Puccinia monoica (Rust Fungus) - photos and description

Uninfected plant (foliage all grey) on the left of the photo.


General: Parasitic rust fungus that infects prairie plants in early spring, usually species of Rock Cress (Boechera/Arabis). The fungus transforms the host plant to produce the sexual structures of the fungus.

I've been asked to identify this 'plant' a few times. People don't recognize it as a Rock Cress and perhaps are confused because of the bright yellow pseudoflowers the plants produce due to the fungus.

Flowers: The infected plant produces clusters of leaves resembling bright yellow pseudoflowers, mimicking the inflorescence of spring-flowering Buttercups. Both sides of the leaves and upper stems are covered in spermagonia. The pseudoflowers produce a pungent fragrance and exude a sugar-rich solution to attract pollinators to spread the fungus.

Leaves: Varies by the species of Rock Cress.

Height: We measured stems to 15 cm.

Habitat: Prairies.

Abundance: Fairly common / uncommon.

Origin: Native.

When and where photographed: Took the above photos on April 12th, prairie hillside, Buffalo Pound provincial park, about 65 km west of our home in Regina, SK.