Small orange particles on the leaves of Common Blackberry (Rubus allegheniensis). These warts are spore-bearing structures; the main body of the fungus invades the plant tissues, spreading through the leaves, canes and roots. Infected plants are stunted and do not produce fruit. They will produce apparently healthy canes later in the summer, but these are also infected and will produce the fungal spores on the leaves the next year.

A parasite of Common Blackberry, and sometimes other members of the genus Rubus. Probably occurs anywhere blackberries do. Occasional in Wildwood.

Unlikely to be confused with anything else, given its host plant and bright color. Black raspberries are usually resistant, but are infected with a macroscopically very similar fungus, Arthuriomyces peckianus. This has not been seen in the Park, yet, possibly because black raspberries are rarer than blackberries.