Galls on Poison Ivy and Fragrant Sumac

I’ve always thought the distinctive-looking eriophyid mite bladder galls on the leaflets of Eastern Poison Ivy (Toxicodendron radicans, family Anacardiaceae) look remarkably like the small, itchy blisters that rise on our skin (= Toxicodendron dermatitis) after contacting the plant’s oily resin called urushiol. I like to imagine that gall-infested poison ivy plants suffer the same exasperating irritation, but they have no fingers to satisfy the agonizing itch!

 

 

 

The galls are the handiwork of the so-called Poison Ivy Leaf Gall Mite (Aculops rhois (= A. toxicophagus), family Eriophyidae). The irregular, wart-like galls arise from the upper surfaces of the leaflets. The galls are at first light-green but turn deep red as the galls “mature.” Heavily galled leaves may be twisted and deformed.

 

 

 

The leaf gall mite also produces bladder galls on Western Poison Ivy (T. rydbergii) and Poison Sumac (T. vernix). Of course, western poison ivy isn’t found in Ohio, and poison sumac is rarely found in our state.

 

Oddly, the same eriophyid mite also produces bladder galls on Fragrant Sumac (Rhus aromatica, family Anacardiaceae). This is the only host of the eriophyid mite that belongs to the Rhus genus.

 

 

 

Based on personal observations, the damage to fragrant sumac does not affect overall plant health. Likewise, I’ve never seen enough damage to poison ivy to thwart the aggressive nature of this native plant in Ohio. However, there are reports in the literature that the mite should be investigated as a biocontrol agent for poison ivy.

 

 

Scratching the Surface

Eriophyids are unique among mites both in their anatomy and in the range of symptoms they produce on plants. First, eriophyids are very small. Spider mites can be seen with the naked eye, as shown in the image below. Details can be seen with a 10x hand lens.

 

 

With the naked eye, eriophyid mites look like specks of dust. The eriophyid mites in the image below are called Coneflower Rosette Mites. The picture was taken with a 30 mm macro lens, and even at that magnification, the mites still look like specks of dust; only slightly larger. A 40x magnification is required to see eriophyid mite details.

 

 

Second, spider mites have round to oblong-shaped bodies and four pairs of legs that extend laterally from the sides of their body. Eriophyid mites are cigar-shaped, and they only have two pairs of legs that extend from the front of their body. No other mite has only two pairs of legs at any stage in its development.

 

 

Digging Deeper

Eriophyids can generate a wide range of plant symptoms depending on the mite species. However, one thing they typically have in common is a narrow host range, often involving a single plant genus or one plant species.

 

For example, the leaves of black tupelo (Nyssa sylvatica) are home to two eriophyid gall-makers. Tupelo Bead Galls are produced by the eriophyid, Aceria nyssae, and Tupelo Leaf Edge Roll Galls are produced by the eriophyid, A. dina. These eriophyids are found on no other plant species.

 

 

 

 

 

The Willow Bladder Gall (a.k.a. Willow Bead Gall) eriophyid mite, Aculops tetanothrix, only affects plants belonging to the genus Salix. Its handiwork may be observed on many willows found in Ohio including black willow (S. nigra), pussy willow (S. discolor), and weeping willow (S. babylonica)

 

 

 

The eriophyid mite, Vasates quadripedes, which is sometimes called the Maple Bladder Gall Mite, produces bladder galls on the upper leaf surfaces of both silver maple (Acer saccharinum) and red maple (A. rubrum). Like the bladder galls on poison ivy, the maple bladder galls change colors as they age from light green to deep red.

 

 

The eriophyid Eriophyes negundi confines its gall-making handiwork to a single Acer species, boxelder (A. negundo). The Boxelder Bladder Galls undergo a distinctive change in appearance as they age. They transform from small, green bladder galls to large wart-like protrusions with velvet-like patches on the corresponding lower leaf surface. They are sometimes called "Boxelder Velvet Galls." 

 

 

 

On a side note, I believe boxelder challenges the poison ivy maxim, “leaves (leaflets) of three, leave it be.” The compound leaves of boxelder may have 3 – 5 leaflets; however, the 3-leaflet versions have caused me to quickly pull my arm away from mixed foliage on several occasions. Can you tell the difference in the image below?

 

 

At one time, poison ivy, poison oak, poison sumac, and fragrant (aromatic) sumac were grouped in the genus Rhus. So, it made sense that the poison ivy leaf gall mite could infest all of these “closely related” species.

 

 

However, plant taxonomists have upset the gall-cart by pulling poison ivy, oak, and sumac out of Rhus and placing them in the genus Toxicodendron. Although fragrant sumac and poison ivy remain members of the same family, Anacardiaceae, the host range of the eriophyid mite makes a bit less sense based on the previous examples.

 

I tried to gain a further understanding by untangling the taxonomic wanderings of poison ivy, oak, and sumac, but found myself going down a rabbit hole. It seemed fitting since taxonomists once grouped rabbits with rodents (order Rodentia) until the early 20th century.

 

“If the world were perfect, it wouldn’t be.” -- Yogi Berra

 

 

References (Additional Late-Night Reading)

Habeck, D. H. (1988, March). Insects associated with poison ivy and their potential as biological control agents. In Proceedings of the VII international symposium on biological control of weeds (pp. 6-11).

https://www.invasive.org/proceedings/pdfs/7_329-337.pdf

 

Jelesko, J. G., Thompson, K., Magerkorth, N., Verteramo, E., Becker, H., Flowers, J. G., ... & Metzgar, J. (2024). Poison ivy (Toxicodendron radicans) leaf shape variability: Why plant avoidance‐by‐identification recommendations likely do not substantially reduce poison ivy rash incidence. Plants, People, Planet, 6(1), 210-220.

https://doi.org/10.1002/ppp3.10439

 

Resler, L. M., Fry, J. T., Leman, S., & Jelesko, J. G. (2022). Assessing poison ivy (Toxicodendron radicans) presence and functional traits in relation to land cover and biophysical factors. Physical Geography, 43(5), 614-637.

https://doi.org/10.1080/02723646.2021.1883802

 

Weisberg, A. J., Kim, G., Westwood, J. H., & Jelesko, J. G. (2017). Sequencing and de novo assembly of the Toxicodendron radicans (poison ivy) transcriptome. Genes, 8(11), 317.

https://www.mdpi.com/2073-4425/8/11/317

 

Ziska, L. H., Sicher, R. C., George, K., & Mohan, J. E. (2007). Rising Atmospheric Carbon Dioxide and Potential Impacts on the Growth and Toxicity of Poison Ivy (Toxicodendron radicans). Weed Science, 55(4), 288–292. doi:10.1614/WS-06-190