Tree of the Week: American Chestnut (Castanea dentata) 'Dunstan'

Our tree of the week is an American-Chinese hybrid chestnut tree, Dunstan. You can read the history this individual on a previous blog post, here, and you can learn about the company responsible for the development of Dunstan here. Today, we have a particular complaint to lodge against this specimen that the pubic may find of interest. Our chestnut tree is a litterbug.

The tree of interest is pictured center. It grows at the bottom of a slope between a sidewalk and a drainage channel.

In this last week of May, our chestnut tree freely (and no doubt absent-mindedly) drops its refuse, littering one of our main thoroughfares in the arboretum.

The discarded plant material is a little disturbing, resembling little, fuzzy, tan-colored snakes or large worms. Very strange....

These are the male flower clusters of the chestnut tree.

Chestnut catkin, 8 inches in length

Chestnut catkin, 7 inches in length

Chestnut catkin, 6½ inches in length

Zooming in, we can see the fuzziness.

We would like to say that our chestnut tree has an otherwise clean record, but, unfortunately this is not the case. Nor is it the most egregious of its missteps. As the year winds down the chestnut tree drops large, spiky orbs. During the past two years, the litter problem has been significant.

These spikes are not "all bark and no bite." They are as painful as they look. You might object and think 'but wait! this ball of spines is actually a capsule for tasty snacks.' Let's see about that.

After incurring the inevitable painful stabs, we discover that the hoped for tasty chestnuts are shriveled, small, and inedible! The disappointment is poignant.

Why are the chestnuts wizened? Is there a water, fertilization or pollination problem?

The arboretum's irrigation system keeps Dunstan hydrated during the hot months of summer, so we can cross water-shortage off the list of possible explanations. Inadequate fertilization and pollination are both reasonable explanations for the small fruits. The company responsible for Dunstan, Chestnut Hill Nursery and Orchards, recommends planting at least two Dunstans for proper pollination. We only have one. Also, other than applying mulch around young trees, we tend not to introduce any fertilizers into the arboretum landscape, so Dunstan has not received the recommended fertilizer treatments. If we want our Dunstan to produce delicious chestnuts, we ought to do something different. However, a healthier, more successful tree means even more litter!

Tree of the Week: American Chestnut (Castanea dentata) 'Dunstan'

The no-rain weather continues in Caddo parish. And it's been hot the past few days, too. Around the arboretum, a couple trees are dropping leaves, several trees are turning colors, and a good many trees are dropping fruits, mostly acorns.

Our tree of the week is in a class of its own; its fruits are very interesting. This is 'Dunstan', a hybrid between the American chestnut (Castanea dentata) and the Chinese chestnut (Castanea mollissima). Until the 20th century, the American chestnut was a bedrock species in the uplands of Eastern America. A disease was introduced into the native tree populations, and subsequently the American chestnut went the way of the buffalo; minor populations survive but nothing like the past glory remains.

Ed Leuck acquired Dunstan from Sherwood Akin nursery in Sibley, Louisiana, and it was planted in January 1996, at the bottom of a hill near the stream. In 2005, it was damaged by a falling mockernut hickory (Carya tomentosa), which broke its top. Today it's in good health, growing in a shady spot near the Fitness Center.  

Dunstan is pictured in the center. The on-site native sweet gum (Liquidambar styraciflua) is on the far left. Sweetbay magnolias (Magnolia virginiana) and a basswood (Tilia caroliniana) are in the background. This is a very shady spot.

Behind Dunstan, on the opposite side of the stream, the arboretum's floodplain is located. A red maple (Acer rubrum) is pictured on the far left and an overcup oak (Quercus lyrata) is pictured on the far right of the photo.

The narrow leaves pictured above are characteristic of Castanea dentata, rather than C. mollissima.

In the leaf litter, we can find the fruits. They must be falling from way up top because none could be spotted on the lower branches.

The husk of the fruit is extremely spiny, and it hurts! Thick gloves are recommended.

The wider leaf pictured above resembles the leaves of Castanea mollissima. The delicately serrated leaf margins of Dunstan also resemble the leaves of C. mollissima, rather than the more coarsely toothed leaves of C. dentata.

The underside of the leaf is fuzzy, a characteristic of C. mollissima. The husk of the fruit pictured above is split: get a pair of gloves and pull it apart.

The large prickly husk concealed three small nuts. The interior of the husk is velvety.

Light-grey furrowed bark of a 20-something-year-old tree

Click here for more images of the arboretum's American chestnut hybrid.


For more information about the American and Chinese chestnuts and their Dunstan, please see the following links:
University of Marlyand Extension
Chestnut Hill Nursery and Orchards - creator of Dunstan
Virginia Tech Dendrology - Castanea dentata
Virginia Tech Dendrology - Castanea mollissima

This past Wednesday a lot of rain fell, accompanied by some gusts of wind. A couple large, dead branches were knocked loose and fell to the ground with the rain. Luckily for us, some branchlets fell, too, giving us a look at this year's growth from the tip-top of the old trees. 

White oak (Quercus alba) leaves and acorns

This bristly fruit fell from the hybrid American chestnut tree (Castanea dentata). Ouch! We aren't going to bust it open quite yet.

Water oak (Quercus nigra) acorn and leaves.

The sweetgum (Liquidambar styraciflua) often acquires a bad wrap because of its pointy fruits. There is one large on-site native sweetgum in the arboretum collection, and, admittedly it does make a mess of the sidewalks. It has sustained damage over the years, so this past summer a volunteer sweetgum growing up in the groundsel bush (Baccharis halimifolia), away from foot traffic, was admitted into the catalogue, so that we have a back-up specimen should something happen to the old one.

This image shows the relative size of the different fruits.

The fruit pods of the strawberry bush (Euonymus americanus) are changing color and opening up.

The orange-red seeds of the strawberry bush are revealed. They should not be eaten!

Castanea dentata