Rosebay willowherb or Fireweed - Chamerion angustifolium - is a very striking and widespread plant species. During flowering it is easy to recognize. The upright plants have a cluster-shaped inflorescence at the top that tapers to a point. The color of the flowers is purple or purple-red. The separate flowers in the cluster are somewhat symmetrical on both sides because the top two petals are somewhat smaller than the bottom two. The scattered leaves are narrow and lanceolate and closely resemble the leaves of Willows.
Willowherb rust is a disease caused by the fungus, Puccinia pulverulenta. Initially, pale, ill-defined yellow spots appear on the upper leaf surface, corresponding to orange, dusty pustules on the lower surface. It appears in summer. The fungus releases orange spores from the pustules and these are spread by the wind to initiate new infections on leaves.
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