I call it Pastry Dough Lichen
Most people call it Hoary Rosette Lichen. It lets you see inside its body...
Could I eat it?
This white lichen looks like pastry dough, rolled out and lightly powdered with sugar. No book or website on lichens describes it that way, but it’s how I see it. It stands out against the colorful and darker lichens with whom it mingles.
Its name in the books is usually Hoary Rosette Lichen or Gray Rosette Lichen. "Rosette" lichens” are named for their habit of growing out from a central point, like a rosette window in a cathedral. This is a lichen I find all the time in my woods. It covers tree trunks and fallen twigs.
Teens in love
A lichen is different from an animal, plant, or fungus. It’s not just one individual. Every lichen is at least two beings living together in one body. One fungus. In this lichen, also one green alga. Sometimes several species all live together.
The fungal partner gives the lichen its shape. It’s most of what you see on the outside. Inside this lichen is the algal partner. Algae can do photosynthesis, which is the means by which sunlight turns water and carbon dioxide into sugar and living tissue. Fungus and algae entwine like a couple of adolescents in love, who can't stand not to be together or they would just die.
Seeing inside
One day I was looking at a Hoary Rosette Lichen under the microscope, and I noticed one of the lobes was broken. I focused on the broken edge, and I could see inside the lichen. There was a green layer under the skin. It gave me a brain flash. The green layer was the algae I’d been reading about!
The fungus has its own DNA, and the alga has its own separate DNA, as different as a poodle and a rosebush — they’re not even relatives. But these two need each other. The algae need shelter so as not to dry out in open air. The fungus needs photosynthesis so it has something to eat. The two organisms combine to make something that does not look or act like either of the partners but which lets them both live where neither could exist alone.
The lichen’s upper surface (cortex) is made up of microscopic strands of fungus. Below the cortex, the algae live all minutely entangled with strands of fungus.
Lichen eats its greens
When rain falls on Hoary Rosette Lichen, the surface becomes transparent and turns green, because we’re seeing the algae right through the lichen’s surface. The lichen looks mottled, because the light-colored spots (maculae) reveal the gaps in the underlying layer of algae.
When the cortex goes transparent, the algal layer receives sunlight and starts photosynthesizing like mad. The resulting sugar feeds both the algae and the fungus. That lets the lichen grow.
Physcia trademark
Those white specks in the surface are a good clue to identifying lichens in the Physcia genus. They're particularly conspicuous when the lichen is damp and has turned green.
Let me know
If someone has differing opinions on this lichen's identity, or more insight into the life history of this lichen, I'd love to hear from you. You can click on the little thought bubble below and add your comments.
Scientific name
Lichenologists call this lichen Physcia aipolia.
Very informative article. I'm sure I'll read it several more times. Interesting to see the enlarged image of the broken edge of the algae inside.
While I am a birder in a grade school way, I became a serious fan with your microscopic photos. About 2 years ago you also gave me advice on the best binoculars to purchase. Everyday I look forward to your dialog and the NYTimes. While I am a retired NP MSN I love your scientific explanations as I said “ Brain Candy” Thanks and Happy Holidays- I am in Cleveland and it is zero below. I can’t imagine what it is like in lovely Minnesota!🎅🏻