Phellinus robiniae

Common Names
Cracked Cap Polypore
Ecology: SaprotrophicParasitic

Phellinus robiniae, also known as the cracked cap polypore, is a member of the Phellinus genus. They are perennial polypore mushrooms, both parasitic and saprotrophic. Commonly found on locust trees, but may also grow on acacia, chestnut, hickory, mesquite, oak, and walnut trees.

You'll find Phellinus robiniae growing on nearly every black locust tree due to the locust borer beetle (Megcallene robiniae). As their name states, the beetles bore tunnels into locust trees. These tunnels are ideal conditions for Phellinus robiniae spores to germinate. Unfortunately for the locust trees, the tunnels often lead directly to the heartwood, which the fungus attacks, causing heart rot.

Phellinus robiniae is sessile (no stipe), and resupinate, meaning that the spore-bearing tissue (hymenium) connects directly to the substrate. The shape of the mushroom typically appears as semicircles growing from the margins (edge). Each year a new layer of pore surface accumulates at the cap margins.

Giant Phellinus robiniae

Large cracked cap polypore

The largest species I found was 56 cm in diameter, 16 cm high, and 24 cm protruding from the tree. Surprisingly the specimen was ground level allowing for close examination.

Cap Features (Pileus)

Phellinus <i>robiniae</i>
TanOrangeTawnyBrownPurpleBlack
FurrowedZonate
When young, Phellinus robiniae is tan and may exhibit a velvety texture. As the mushroom matures, the cap may appear tan, tawny, orange, brown, purple, or black. The cap will also become furrowed with age resembling rough bark. At first glance, you would think the caps are also green, but this is likely due to moss or algae that usually covers the mushroom.

Pores

Phellinus <i>robiniae</i>
Tan
Fine
The tan pore surface is covered by tiny circular pores tightly spaced (~7-8 per mm). Phellinus robiniae produces brown spores, and the spores often mark a tree's truck underneath the mushroom.

Cross Section

Phellinus <i>robiniae</i>
OrangeRustBrown
The flesh is very wood-like and orange-brown.
Can you Eat Phellinus robiniae?
Inedible
There are some accounts of Phellinus robiniae being used for medicinal purposes, but nothing conclusive. I would highly recommend not consuming this mushroom. It is likely contaminated with pollutants since being perennial and often near populated areas.

Phellinus robiniae Photos

Phellinus robiniae Phellinus robiniae - Black Locust Tree Phellinus robiniae - Cap Surface Texture Phellinus robiniae - Cracked Cap Polypore Phellinus robiniae - Cracked Cap Polypore Phellinus robiniae - Cracked Cap Polypore Phellinus robiniae - Fallen Cap Phellinus robiniae - Fallen Pores Phellinus robiniae - Growth Stage Phellinus robiniae - Growth Stage Phellinus robiniae - Growth Stage Phellinus robiniae - Growth Stage Phellinus robiniae - Growth Stage Phellinus robiniae - Growth Stage Phellinus robiniae - Large Phellinus robiniae - Large Phellinus robiniae - Margins Phellinus robiniae - Margins Phellinus robiniae - Pores Phellinus robiniae - Pores Phellinus robiniae - Recently Fallen Phellinus robiniae - Recently Fallen Phellinus robiniae - Recently Fallen Phellinus robiniae - Recently Fallen Phellinus robiniae - Wet Phellinus robiniae - Wet
Sources