The rust fungus Puccinia monoica infects the plant leading to pseudoflowers, which mimic those of yellow, early spring wildflowers (e.g. buttercups), not only in visible light but also in ultraviolet.
Spores produced in the aecia are referred to as aeciospores and are responsible for infecting the alternate host plant (a grass species: Koeleria, Trisetum, or Stipa).