Spring Beauty is one of the early woodland ephemerals that greet us before tree buds have opened and released the leaves that will soon shade the forest floor. With April showers plentiful the ground is often damp, encouraging the growth of Spring Beauty Rust (Puccinia mariae-wilsoniae), a species of rust fungus that grows on both species of Spring Beauty (Claytonia caroliniana and C. virginica) that we have in the Northeast. There are approximately 7,000 species of rust fungi, all of which are parasites of plants from which they obtain nutrients and on which they reproduce and complete their life cycles.
Spring Beauty Rust can be recognized by the scattered clusters of reddish-brown sori (clusters of sporangia, structures producing and containing spores) that cover the surface of Spring Beauty’s leaves, stems and the sepals on the outside of flower buds.
If you survey a patch of Spring Beauty you will see that some are quite white while others have deep pink nectar guides and pollen. As a rule, Spring Beauty Rust infects plants with pinker flowers.
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Spring Beauty, Claytonia virginica, is a familiar and welcome spring ephemeral that carpets the forest floor at this time of year. Within a population, its blossoms range in color from white to a deep pink. You don’t usually find a range of colors within a given population, as one color is often more successful at reproducing and it eventually becomes dominant, while the other colors are eliminated.
There is a reason why both colors of Spring Beauty continue to flourish within a given population. A red pigment interacts with two chemicals (flavenols) to produce the range of color. Plants with a high percentage of flavenols produce white flowers. These flavenols are a deterrent to herbivores, so in years when there are lots of slugs, white-flowered plants are more successful in producing seeds. This would lead one to conclude that eventually pink-flowered plants would diminish in number. However, white-flowered Spring Beauty is also parasitized by a type of fungus called a rust, Puccinia mariae-wilsoniae, which causes orange spotting and often serious deformation of the plant (see photo).
Thus, in years when slugs are numerous, white-flowered Spring Beauty flourishes and produces seeds. In years when slugs are not numerous but fungal infection is high, pink- flowered plants reproduce more successfully. This sporadic success of both white and pink Spring Beauty is why we continue to find them both in the same population.