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.

Tree of the Week: Redwood (Sequoia sempervirens)

Officially, the Ed Leuck Louisiana Academic Arboretum is a place for trees and shrubs native to the southeastern United States. From its beginning, one of the primary goals for the arboretum was to plant young trees of the same species that were naturally growing on the college campus. As experimental plantings and for botanical interest, non-native species have been planted in small numbers. One such specimen is featured on the blog today: the redwood (Sequoia sempervirens), a tree native to north America, but certainly not the southeast. At this juncture in history, the redwood naturally grows in northern California, near the coast, and up into Oregon.

During the spring of 1990, Professor Ed Leuck obtained a redwood seedling from Forest Farm Nursery, located in Oregon. It wasn't planted in the ground until January 1996. That means this individual is more than 33 years old.

 

Professor Leuck chose a location on the periphery of the arboretum, in a triangle of grass at the eastern corner of the Student Union Building. The triangle is formed by two sidewalks and the Student Union Building driveway. The redwood is pictured center, partially obscuring the corner of the SUB. It has a straight trunk and it is significantly taller than the building. If you follow the trunk all the way up, you will see why this tree is of special concern this week.

 

The top of the redwood looks dead! What happened here!?! How long has it looked like this? Our forward looking gaze needs to turn upward more often.

The trunk hasn't shown any signs of distress. It's a thick, handsome trunk, growing next to a busy intersection of sidewalks. Typically, there are fresh green shoots near the base of the trunk. Today was no exception.

 

After the shoots were trimmed back, a white string was tied around the trunk, 3½ feet off the ground. At more than 33 years of age, this redwood measures 5 feet around. This species is known for rapid development, so its large size is no surprise.

The bark is reddish-brown, fuzzy, and furrowed. All of the lower limbs have been removed for sidewalk traffic, but upper limbs droop down to showcase pretty green foliage. Can you see a face on the trunk? Several lower branches were trimmed today to clear the sidewalks. The act of trimming branches creates a pleasant aroma in the air; leaves and branches are nicely fragrant, like citrus.

This is a short branch with numerous leaves. Redwood leaves are very small.

Leaves have a feathery appearance but aren't soft. Some of the leaves feel rubbery while others feel pointy.

 

It's summertime, by the way, season of the cicada.

 

Here we have 5 leaves, all narrow and less than an inch in length. All of these leaves were taken from the drooping lower branches. The leaves way up top are alleged to have a slightly different appearance. Of course, the leaves at the top of our redwood look dead!

 

Reading online sources about this species confirms the obvious: this non-native tree is out of its element. This redwood could tolerate the hot July weather if it also had some fog to help it replenish its water loss. For 20 years, this specimen thrived in the shadow of the Student Union Building, a nice micro-climate that helped it retain moisture. Now that the redwood has out-grown its sheltered environment, it is suffering. That's one explanation, at least, for the sudden unhappy appearance. 

The online literature also tells us that all hope is not lost. Redwoods have an amazing ability to re-sprout: if it loses its crown, it can grow another one! For now, we need to make sure this individual gets extra water during our late-July heatwave, and remember to look up more often. 

For information about this very interesting species, consult the following online sources:

U.S. Department of Agriculture, Forest Service, Southern Research Station

National Park Service 

Virginia Tech

Tree of the Week: Arkansas Oak (Quercus arkansana)

 

As we continue our project, Acorn Watch 2022, we are looking at the arboretum's only Arkansas oak (Quercus arkansana). This tree is more than 25 years old. It was collected locally in Caddo Parish. In November 2021, we examined this individual and were happy to find a ripe acorn. At the time, we also found online that, according to the International Union for Conservation of Nature, this species is considered 'Vulnerable'. So, the acorns from the Arkansas oak are of extra special interest.

Looking for acorns can be a challenge. The tree must be old enough to produce acorns, which often means that the tree's lower branches have either been removed or dropped. Luckily, our Arkansas oak has a drooping branch with a couple of acorns. A ladder was used to take the pictures.

 

Here, we see dark green leaves and one immature acorn. The Student Union Building bricks are blurred in the background.

 

On this twig, we see two different cohorts of acorn, both immature. The larger acorn will ripen this year, and the smaller acorn will ripen next year.

 

So, how long will it take the larger ones to ripen? Can we expect ripe acorns in October or November? We shall see!

 

 

Tree Removal: Box Elder Maple (Acer negundo)

 

This week we say goodbye to a box elder maple (Acer negundo). We do not know the age of this tree. It was a volunteer, and when it entered the catalogue, an approximate age was not given.

 

This tree has been tagged for removal since spring 2020, after it suffered significant storm damage. You can read about it and see pictures of the storm damage here. In the above photo, we see a thick, straight trunk and dense foliage up top. It's clearly alive.

Up close and personal, it's truly awful.

Here we see fungal growth, mold, missing bark, and insect damage.

This is extensive, running across half the circumference.

At about four feet up the trunk, the tree had a circumference of 30 inches.

The first step in removal is to take off lower branches.

Then the crown and all the other branches were removed, leaving only the trunk.

The trunk was taken down in one piece.

