Lichen (pronounced "LIE-ken") is the crusty, leafy or shrubby growth you see on rocks, tree bark and old walls. It looks like a plant, but it is something stranger: a partnership between a fungus and an organism that can photosynthesize, living together as one. It is also the source of the vegan vitamin D3 in our Sol Food tablets.
What is lichen made of?
Every lichen is built around a fungus, which gives the lichen its shape and structure. Living inside it is a photosynthesizing partner: usually a green alga, sometimes a cyanobacterium, and in some species both. In the well-studied lung lichen, for example, the fungus forms a protective layer over a layer of green algae, with clusters of cyanobacteria scattered through it.
The partnership can be more crowded than that. In 2016, researchers found that many common lichens also contain a second fungus, a yeast living in the lichen's outer layer, which had gone unnoticed for more than a century. Lichens also host communities of bacteria that appear to be an integral part of the partnership.
Why do the partners need each other?
Fungi cannot photosynthesize, so they have to get their food from somewhere else. Algae and cyanobacteria can make sugars from sunlight, but on their own they are exposed to drying out and harsh light. Inside a lichen, each covers the other's weakness: the photosynthesizing partner produces energy-rich carbohydrates that feed the fungus, cyanobacteria can also fix nitrogen from the air, and the fungus provides a sheltered home.
That arrangement lets lichens grow in places few other organisms can, from bare rock to tundra, though they grow slowly.
Is lichen a plant, a moss or a fungus?
None of those exactly. Lichen is not a plant and not a moss, although it is often mistaken for one. Scientists classify each lichen by its fungus, but the lichen itself is a combination of very different kinds of life:
- The fungus belongs to the fungi, which are more closely related to animals than to plants.
- Green algae photosynthesize like plants and are related to them, but they are not land plants.
- Cyanobacteria, sometimes called blue-green algae, are bacteria: their cells have no nucleus, yet they photosynthesize and release oxygen much as plants do.
One lichen can therefore bring together organisms from separate branches of the tree of life.
Why does lichen matter for vitamin D?
Like your skin, lichen makes vitamin D when exposed to ultraviolet light. Researchers studying reindeer lichen measured both vitamin D2 and vitamin D3 in it, with more in lichens growing under stronger UV light.
That matters because most vitamin D3 in supplements is made from lanolin, the wax in sheep's wool. Lichen is one of the few sources of vitamin D3 that does not come from an animal, which makes it the basis of vegan D3 supplements. Vegans can also get vitamin D2 from yeast and UV-exposed mushrooms, but trials show D3 raises blood levels more than D2; we explain the difference in vitamin D2 vs D3 and the case for plant-based D3 in why take vegan vitamin D.
Our Sol Food tablets provide 2,000 IU of vitamin D3 from lichen, not lanolin, in one small organic, vegan tablet a day. Most adults need 600 IU a day, or 800 IU after 70, and the adult upper limit is 4,000 IU a day; see how much vitamin D you need.
