Toothache Tree (Zanthoxylum clava-herculis) and Giant Swallowtail (Papilio cresphontes)

Over the past several years, the number of individual toothache trees in the arboretum has steadily increased. The mature tree at the southwest corner of Mickle Hall continues to produce an abundance of fruit, and little volunteers continue to pop up each year. We have allowed the young trees to continue growing, even in locations that are unsuitable in the long-term. For instance, despite there being no future in the aboretum for a volunteer growing next to the trunk of a large mature tree, their leaves can provide food for a very interesting caterpillar. 

Giant swallowtail (Papilio cresphontes) caterpillars have recently been spotted nibbling away on the leaves of a 4-year-old toothache tree (Zanthoxylum clava-herculis). Two caterpillars are captured in this photo. Do you see them?

Here we have another caterpillar, stuck to the spiny, slender trunk of the toothache tree.

They are funny looking creatures. You may even find their heterogenous and mottled appearance disgusting. They are camouflaged to resemble bird droppings! What wonderful diversity occurs in the natural world. And these critters are certainly thorough in their work of stripping the toothache tree of its foliage.

Rather than allowing the horde of caterpillars to defoliate a single tree, we remove a few individuals and place them on the volunteer toothache trees. As noted above, those trees that haven't been added to the catalogue because, based on their current location, they do not have a future in the arboretum.

We certainly want to make sure the caterpillars are well-fed--they turn into such lovely butterflies! Can you think of a better candidate for the "ugly duckling" of butterflies?

Passionflower in the Arboretum

Every year, Hummingbird Central puts out a map where users can report their first sightings of migratory hummingbirds. Let's play a similar game. Have you seen any Gulf fritillaries (Agraulis vanillae) yet? At the arboretum, we're still waiting on them. This year, the arboretum has two species of passionflower for the caterpillars to enjoy. 

Yellow passionflower (Passiflora lutea) can be found throughout the arboretum. It isn't cultivated in any particular spot and volunteers freely. Sometimes we have to pull it off other plants, and sometimes we allow it to climb and twine. This time of year, its quirky little flowers are on display. In this photo, the passionflower vine is attached to a yaupon holly (Ilex vomitoria).

 Also, this summer, we have something extra special. Maypop!

 

Last year we planted Maypop (Passiflora incarnata), specifically during the spring of 2024. In this post from the autumn of 2023, we made clear our intent to do just that. It grew for a short time, but the Gulf fritillary caterpillars soon devoured all of the leaves, so the vine was not given the opportunity to climb or flower. Surprisingly, the plant wasn't killed by this premature defoliation; it started growing again this spring. And it is thriving! There are plenty of leaves for the caterpillars this year. The vine is attempting to climb an old eastern red cedar trunk.

In late July, we are seeing the peculiar "spaceship" flowers, and still no sign of the Gulf fritillary caterpillars. Perhaps these vines will even produce fruit this year. If you've never had maypop fruit, you've missed out on something special! Yum!

Paw Paw (Asimina triloba)

Approaching the end of July, things are still looking green in the arboretum. Thus far, we have had an unexpectedly wet summer. We're around 8 inches in excess of our expected year-to-date precipitation (approximately 40 actual versus 32 expected) and we've had around 7 inches of rain since June 1st. That's enough to keep the frogs happy! New recruits in the arboretum are particularly thankful, one such specimen is pictured below:

This is a young paw paw (Asimina triloba). The young tree comes to us from the banks of the Missouri River in Nebraska, where it was collected by Mark Anderson. Mr. Anderson successfully germinated numerous seeds for a project on his Texas property and was kind enough to donate five plants to the arboretum. This past winter, we planted three paw paw saplings in the arboretum. One died, and one of the two survivors is shown in the photo. Since it's so easy for the weeds to overrun such a small individual, the regular application of elbow-grease (regular weed-pulling) is necessary, especially with all of the aforementioned summer rain. And after the weeds are removed, a layer of mulch must be added to the ground around the stem to prevent the dirt from drying out too fast.

Persimmon (Diospyros virginiana)

In October 2023, we identified and collected eight persimmon seeds from the Caney Lake district of Kisatchie National Forest in Webster Parish. The seeds were immediately planted in one big pot, and during the spring of 2024, they germinated. Seven seedlings grew vigorously in the same pot for approximately a year. 

This past spring, five of the saplings were planted in the arboretum, and two were set aside and repotted as a backup plan. Now that it's June, four out of the five saplings planted in the arboretum are alive, and one in particular looks great. The overall high germination rate and low mortality of these specimens shows how vigorously our native trees must fight for survival in wild conditions. Pampered and given every opportunity by helping human hands, they succeed easily.

