Pilobolus kleinii

Morphological Features:

Fruiting bodies of very small size, but not microscopic like most fungi of its division. In an initial stage, they fruit as a thread-like structure barely a couple of millimeters long, with a yellowish lower portion and a translucent upper portion; then it elongates upwards, growing simultaneously while forming a bright yellow head-like structure at the apex, leaving the stipe translucent. Finally, a lens-shaped sporangium is formed, which is initially yellow and later turns black, occupying the apex; beneath it lies an inflated translucent sac containing liquid, and a similarly translucent pedicel.

Reproductive cycle Once the sporangium turns black, the fungus is ready to begin its reproductive cycle. Inside the sac, an osmotic pressure builds up that can reach 7 atmospheres; eventually, the sac cannot withstand the pressure and bursts. The liquid inside is ejected through an opening located beneath the sporangium, propelling it like a cannonball to a distance of 2 to 3 meters. In just 0.25 milliseconds, the sporangium reaches a speed close to 100 km/h, representing the greatest acceleration known in any living organism. Using a hypothetical human equivalent, it would be approximately as if a person could throw a tennis ball a distance of 4 to 5 km. Furthermore, it is a phototactic fungus, so it always directs its discharge toward the light, carrying the sporangia to more open areas where they adhere to herbaceous substrates. There, they are ingested by livestock, surviving the entire passage through the intestinal tract without germinating or being destroyed. Upon defecation by the animal, the fungus germinates, forming mycelium on the dung and giving rise to new fruiting bodies, thus completing the cycle.

Stipe with a translucent appearance whose length depends on the distance to sunlight; the greater the distance, the longer the stipe.

Habitat:

This curious fungus fruits on the dung of various types of livestock; we have found it on horse manure. It always fruits on dung located in damp areas, often in the shade of trees, but it launches its sporangia toward the sunniest and most accessible areas for livestock. Although located in May, we have no record of it showing a preference for any specific season. A rare and curious species.

Observations:

Zygomycetes are generally microscopic fungi, with exceptions such as the one presented here; they are commonly referred to as molds. Species of the genus Pilobolus always fruit on the dung of various animals, from rabbits to cattle; the species in question is typically associated with horse manure. The sporangia possess calcium oxalate crystals that protect them during passage through the intestinal tract, preventing damage and allowing subsequent fruiting once released. It is one of those surprising natural curiosities: how such a minute fungus can function as a true cannon.