Tar spot on sycamore leaves
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Image of the day – 207
What’s in an image? Sometimes quite a lot, more than meets the eye. I’m posting an image whenever I can.
I take photos of autumn colour on trees quite often as you will know if you’ve browsed around on Journeys of Heart and Mind, especially in the Image of the day section. The colours are heart warming just as the temperatures are getting lower with winter hovering on the seasonal horizon.
So here’s one more autumn foliage image, but wait… What are those black marks? They don’t look like autumn colour! They look like splashes of tar, but they’re not that either. In fact it’s the ‘tar spot’ fungus (Rhytisma acerinum) that infects sycamore leaves. The black spots are so tiny at first that they’re barely noticeable, but they grow larger and larger as the summer progresses and the leaves mature.
In the spring, fungal spores are released from overwintered leaf-litter, are blown about by the wind, and stick to leaf surfaces where they germinate. Thread-like fungal hyphae grow across the underside of leaves and enter through leaf pores called stomata (singular stoma). Most plants are resistant and the hyphae die, but some Acer species are susceptible, the hyphae thrive and a small yellow spot of damaged leaf tissue appears. During the summer this spot grows in diameter as the hyphae spread. In autumn the infected leaf falls, together with all the other leaves from the trees. The fungus overwinters in the moist leaf litter, and releases spores again in the spring.
See also:
- Hypha – Wikipedia
- Stoma – Wikipedia
- Tar spot, Rhytisma acerinum – Wikipedia
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