Inonotus quercustris

🏷️ Description

Originally described as a parasite clinging to the trunks of urban water oaks in Baton Rouge, Louisiana, Inonotus quercustris has since stretched its reach across the southern United States, including Texas, and even Argentina! Now, its latest haunting ground appears to be the Mingo National Wildlife Refuge in southern Missouri — a place as ecologically quirky as the fungus itself.

🧭 Mingo: A Northern Home for Southern Species?

Tucked into southeast Missouri, the Mingo swamps are a fascinating outlier — a Gulf-Coast ecosystem plopped far north of its expected range. And just like the swamp, I. quercustris feels right at home there, targeting living red oaks like water oak (Quercus nigra) and willow oak (Quercus phellos) with quiet aggression.

🌲 Tree-top Trouble: A Parasitic Lifestyle

This mushroom isn’t your friendly decomposer — it’s a parasitic pathogen, causing a white heart rot in living oaks. Unlike many polypores that fruit near the base of a tree, Inonotus quercustris makes a high-rise appearance, often sprouting its massive fruiting bodies well above eye level, making it hard to spot unless you're craning your neck (or have binoculars).

It fruits year-round, typically alone or in shelving clusters, and is most commonly expected in warm, humid Gulf Coast regions.

🔎 Identification

🍂 Cap:

• Size: Up to 15.75 inches (40 cm) across and 7.87 inches (20 cm) deep!

• Shape: Semicircular to fan-shaped; flat or planoconvex.

• Texture: Velvety to finely hairy when young, becoming nearly smooth with age.

• Color: Starts yellow to orangish yellow, matures into a deep rusty brown.

• Margin: Thick and soft when young — squishy like a sponge cake.

🟡 Pore Surface:

• Bright yellow to creamy when fresh.

• Turns yellowish-brown, bruises brown when handled.

• Pores: 3–5 angular pores/mm, with tubes up to 3 cm deep.

🚫 Stem: None — this one’s sessile!

🧃 Flesh:

• Reddish brown, soft and watery when young.

• Gets tougher with age.

• Faintly zoned or streaked, especially when sliced — reminiscent of Fistulina hepatica (beefsteak fungus 🍖).

👃👅 Odor and Taste:

• Odor: Not distinctive.

• Taste: Tangy or sour — not for the dinner plate!

🔬 Chemical Reactions:

• Flesh and cap surface turn red to maroon, then quickly black with KOH — a handy ID trick for field mycologists.

🧫 Spores:

• Ellipsoid, smooth, pale yellowish to brownish in KOH.

• Inamyloid (doesn’t react with Melzer's reagent).

• Size varies by region:

  Louisiana: 9–10 × 6–8 µm

  Argentina: 7–10 × 5–7 µm

  Missouri: 5.5–7 × 4–5.5 µm

🌡 Hyphal System:

• Monomitic (only one type of hyphae).

• Clamp connections absent.

• Lacks hymenial setae (spiky sterile cells often seen in polypores).

• But boasts dark reddish brown setal hyphae (tramal setae) — thick-walled, fusoid-tipped, and up to 200+ µm long!

🌎 Distribution & Ecological Note

Though initially tied to the urban water oaks of Baton Rouge, Inonotus quercustris is turning out to be more widespread — thriving from Texas to Argentina, and now up into Missouri's cypress-tupelo swamps. Its association with southern tree species like water and willow oaks suggests it may be a Gulf Coast specialist slowly creeping north, possibly with the help of climate shifts or habitat continuity through river systems.

📌 Final Thoughts

While not a mushroom you’re likely to stumble across on a casual stroll — especially given its lofty perch — Inonotus quercustris is a fascinating and under-documented polypore, blending striking appearance with a parasitic edge. Keep your eyes up next time you wander southern swamp forests or Gulf oak woodlands — this stealthy fungus could be watching from above!

Photo sources:

Photo 1 - Author: Karen Guin (CC BY 4.0)

Photo 2 - Author: Ezequiel Racker (CC BY 4.0)

Photo 3 - Author: Amber M. King (CC BY 4.0)

Photo 4 - Author: Michelle W. (CC BY 4.0)