There was an entire ant civilization living in the caverns of this tree, fifteen feet off the ground. Luckily they could only bite and not sting with venom.

After stump removal, there's not much evidence of this tree's relatively short life. Its memory will be preserved on this blog and our records.

Tree of the Week: Nuttall Oak (Quercus texana)

Our Nuttall oak (Quercus texana syn. Q. nuttallii) has a recorded history of high acorn production. You can read about it on an old blog post, found here. This year, acorn watch 2022, we see, especially by comparison, an exceptionally high number of Nuttall oak acorns. This specimen is especially valuable as germplasm because it is a local genotype.

 

This Nuttall oak grows in a low spot, at the bottom of a gradual slope, near the campus Fitness Center. At four feet off the ground, the thick trunk has a circumference of sixty-two inches. As we can see, all of the lower branches have been removed.

 

 

This tree grows at the conjunction of two sidewalks. Because of its proximity to foot traffic, this Nuttall oak has endured much pruning over the years. The large circle in the center of the trunk is where a large limb was removed.

 

Large, circular scars can be found further up the trunk as well.

 

 

We see smaller circles, too.

 

 

Note the prominent surface roots, reminiscent of live oaks. Keep this one away from important sub-surface infrastructure.

 

 

Note the serpentine curling.

 

These are quite handsome. Don't you think a bonsai enthusiast would enjoy it?

 

 

 

Although mostly obscured by the thick foliage, numerous clusters of developing acorns can be found if you go looking for them. These acorns were photographed without the aid of a ladder―although the lower branches have been removed from the trunk, the upper branches droop down.

 

More cap than corn at this stage.

 

Here we can appreciate the two different sizes of acorns. There are two different sizes because they take nearly two years to develop. The larger acorns will ripen this fall/winter, while the smaller ones will ripen in 2023

 

 

Thankfully for the purposes of our acorn project, two twigs needed to be trimmed from the drooping branches. They incidentally had several acorns attached to them.

 

 

Here we see mostly the larger but still immature acorns. One smaller acorn, on the middle of the bottom row, will ripen in 2023 if it hangs on until then.

 

 

Tree of the Week: Durand Oak (Quercus sinuata)

Continuing our study of the arboretum's acorn production, we have photos below of the Durand oak and its immature acorns. Out there in the bright sunshine, our Durand oak is labeled Quercus durandii, but another widely used binomial is Quercus sinuata.

Our lone Durand oak (Quercus durandii syn. Q. sinuata) is approximately 25 years old. You can read about its acquisition on an older blog post found here.

This week in July, you can find immature acorns on the branches. This isn't the first time that we have seen fruits on this tree. In June of 2019, we posted photos of developing acorns; however, we have yet to examine mature fruits.

 

There are more than a handful of immature fruits that are easily observable from the ground.

 

Immature acorns of Quercus durandii syn. Q. sinuata (July 10, 2022)

 

Immature acorns of Quercus durandii syn. Q. sinuata (July 10, 2022)

 

And, if the sweltering heat and blinding sunrays haven't convinced you that summer has arrived in northwest Louisiana, here we have another sign of the season―a cicada exoskeleton was found firmly attached to our Durand oak.

 

Tree of the Week: Silverbell (Halesia diptera)

Our tree of the week is the silverbell (Halesia diptera). Silverbells were among the first plants included in the arboretum catalogue. Since 1985, there have been 12 individual plantings, 11 of which were donated by local resident Jack Price. Today, only three survive.

 

 

In February of 1985, Jack Price donated five trees. Our three remaining silverbells are from this bunch, which makes them more than 35 years old. They were planted together, in a row, toward the bottom of a slope, near the arboretum drainage channel.

 

 

It just so happens that all three trees have terrible posture. Two of the trees lean heavily toward the south. In 2021, this location receives a fare amount of sun. However, the landscape has changed significantly since 1985, with the loss of old on-site native oaks that covered this area in shade.

 

 

All three trees have slender trunks with fissured, rough bark.

  

If you can train them properly, silverbells make excellent shade trees. They are small trees with big green leaves.

The dark green leaves have an ovate shape and a pointed tip. The upper surface is smooth to the touch.

Underneath, leaves are pale green and smooth. The leaf pictured measures approximately 6 inches in length, with the petiole included.

Edges are subtly serrated.

In the month of July, our three silverbells show an abundance of immature fruits, and what interesting fruits they are!

 

 

Fruits appear singly or in clumps. They are bulbous with wavy ridges. The species name diptera is a reference to the unusual fruit shape: the four wavy ridges divide into two sets of wings, making the fruit "two-winged".

 

A nice little branch was snipped for measurements.

 

Immature fruits are more than an inch in length.

 

Fruits are less than an inch wide. In the fall, these fruits will dry out and turn brown. This past winter, a handful of persistent fruits were collected and planted, but we didn't have any luck with germination. With such an abundance of fruit this year, we will necessarily try our luck again.

 

 

You can see flowers from these trees on an older blog post, found here.  

 

For more information about this species, please consult the following online sources:

Louisiana Plant Identification and Interactive Virtual Tours (LSU AgCenter) 

Texas A&M University (Aggie Horticulture)

North Carolina State University Extension