Brain Puffball (Calvatia craniiformis)

🏷️ Description

Calvatia craniiformis, often called the brain puffball or skull-shaped puffball, is a fascinating fungus that looks like it popped right out of a Halloween movie! 🎃 With its brain-like curves and skull-like shape, this medium-to-large puffball (8–20 cm wide) earns its name from cranium—the Latin word for "skull." Found across North America, Asia, and Australia, it thrives in grassy areas, open woods, and even along roadsides. 🌾🌎

When young, its smooth white skin hides firm, edible flesh—perfect for cooking! 🍳 But beware: once it matures, the inside turns olive-yellow, becoming a dusty spore mass. While it’s a culinary delight in its youth, it’s also been a natural remedy in folk medicine. Traditional uses range from wound dressings in China and Japan to a (now risky) nosebleed treatment by the Ojibwe tribe. 💚⚖️

But that’s not all—this puffball packs a scientific punch! 💥 Research has uncovered bioactive compounds with antitumor properties and plant growth inhibitors, making it as brainy as it looks. 🧬🌿

🌳 Ecological Fun Fact: Though mainly saprobic, studies suggest C. craniiformis can form mycorrhizal relationships with certain trees like poplars under specific conditions.

🐞 Role in Nature: The Brain Puffball isn't just for show—it serves as a food source for flies and plays a key role in nutrient recycling in its habitats.

🔎 Identification

🍐 Fruiting Body:

• Shape: Starts off ball-shaped and matures into an inverted pear or a skull-like form—hence the nickname! 💀

• Size: Ranges from 1.97 to 5.91 inches (5 to 15 cm) tall and 1.97 to 3.94 inches (5 to 10 cm) wide, sometimes larger.

• Base: Thick, often wrinkled, attached to cord-like rhizomorphs that may be covered in soil.

Outer Surface: Smooth, whitish to pale brownish, bruising brown when touched. Over time, the skin may crack into patches (areolate texture).

Interior:

• Young: Firm and white.

• Maturing: Turns yellow-green, then olive-brown as it fills with spore dust.

• Over-mature: The top ruptures, releasing spores 💨, leaving behind a cup-like base that can linger for weeks.

👃 Odor & Taste: Neutral—nothing distinctive.

🦠 Spore Print: Olive-brown.

🌎 Habitat & Distribution: It often pops up alone or in clusters in grassy spots like lawns, roadsides, ditches, and waste places, and along the edges of woods. While widely found from the northeastern U.S. to the Rockies and Southwest, it's rare west of the Rockies. This fungus also grows in parts of Asia (China, Japan, India, etc.) and Australia. It favors summer and fall and can even be found in unique spots like black locust plantations in Michigan.

🔬 Microscopic Features

• Spores: Small (2.5–3.4 μm), round, translucent (hyaline), with fine, wart-like bumps (verrucae).

• Capillitial Threads: Long, branched, and hyaline (2.4–4 μm thick), sometimes septate with pits.

• Under light microscopy, spores resemble those of C. gigantea and C. rubroflava, but electron microscopy reveals unique spore ornamentation.

👀 Look-Alikes

💜 Calvatia cyathiformis

• 🌾 Grows in similar habitats.

• 🟣 Mature gleba: Purple-brown.

• 🧩 Surface: Develops mosaic-like scales or patches.

• 💨 Spore dust: Purple.

💗 Calvatia fragilis

• 📏 Size: Smaller than C. craniiformis.

• 🌸 Mature gleba: Pink to purple.

⚪ Calvatia bicolor

• 🟡 Shape: Smaller and rounder, often mistaken for young C. craniiformis.

• 🌾 Spores: Coarsely ornamented.

• 🚫 Subgleba: Lacks a distinct one.

🟤 Lycoperdon utriforme

• 💡 Key feature: Develops a cavernous opening exposing its olive-brown gleba.

• ✂️ Capillitial threads: Have distinct slits.

📜 Synonyms

• Bovista craniiformis Schwein. (1832)

• Calvatia craniiformis (Schwein.) Fr. (1849)

Photo sources:

Photo 1 - Author: Sarah Culliton (CC BY 4.0)

Photo 2 - Author: Chris Poling (CC BY 4.0)

Photo 3 - Author: danpatrick (CC BY 4.0)

Photo 4 - Author: Annika Lindqvist (CC BY 4.0)

Photo 5 - Author: Annie Weissman (Public Domain)