Tree of the Week: Honey Locust (Gleditsia triacanthos)

This past spring, prompted by its display of tiny, fragrant flowers, we discussed the history of the arboretum's honey locust (Gleditsia triacanthos). In 2013, we collected seeds but incorrectly identified the source as a black locust. These were germinated in the campus greenhouse and one specimen was planted in the arboretum in April of 2015. It has now been a decade since the seeds were collected, and this year, we have our first fruits. 

During this past summer, we observed pods growing on the tree. They were high up, on the upper branches, far out of reach. This week, two fruits were incidentally discovered on the ground. One pod was found under a nearby groundsel bush, and then we picked up another pod directly under the honey locust, next to its trunk. What luck! These two fruits are shown in the photos below.

Honey locusts produce long, leguminous fruits. The two pods in the above photograph are ripe. They each measure between six inches to one foot in length. They are black, twisted, bumpy, hard and the seeds could be heard rattling inside their individual cells. It is said that honey locust pods have a sweet pulp, but nothing on the interior of these ripe fruits suggested sweetness; perhaps, in order to experience the honey of the honey locust, the fruits need to be collected before desiccation.

 

From two pods, 19 seeds were collected. The seeds are brown, with an oval shape, and measure more than ¼ inch in length.

 

So, within a decade, the honey locust has developed from a seed into a very tall tree that is now producing fruit. That's rapid development!

Tree of the Week: Honey Locust (Gleditsia triacanthos)

The arboretum's lone honey locust (Gleditsia triacanthos) is looking all grown up. This is an 8-year-old tree that germinated in the campus greenhouse from seed collected in Caddo Parish. Upon collection the species was not known for certain, but we are now confident that this is a honey locust.

Our honey locust grows in the middle of a gradual slope; not at the top of the hill and not at the bottom. Pictured in the background, we see the red bricks of Cline Hall dormitory, currently being remodeled.

Much of the new growth is now out of reach. The youngest leaves are red and orange. Don't worry, they're fine.

For the first several years, this specimen had long, skinny, flopping branches that refused to stay upright. Regular pruning and staking were required to develop a straight trunk, and also to minimize the hazardous nature of the thorny branches.

Toward its base, the trunk is approximately four inches wide and it is heavily protected. Do small animals make useful habitat out of these thorns?

In the arboretum record, this is the first year it has produced flowers. Photographs of the flowers were taken on April 22, 2022.

Pollinators were hard at work.

Small, greenish flowers hang in clusters. These flowers aren't showy, but have a nice fragrance.

You can see more photos of this honey locust on an older blog post, found here.

Tree of the Week; or, a Case of Mistaken Identity

When is a Locust not a Locust?

In 2013, the arboretum's curator Lacey Anderson collected seed pods of a thorny locust from the side of Old Mooringsport Road north of Shreveport. The seeds germinated in the campus greenhouse under Dr. Ed Leuck's supervision, and a seedling was planted in the arboretum in 2015. The tree pictured below is about four years old. Dr. Ed Leuck had previously collected and planted a Black Locust in 1997, but the tree was displaced by the construction of the Fitness Center and it later died.

Locust tree approximately 4 years old

This young locust tree has required significant pruning to develop a single trunk. Several long, spindly branches haven been removed over the past several months.

The initial identification of this tree as Black Locust (Robinia pseudoacacia) was made on the basis of the seed pods and thorns of the donor plant. As the tree has grown up, some doubts have entered the mind. Let's examine the evidence.

Left pane: Robinia pseudoacacia diagram
 Right pane: photograph of the specimen

The Petrides reference volume states that Robinia pseudoacacia  has opposite thorns of between half-inch to one-inch length, while our specimen has single thorns of two-inch length. Robinia pseudoacacia has around thirteen leaflets with a single terminal leaflet, while our specimen has sixteen to twenty leaflets and a terminal pair. Robinia pseudoacacia has smaller flat seed pods while the parent tree had large, twisted seed pods.

Thus, the arboretum's specimen is a Gleditsia, probably the Honey Locust (Gleditsia triacanthos). There is a possibility that it may be a hybrid between the Honey Locust and the similar Water Locust (Gleditsia aquatica) but the tree will have to grow up more before we can make this determination.

Thorns of the Honey Locust are fearsome and longer than an inch.

Cultivars have been selected for fewer thorns, but this wild strain is very concerned with self-preservation.

The base of the tree is also heavily thorned, discouraging climbers and nibblers.

This young tree has not yet developed bark with a lot of character. It might be called scaly.