Dirr and Warren – What Tree Where

Mystery of the Elms: Chalk bark and others

So many names for the same tree?

On the Fort Collins City Park Self-Guided Tree Tour Map, E23 is listed as the chalk bark Elm. When I googled this, I found very few entries. Instead, a chalk bark maple, the lace bark elm, and references to a Japanese elm popped up. After I got smart and googled the tree’s Latin name, Ulmus propinqua, the Emerald Sunshine elm showed up even though the Latin name for that tree appears to be Ulmus davidiana var. japonica. There is another tree, the David elm, with that very same Latin moniker. What is going on?

The Chalk bark elm near across from Sheldon Lake

The chalkbark elm makes a brief appearance in Dirr and Warren’s The Tree Book,* where part of the mystery of the disappearing elm was cleared up. According to the authors, both GRIN and The Flora of China have regrouped at least four species of Asian elms, considering them to be one species, Ulmus davidiana, or the David elm. Included in this new grouping are what were once known as the chalkbark elm, the David elm, the Japanese elm, and the Wilson elm. Emerald Sunshine, a cultivar, was derived from the chalk bark elm and seems to be discussed under the name U. propinqua JFA-Bieberich. This tree, included in the Tree for Seattle list, is said to grow to a height of 35 feet with a spread of 25 feet and is pest resistant.

To confuse matters, other sources list Ulmus propinqua/Ulmus davidiana var. japonica as the Japanese elm. Another source states Japanese elms include 6 genera and 35 species. According to them, Ulmus davidiana var japonica is the most resistant to Dutch elm disease. Dirr and Warren* state the oldest Japanese elm (Ulmus japonica, now considered U. davidiana var japonica) in the US was planted in 1890 on the campus of UMass Amherst. They also mention this cultivar is known as Discovery “in the trade,” and both Discovery and Emerald Sunshine are listed under the cultivars under the David Elm. I’m not sure if this says we have three of the same tree species in our arboretum or if all three are so closely related they might as well be the same? Most sources also mention Discovery is highly resistant to Dutch Elm Disease.

What does seem to be true is that many cultivars of Asian elms have some defense against the pests that devastated the American elm. Some of the other traits of these trees, such as smaller size or a more upright trunk with less branching, may make them better choices for yards and roadways.

The Siberian elm showing where a recent large branch was lost to a snow storm in April

One type of elm which is usually not recommended is the Siberian Elm (Ulmus pumila.) You can read more about that species on the USDA plant page where it is stated this elm is invasive in New Mexico. It also mentions it is a brittle tree subject to breakage. For a period of time some friends had the National Champion Siberian Elm in their front yard, but a storm about ten years ago broke enough branches it was demoted. With a more recent storm, its size has probably been further diminished. It is possible**, though, that this same tree was still the #2 Siberian elm in the state of Colorado in 2018. The current champion is in the state of Utah.

The Discovery Elm is in the group of trees West of Sheldon Drive and North of Mulberry while one of the two David Elms on the tour is near the entry to the swimming pool. The Chalkbark elm is near the reservable shelter across from the lake and is one of the smaller deciduous trees in that area. The Siberian Elm is not part of the tree tour in the park.

*Diff, Michael A. and Warren, Keith S., The Tree Book: Superior Selections for Landscapes, Streetscapes, and Gardens. Timber Press, 2019

**The champion trees are listed only by city so it is difficult to know for certain if this is the same tree.

The Difficulty of Defining a Fruit Tree, featuring Plums.

A tomato is actually a fruit but legally it is a vegetable!

What exactly is a fruit? My unabridged Random House dictionary has five definitions including: the edible part of a plant developed from a flower; part of plant growth useful to humans or animals; the developed ovary of a seed plant. (Random House Dictionary of the English Language, Unabridged, 1987.) More than likely the average person would say something along the lines of “the part of a plant that we eat” or name a few examples, such as a banana, raspberries, or apples.

Saying a fruit is the part of plants that we eat does not distinguish a fruit from a vegetable, but then some botanists would say there is no such thing as a vegetable. Instead they might identify what we call vegetables as the specific non-fruit part of a plant which we eat, for example, the stem (rhubarb, celery) or leaf (kale, spinach) or root (beets, carrots). The botanical definition of a fruit is simply an organ which contains seeds, but complicating matters is the legal case defining a tomato as a vegetable. Nix vs Hedden was settled in 1893.Yes, a tomato is actually a fruit but legally it is a vegetable!

The purpleleaf plum leaves at their greenest later in the year

All flowering trees (angiosperms) produce fruit, not all of which we eat. According to Gollner, there are between 70,000 to 80,000 plant species which produce edible fruits. Of these, only about twenty species provide the majority of what we consume.* Other sources are even more pessimistic and say the human species relies mostly on TWELVE species of plant.

Excluding citrus trees, nearly all trees producing the common fruits we eat are members of Rosaceae, or the rose family. Genus Prunus includes plums, cherries, apricots, peaches, and almonds, all of which are drupes or stone fruits. Apples and crabapples fall into genus Malus. Their fruits are collectively known as pomes. Pears, in the genus Pyrus, are also pomes. Fruit cultivation probably began somewhere between 6000 to 3000 BCE, primarily in the Fertile Crescent and Eygpt. Some of the earliest domesticated fruits included figs, dates, and olives.

