercus called golden oak. This subgroup may consist of only five species, although other sources state that there are none in North America.

Both red and white oak trees are used for furniture, flooring, cabinets, veneers and paneling. Historically only three species of white oak have been used in cooperage and for aging whiskies and wines.White oak is more often considered for outdoor uses as it has greater rot resistance. Live oak, a type of white oak, was used to build what is currently the oldest commissioned warship in the world, the U.S.S. Constitution. “Old Ironsides” was launched in 1797! Some of the ways to tell the difference between red and white oak trees, as well as their respective lumber, are discussed here.

Acorns give a clue as to whether a tree belongs to the group of red or white oaks, as well as a way to identify the various species. Acorns are also much more variable than I believed as a kid. Some are hairy, others elongated, a few tiny and some huge.

Red Oak with acorn
Note the large size of the cap of the red oak’s acorn.

Unfortunately, we have a lot of squirrels in our park and it is difficult to come across an intact acorn, but if you have an area with an abundance of acorns, this article discusses the foraging and processing of them for use in recipes such as Acorn Mousse and Acorn shortbread cookies. Guidebooks such as Sibley and the National Audubon Society Field Guide to North American Trees will usually include a picture or description of the nut to help with identification. While many species forage for acorns, other animals apparently can be poisoned when ingesting acorns, oak leaves, and bark. Acorns contain tannins and may be bitter. This can be remedied by repeated rinsing of the mashed meal.

Another reason acorns may be hard to come by in our park is the trees may not produce until they are twenty years old and the crop might not be considered a full one until the tree reaches fifty. According to this same source and others, the more bitter the acorn, the longer it will store.

An easy way to tell if an oak is a red or a white is by the leaf. White oak leaves generally have rounded lobes while red oaks have pointy tips. In many cases you have to look very closely as the tip is as thin as a hair.

Red oak tips
Leaves from three species of red oak

With the large number of oak species, it might be of little surprise that not all oak leaves look like you might expect. Some do not resemble that typical sketch above in the least. To complicate matters, the same tree may have leaves of distinctly different shapes! (Sibley, P

There are twenty-six tagged oak trees in City Park, although a number of these are hybrids or varietals. For this first post in a series on Quercus, we look at variations in leaf form. I have ignored the leaves of the hybrids.

Burr, others
The Oregon mountain oak has a small leaf while the burr (or bur) oak has larger leaves with many lobes. The typical leaf might have a more indented mid-section.
English Oaks
All English oaks, which are native to England, are white oaks. This can be seen in these three varieties rounded leaf lobes.
Graves and MOngolian
Note the rounded ends of the Mongolian and Chinkapin Oak, indicating they belong to the white oak group.
Red and Swamp
The swamp oak is a white oak although it is difficult to tell its lobes are rounded. The tips of the northern red oak, though, are decidedly pointed!

The photo below shows the Oriental White oak leaves growing on the tree. I would never have picked out either of these two leaves to belong to the oak family!

 

Although I do not have a photograph, as this tree is not on tree tour, there is a species called the Maple-leaf Oak. This endangered tree currently numbers only about 600. According to Sibley this oak is related to the Shumard, although the pictures of the leaves look  more similar to maple leaves than the skinny Shumard leaf pictured below.

Shumard and Gambel
Shumard Oak (Quercus shumardii) a red oak on the left with its acorn and a Gambel Oak (Quercus gambelii) on the right.

*The Sibley Guide to Trees, David Sibley, 2009

 

 

 

 

 

 

 

 

Catalpa—the Fish Bait Tree

Some consider the long seed pods and large leaves of this tree to be messy

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Flower from a Northern Catalpa

The genus Catalpa contains ten or eleven (North American Trees, 5th Edition) different species of trees. The Chinese variety, Catalpa ovata, which is on the City Park tree tour, is a native of China but has been introduced in the eastern part of North America.

Two species are native to this continent, Catalpa Speciosa and the southern version, Catalpa bignonioides Walt. Even though neither of the other species is tagged in the park, I am going to discuss them because catalpas are one of my favorites. The trees look very similar with their large leaves and long bean-like seed pods. Each also has clusters of flowers, with the native trees blooming earlier with larger blossoms than the Chinese variety.

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Developing leaf of the catalpa.

The Northern Catalpa (C. speciosa) is native to all but eight western states and Florida and has been introduced into Ontario. The Northern Catalpa is the largest of the three trees, normally growing to 60′. The National Champion tree in Indiana is 78′ and  with a 81′ crown spread. C. bignonioides, the southern catalpa, has a range which overlaps that of the northern. It can be found in most of the states where the larger tree doesn’t grow as well as in North Dakota. Although the Southern catalpa is normally only 30-40′ in height (The Tree Book, Dirr and Warren, 2019) the champion tree listed in 2017 is not much smaller than its northern counterpart (75′ x 82′).

The moniker fish-bait tree technically applies to the southern variety of this tree, but the catalpa doesn’t want for other names. They include the cigar-tree, Catawba, Indian-bean tree, caterpillar tree, and Western Catalpa, with the Northern and Southern species sometimes sharing the same alternate name.

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The developing leaves of the Chinese Catalpa with a few of the seed pods from last year

The wood of the northern tree has been used as railroad ties, trim carpentry, telephone poles, fences, and furniture. The southern catalpa wood has been used for similar purposes, but its most interesting use is in plantations where it is grown to attract the the catalpa sphinx moth, which is used for fish bait! (The Tree Book, Dirr and Warren, 2019).

Bark from C. Bignonioides has been used to treat malaria. Other parts of the plant have been used for medical reasons, including the roots, although the current writeup from the USDA includes a warning in red that the roots of this plant are poisonous!  Plants for the Future rates only the Chinese Catalpa as having possible edibility. The USDA does warn that the native trees may be invasive and weedy. Many people complain that the seed pods are messy and many don’t like the large leaves. My feeling is that the larger leaves make them easier to pick up! Even the New York Times took up the case of the catalpa with the story of its spread in the 19th century.

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Bark of the Chinese catalpa

The Chinese Catalpa is smaller than the native trees. An  additional use of its wood is in the making of a traditional Chinese instrument, the Qin.

The Chinese catalpa C 175 in the City Park Arboretum is along Sheldon Drive, just south of the Indian Magic Crabapple on the eastern side of the road, catty corner from the latrine on the west side of the road. The catalpa trees in town seem to leaf out and flower late in the season, so much so that if you own one, you start to worry it has died, yet the Chinese catalpa is even later. It looks quite scraggly even this late in June this year.

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The Chinese catalpa in mid June