This persimmon sapling grows in full sun toward the top of the grassy slope east of Rotary Hall. It is a year old. The trunk is very slender and wobbles under the weight of the big green leaves. Possums are eagerly awaiting the maturity of this tree, although it will be quite a few marsupial generations before any of them get a taste. Perhaps there's an old possum proverb: "The best time for an arboretum curator to plant a persimmon tree was ten generations ago."

Tulip Poplar (Liriodendron tulipifera)

Our little tulip poplar (Liriodendron tulipifera) is growing up nicely. In 2022, this individual volunteered on the north edge of the arboretum, down slope from mature tulip poplars. The following year it was extracted and relocated to a more suitable spot. 

 

In April 2023, the sapling was photographed against a black umbrella when it was less than 8 inches tall. Given that this species can grow to become one of the largest trees (over 100 feet) in Eastern North America, we have on record some modest beginnings.

                                     

Today, it looks healthy and appears to be living up to the expectation of being a 'fast-grower'. Pictured here in June 2025, we see that our tree has grown significantly. Based on photos from last December, it may have nearly doubled in height. The trunk exhibits a slight lean due to the  shade cast by a nearby swamp dogwood (Cornus foemina), but our tree has successfully outgrown that competition. Additional staking would be a prudent intervention to correct the current lean while the tree is still supple. In another decade it will be big enough to support numerous bees and moths with its leaves and nectar.

 

To see a post on the gorgeous fall colors offered by this specimen, click here. 

Summer Concerns; Irrigation in the Arboretum

Centenary College, "Where the sleepy, silver bayou, / Gleams among the pines...." The Alma Mater says that the campus once had a bayou. What happened to it? There are still a few big pine trees, but much has changed over the past hundred years. 

The growth of modern cities with their necessary infrastructure of concrete streets & sewerage has greatly altered local hydrology. Whereas in the past rains might saturate a richly developed soil, rainwater is now swiftly funneled across impermeable barriers of roof-and-road into storm sewers and drainage canals. For our purposes here this means that despite getting on average 50+ inches of rain per year, summer conditions can easily cause drought. Since we need to keep our wide array of arboretum species alive for academic purposes and keep the non-native grass alive for aesthetics, this means we need to supplement our natural precipitation with artificial irrigation, mostly in the form of sprinklers.

An in-ground network of pipes supplies well water to most of the arboretum, and much of that system can be programmed to run automatically. Some lines of irrigation must be manually turned on, and water hoses must be hauled and stretched to reach a few small patches.

The sprinkler system is an absolute necessity for maintaining the health of the arboretum. The fact that it can provide an amusing diversion is a nice side-benefit.

Laurel Cherry (Prunus caroliniana)

Last week on the blog we explained that, even though a tree looks pitiful and nearly dead, we shouldn't rush to cut it down and replace it. This week, we need to explain why a tree that looks beautifully green and productive needs to be cut down and replaced as soon as possible.  

 

A laurel cherry (Prunus caroliniana) is pictured center, completely blending in with its neighbors. On the right side of the frame, we see a non-decaying trunk of a deceased eastern red cedar (Juniperus virginiana) [read more about that individual here].

 

After removing the lower branches, we can now see the trunk of the laurel cherry. It is definitely leaning. 

It's leaning to the south. 

The southward leaning branches were heavy with leaves, and the fruits are numerous. 

Laurel cherry trees are handsome evergreen trees and the fruits ripen to blue. Keep in mind that this species is poisonous.

 

This is an interesting tree, and other than the lean, it appears to be healthy, so why cut it down? There are three reasons. First, the base of the trunk shows damage, which is a serious health concern. Second, there are several laurel cherry trees in the arboretum collection, and there are undocumented volunteers as well, so even if we cut this one tree down, the species will still have a strong presence in the arboretum. Finally, we have a young laurel cherry growing near the base of the trunk, so we can cut the big tree down and allow the young laurel cherry a chance to thrive. For these reasons, this richly green laurel cherry is on the docket for removal. 

 

In this photo, we see that the lower trunk of the laurel cherry is damaged. Also, on the left side of the frame, we can see the young laurel cherry ready to take its place. The young tree has grown up in 100% shade, so if we cut down the older tree all at once, it might be too much of a shock for the little one. So, for today, we started on the gradual process by removing all of the lower branches of the big tree. And in the following months we will steadily remove more branches, slowly exposing the smaller tree to more direct sunlight.

 

 

See previous posts on laurel cherry trees in 2023, and from early 2020 and late 2020.

 

Lady Bird Johnson page on Laurel Cherry 

USDA page on Laurel Cherry