Good evening, friends,
I’m really toeing the line of what is a “mushroom”/“toadstool” with this week’s fungus, the bushy beard lichen (Usnea strigosa). Regardless, I’ve wanted to write about this fascinating organism for months now. I took a lichenology class at the New York Botanical Gardens with lichenologist James Lendemer and I haven’t looked at these often-ignored organisms the same since. Lichen are indeed fungi, but they’re also a whole lot more. They challenge the idea of individual organisms and truly exemplify the interconnectedness of life on this planet.
I was up in Cape Cod this past weekend and although it poured when we got in, it had been dry for a while. There weren’t many fleshy mushrooms aside from some wine caps and Russulas. What was abundant, and is always abundant regardless of the time of year, was the bushy beard lichen, U. strugosa, hanging out in the oak trees. One of the first things to get out of the way is that U. strigosa, and all lichens on trees, are not actually harming the trees. As we’ll learn, they’re very busy living their own lives.
Lichens are fungi with a unique symbiotic lifestyle. The fungi will form a symbiosis with a photosynthetic organism - either an algae or a cyanobacteria (sometimes both), known as a photobiont - to create this novel organism. The photobiont is responsible for photosynthesis and subsequently providing sugar for the lichen. The organism is entirely self-contained, and both the photobionts and mycobionts (fungal partners) aren’t known to grow independently in nature. An interesting note is that this symbiosis isn’t unique to certain species of fungi, but it’s a trait that has evolved many times, separately, across many species.
Lichen are named after the dominant fungal partner (in our case Usnea strigosa), not the plant or bacterial symbionts. One reason for this is because that U. strigosa in Georgia will not have the same algal and bacterial partners as the U. strigosa found hanging in a tree in Cape Cod. The fungus will pair with a photobiont that is best suited for the specific environment, and often that means growing with more than one partner. Lichen are comprised of a variety of different fungal, algal, and bacterial organisms. Compare them to how an apartment building houses different humans, pets, insects, and bacteria.
In our specimen there is the dominant fungus, Usnea strigosa, but even still there are several genetically distinct members of U. strigosa (different genotypes) that can reproduce amongst themselves. Then there are secondary fungal mutualists (other species of fungi living in the lichen, known as endolichenic fungi), endolichenic algae, endolichenic bacteria, and even micro-invertebrates. And they’re all reproducing. If you thought it was crowded in there already, just realize they’re all trying to multiply as well.
The dominant fungus can reproduce asexually using conidia (asexual spores) to create genetic clones of itself - a trait we see in other fungi. Remember how there are genetically distinct individuals of the dominant fungi? Well, those individuals can recombine their DNA and produce genetically distinct spores as well. The fungal spores are released through the fruiting body seen above, and can sometimes even be released with cells of the photobiont. The lichen in its entirety relies on “vegetative reproduction” which entails a piece of the lichen breaking off and dispersing into the environment (seen below) to form a new lichen.
Even More Fun Facts
Up to this point we’ve learned mostly about lichen in general and not specifically the bushy beard, Usnea strigosa. Well there isn’t nearly as much information on individual lichens (“individual lichens”, bit of an oxymoron right folks?) as there are on mushrooms, and both are vastly overlooked relative to plants. U. strigosa has purported medicinal properties and studies have demonstrated that compounds found in species across the genus Usnea have strong anti-bacterial properties. Usnea has traditionally been used to treat a variety of ailments ranging from weight loss to sore throats and even to relieve pain and fevers. Contemporarily, a study showed that compounds found in U. strigosa could be used to treat breast cancer (Reference 6).
U. strigosa exists throughout the year but is only growing/reproducing when wet. The lichen’s growth pattern is fruticose, which relates to the shrubby, tree-like form and is uniform on all sides (some lichen are predominantly photobiont on top and fungi on the bottom). This makes them especially sensitive to air pollution. Lichen, in general, are a good indicator of air quality - the more air pollution, the less lichen. In healthy environments they can and will grow on any stagnant surface. U. strigosa grows throughout the Appalachian range and along the coast in northeast North America (higher humidity along the coast), but not in NYC. Sometimes the lichen gets transported into the city on nursery trees though.
If I was at all unsure about featuring the publication’s first lichen, discovering this bird nest today in Manitou assuaged all my concerns. I stumbled upon this on the ground under a sugar maple after the heavy rains we got last night.
While a longer publication, this was but a smidgen of all the fascinating lichen information out there. Hopefully it’s a digestible amount and you’re excited to learn more, I certainly am. For now, the next time you encounter a lichen hopefully you won’t see just a scab or hair on a rock, but a complex organism teeming with life.
I also managed to avoid all the puns (“I’m lichen you a lot”, “I’m taking a lichen to this”, yada yada) and for that you’re welcome,
A lot of information came from James Lendemer’s lichenology class at the New York Botanical Gardens. Additionally, information was sourced from:
3) Singh, Brahma & Prateeksha, Prateeksha & Paliya, Balwant & Bajpai, Rajesh & Singh, Braj & Kumar, Jatinder & Kumar, Sanket & Jadoun, V & Upreti, Dulip & Nayaka, Sanjeeva & Joshi, Yogesh. (2016). The genus Usnea: A potent phytomedicine with multifarious ethnobotany, phytochemistry and pharmacology. RSC Adv.. 6. 10.1039/C5RA24205C. https://www.researchgate.net/publication/292212820_The_genus_Usnea_A_potent_phytomedicine_with_multifarious_ethnobotany_phytochemistry_and_pharmacology
5) Sepahvand A, Studzińska-Sroka E, Ramak P, Karimian V. Usnea sp.: Antimicrobial potential, bioactive compounds, ethnopharmacological uses and other pharmacological properties; a review article. J Ethnopharmacol. 2021 Mar 25;268:113656. doi: 10.1016/j.jep.2020.113656. Epub 2020 Dec 1. PMID: 33276059.
6) Ebrahim HY, Elsayed HE, Mohyeldin MM, Akl MR, Bhattacharjee J, Egbert S, El Sayed KA. Norstictic Acid Inhibits Breast Cancer Cell Proliferation, Migration, Invasion, and In Vivo Invasive Growth Through Targeting C-Met. Phytother Res. 2016 Apr;30(4):557-66. doi: 10.1002/ptr.5551. Epub 2016 Jan 6. PMID: 26744260; PMCID: PMC5045260.