Eccentric

Why does the stem shift?

As David Arora explains, an eccentric stem is most often the mushroom's response to the spatial conditions it grows in.

A mushroom always tries to hold its cap perfectly horizontal (so the spores can fall freely downward). If it grows on a steep slope, on a leaning tree trunk or at an angle out of a crack in a log, its stem will bend and attach to the cap off-center, compensating for the tilt of the substrate.

Typical species with an eccentric stem

Although eccentricity is often an individual response, for some mushrooms it is the norm for the species:

1. Sawgills (Neolentinus): Large mushrooms that grow on dead wood (especially pine). Their very dense, tough stem is almost always attached to the cap eccentrically. Their gills have finely serrated (saw-toothed) edges, which is their main feature.

2. Oyster mushroom (Pleurotus ostreatus): Although we usually call the oyster mushroom's stem lateral, in young mushrooms or those growing on horizontal surfaces it is often precisely eccentric (the cap grows unevenly around the stem).

3. Dryad's saddle (Cerioporus squamosus): Its large, scaly cap always rests on a thick eccentric (or lateral) stem that blackens at the base.