Jack-in-the-Pulpit Rust

Jack-in-the-Pulpit Rust is a fairly common, conspicuous, rust fungus. It occurs in the United States and southern Canada east of the Great Plains and in Mexico. It is found wherever its hosts are found. These include jack-in-the-pulpit, green dragon, green arrow arum, and calla lily.

On infected plants, Jack-in-the-Pulpit Rust appears as many pustule-like, spore-producing structures (uredinia) on the leaflets, the flower column (spadix), and the hood (spathe). The rust also attacks the underground storage organ (corm). The uredinia are yellowish orange, round, and small, no more than 3⁄64″ (1.3 mm) in diameter. They appear on the plant from April through June.

Jack-in-the-Pulpit Rust overwinters in the corm and spreads to the leaves in the spring. It causes reduced plant growth by reducing the leaf area. It inhibits pollination by deforming the hood and the spadix. It reduces vegetative propagation because the plant has less vigor, and it can inhibit the production of flowers for the same reason. Most infected female plants are unable to produce seeds.

jack-in-the-pulpit (Arisaema triphyllum), green dragon (Arisaema dracontium), green arrow arum (Peltandra virginica), and calla lily (Zantedeschia aethiopica)

April through June

Sources

4, 7, 24, 26, 29, 30, 77.

Common

Jack in the pulpit rust, Uromyces ari-triphylli.
Mike's thoughts on plants.

Greg Watson
5/6/2025

Location: Carley State Park

I took the photo of Jack-in-the-Pulpit Rust, Uromyces ari-triphylli in Carley State Park.