Editor’s Note:
Mycology is fascinating to me because fungi constantly remind me of the inherent weirdness of life, and Macrocybe titans is a good example. As a human being, it seems “natural” to have a provincial, species-centric view of the universe, whereby our path down Evolution Road seems the most logical and beneficial. However, when I learn more about mushrooms, I find that my inflated esteem for kingdom Animalia has yet another pinhole through which my pride escapes, because the tremendous adaptability and resilience of fungal organisms is astonishing.

Today I want to talk about Macrocybe titans, which produces probably the largest gilled fruiting bodies in the Western Hemisphere. This monster grows wild in Florida, Mexico, Costa Rica, and other tropical habitats, and from all accounts its range is spreading northward and westward. If you’re a mycophobe, you might want to skip this entry, because Macrocybe titans is one of those species that might give you giant mushroom nightmares!
Yours In Fungal Fancy,
Mushroom Anna

Macrocybe Titans, the Big-Ass Mushroom

Macrocybe titans is a gilled mushroom in the Tricholomataceae family, and as such it’s a classic cap-and-stem mushroom with tightly packed whitish-cream gills that get wavy in age. The mushroom is normally a buff or cream color, and it often has dark, backward-bent scales on the stem. In addition, the stem frequently has noticeable vertical striations that one author describes as similar to the stripes on a candy cane (in shape, not color).
Macrocybe titans has a habit of coming up in clusters of several individuals, sometimes from a common base, and the base of the stems are often bent laterally so there is a crook where the mushroom meets the ground. Many collections of this species include a variety of mushrooms of different sizes, and some of them are pitifully tiny. It is almost as though the Macrocybe titans mycelium is overly enthusiastic and produces numerous mushrooms, then promptly and runs out of juice to grow all those specimens to full size.
The thing that makes Macrocybe titans so remarkable is its size: its cap can exceed 3 feet in diameter, and some specimens have weighted in excess of 40 pounds and grown well over 2 feet tall. This mushroom is edible, but care must be taken with identification, because it’s entirely possible there are other Macrocybe mushrooms that look similar that might not be so wholesome. Full disclosure: I have never eaten this species, nor have I personally spoken with anyone about the experience of consuming it.

Macrocybe titans is a member of genus Macrocybe, which aptly translates as “huge head.” The genus Macrocybe is quite small (as mushroom genera go), clocking in at roughly 12 distinct species that are currently known to science. Of course, as I have said before and will no doubt say again, this is likely to change as mycologists find more specimens that are genetically distinct from one another.

Macrocybe titans – Roaming Mycelium

Macrocybe titans was first found in 1969 in Gainesville, Florida, and at that time it was identified (incorrectly) as a known species. In 1980, it was published as a new species called Tricholoma titans by mycologists Bigelow and Kimbrough. Subsequently, it became clear that the species was different from other members of the Tricholoma genus and the mushroom was moved to a new genus called Macrocybe. 
Macrocybe titans is a reasonably common sight in yards and green spaces around Florida, but in recent years it’s been found in new locations in the United States, including in the lawn of an abandoned home in Athens, Georgia.
There are varying theories as to why this mushroom is being found outside of its traditional digs in tropical bits of Florida. Some mycologists have opined that it’s due to climate change, because this mushroom favors tropical habitats and as the climate shifts, this mushroom might be opportunistically moving northward and westward.
Others believe that the mushroom be spreading by way of ornamental plants. The idea here is that the mycelium (the underlying network of cells that is the true fungal organism) is being transported by landscape suppliers who grow their stock of grasses and other ornamental plants in Florida. A third theory seems reasonably plausible to me as well. Now that a lot more people are interested in mushrooms and mycology, we might be seeing fuller natural ranges of species because people are starting to sit up and take notice of mushrooms more than in times past.
The question of how and why Macrocybe titans is spreading is a head-scratcher, but this is not a unique phenomenon. The poisonous and common green-spored parasol mushroom, Chlorophyllum molybdites, used to be considered a “southern” mushroom that favored lawns and yards in the steamy and hot Deep South and piney woods regions of east Texas, but this mushroom has also been spreading and has been spotted as far north as Wisconsin.
The role of climate change and other ecological shifts in the “migration” of fungi fascinates me, because once new mushrooms take up residence in a habitat, they can do wonderful or terrible things to their new home. The devastation caused by the honey mushroom species complex (Armillaria genus) is a perfect example. Although in times past the parasitic Armillaria oystae is not thought to have been tremendously destructive, it can (and does) gobble up thousands of acres of forest, leaving a swath of dead trees in its wake.
One theory behind this is the chilling thought that logging and other human intervention denudes forest habitats of ecosystem-critical fungi and other organisms, and leaves a gaping niche that the honey mushroom happily fills. Essentially, it’s possible that when an ecosystem has no (or reduced) “load balancing” mechanisms in place, fungi can and will take advantage of a lack of competition, sometimes with devastating consequences.

When it comes to Macrocybe titans, however, it’s probably not worth worrying too much. This species is saprobic, meaning that it is a decomposer that does not appear to attack, rely on, or partner with trees, grasses, and other plants. Indeed, Macrocybe titans may well be a beneficial species, as the mycelial mat required to produce such a massive fruiting body may help prevent erosion and destroy soil pathogens.

Macrocybe titans and Atta Ants

For my money, the most interesting observation scientists have made about Macrocybe titans is the fact that in Costa Rica, a version of Macrocybe titans can be found in the fungus gardens of Atta ants, which is a genus of leaf-cutter ants. Over 200 species of ants practice fungal agriculture, whereby the ants grow, nurture, feed, and protect mycelium and use it as a food source.
Here’s how it works: leaf-cutter worker ants are divided into two groups: media workers and minima workers. The media workers are large and burly and forage for leaves and other plant matter outside the nest, which they cut into big honkin’ pieces and haul back to the colony. Then, the much smaller minima workers take the mushroom food and chop it into nice little digestible pieces and feed it to the mycelium that the ants are cultivating. Minima ants also work as fungus guardians and attack parasites and flies that are attracted to the fungus.
In the case of Macrocybe titans, it seem likely that leaf-cutter ants in Costa Rica feed and sustain different mycelia of this species, which becomes a reliable fungal food source for the colony. I swear, mycology and entomology are so crazy to me; the idea that leaf-cutter ants cultivate one of the biggest mushrooms in the hemisphere leaves my mouth agape!

Macrocybe titans in Culture

This mushroom can be cultivated by us humans, too, and there are some mushroom suppliers who sell Macrocybe titans spawn. Spawn is mycelium growing on grain that’s used like seed to inoculate “substrate,” which is the mushroom’s food and habitat.
This mushroom is like many other secondary decomposers that eat rich compost as opposed to straight-up dead wood that’s packed with big, hard-to-digest molecules like cellulose and lignin. Thus, the growing requirements of Macrocybe titans are similar to mushrooms like the white button mushroom Agaricus bisporus (and other mushrooms in the Agaricus genus), the shaggy parasol mushroom Chlorophyllum rhacodes, or the shaggy mane, Coprinus comatus.
Although all the cultures I saw for sale were pretty darn spendy, when I make my first million I will definitely see if I can get Macrocybe titans to take up residence in my compost pile!

…But in the Meantime…I’ll Just Ponder the Awesomeness of this Monster Mushroom!

While I am awaiting the aforementioned making of millions, I will simply stare at the shockingly large specimens of Macrocybe titans that people have found in the wild, bow my head in respect for the leaf-cutter ants, and go about my southern-states mushroom hunting with fingers crossed that I might find this species myself one day.