Exobasidium azaleae

Exobasidium discoideum

Exobasidium peckii

The common azalea or Pinxter flower (Rhododendron nudiflorum [R. periclymenoides]) is  known in many places as the "Swamp apple," because so generally producing upon the tips of the branches swollen masses, large as, and superficially somewhat resembles, green apples, the work of E. Azaleae.

[O]n Rhododendron viscosum is E. discoideum, Ell., which develops upon the under surface of the leaves large, turbinate or discoid galls two or more centimeters in diameter.

[On] Andromeda mariana ... The tips of the stems, instead of bending somewhat to one side and hanging full of the large white corolla bells characteristic of the species, were bolt upright, shorter than usual and bearing capitate masses of a pale green color. Upon inspection these were seen to be abnormally developed stems with their misshapen flowers in dense clusters. Some of the stems bore ordinary flowers a few inches below the malformed tips. 

[Exobasidium peckii] is remarkable in being confined almost entirely to the inflorescences where it causes most extravagant enlargement and distortion of parts. Some of the single flowers are more than an inch in length and in spread of petals, the bell-shaped corolla being replaced by one that is wheel-shaped and polypetalous ... The ovary ... is raised a half inch or more above the receptacle and the peculiar placentae greatly exaggerated. 

Notes Upon a New Exobasidium