For eons, fruits eaten raw were suspect, with Pliny stating pears were not digestible and Galen suggesting fruits were “troublesome in everyway.”** Early crops looked little like what we now consume. This link provides a few pictures of early fruits.

Prunus is the largest genus in family Rosaceae with the cherries and plums representing the most species. We do have native plums in North America, but information on all the species, often merely labeled “wild plums,” is difficult to come by. Some internet sources allude to many species, but the only place I found multiple species, about 30, enumerated was on a comprehensive map of wild plums throughout the United States. The accompanying blog post explains wild plums are becoming endangered due to the loss of animals (bears) to disperse the seeds.

The list of trees in City Park includes one native American plum (Prunus americana) tree. For nearly a year I have passed by where this tree is said to be located but have not been able to find a tag or determine any definitive characteristics (like evidence of fruit). It either isn’t there or is hidden in plain sight. Most sources list this species as being either a small tree, usually no taller than 25′ or a shrub with prickly twigs. The leaves, like others in this genre are serrated. The bark becomes scaly with age. The white flowers bloom prior to the leaves as early as March. Fruit is 1″ and turns reddish.***

Purple leaf plum was introduced to this county from Asia, is found mostly on the east and west coasts, although older literature shows a swath of the middle of the US as suitable habitat.

There are three purpleleaf plum trees in City Park, Prunus cerasifera Atropurpurea, also known as cherry plum, myrobalan or Pissardii. According to Dirr and Warren, the Atropurpurea variety is from the 1880s and may be the forerunner of many more recent cultivars. Although I have been observing these dark-leafed trees for a number of years, I have not noticed any fruit on them. This could be because, like the American plum, the fruit is only about an inch long. They do have beautiful pinkish white blossoms early in the spring. The foliage changes over the summer from deep purple to a dark green.

The plum trees from their deep purple to later green

To find the purpleleaf plums (C123), walk along City Park Drive from the exit on Jackson Street until you find a cluster of trees in a space encircled with rocks. When they are in bloom, they are easily identifiable by the color of their leaves.

If you want to try and find the American plum, walk along the ditch between Oak Street and Mountain Avenue and see if anything looks similar to a plum.

Dirr, Michael and Warren, Keith. The Tree Book: Superior Selections for Landscapes, Streetscapes, and Gardens, Timber Press, 2019.

*Gollner, Adam Leith. The Fruit Hunters: A story of Nature, Adventure, Commerce and Obsession, Schriber, 2008. p 23

**Ibid. p. 48

***Sibley, David Allen. The Sibley Guide to Trees.Knopf. 2015

Silver Linden. A Bee Killer?

Bees are often found dead or stunned underneath the silver linden.

One of the other unique lindens in the park is the Silver Linden (Tilia tomentosa.} This linden, or lime, is native to countries east of the Adriatic Sea, including Albania, Bulgaria,Croatia,Greece,Hungary, North Macedonia,Montenegro,Romania,Serbia, Slovenia,Turkey, and the Ukraine. The tree was introduced into Great Britain where it grows into north Scotland. This source states the tree was used for lumber in Bulgaria and Romania. Another interesting use of the wood is in carvings found in Orthodox Greek temples.

A paper on various species of linden in the Balkans mentions that Tilia tomentosa tends to reproduce via sprouts. This same paper recounts it is possible for some lime trees to live for a thousand years. It does not indicate which of the various species have reached this age, though. The University of Florida suggests propagation of this species is most often accomplished via cuttings as seed germination can take two years.

Oddly, the USDA calls T. tomentosa a native of Ontario. Most likely this is a mistake as most other sources list it as native to Asia and Western Europe exclusively. In North America this variety is hardy in zones 4-7 and was introduced in 1767.

Monumental Trees lists the tallest silver linden, a tree in Belgium, at 121 feet. The US list of Champion trees has no listing for Tilia tomentosa, although many sources, including Dirr and Warren’s The Tree Book:Superior Selections for Landscapes, Streetscapes, and Gardens, say it is an excellent street tree that is more resistant to aphids than other lindens, although other sources dispute this. This may also be true of Japanese beetles. It may be more drought and pollution resistant.This information seems to differ by the state which provides it and leads me to believe its properties vary with the environment it is in.

Heart-shaped, serrated leaves

Serrated leaves of the silver linden.

With the silvery underside to its leaves, many consider this a good shade tree with a shimmery effect in a breeze. Like most other lindens, bees are very attracted to its flowers from late June into July. Dirr and Warren, as well as others, report this might not be a good tree for bees as they are often found dead or stunned underneath them. Bumblebees are more prone to suffer than honey bees. Recently studies have been done to figure out if the problem lies with the biology of the bees or has to do with the flower nectar. The conclusion reported in a Royal Society (2017) article is that further study is needed to determine the cause of death.

E17 Silver linden specimen Tilia tomentosa in City Park is a smaller tree located along the drive to the golf course parking lot. Part of the fire station can be seen in the background of this photo.

OLYMPUS DIGITAL CAMERA — Tilia tomentosa

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