A single large mushroom whose surface structure is a reaction-diffusion pattern — not decoration applied to a mushroom, but the pattern the organism grew in. The pattern must be generated inside Blender (geometry nodes simulation zones, dynamic paint, or an equivalent iterative process — never hand-painted, never an image texture) and must drive real displacement.

The growth reads upward, as if the pattern expanded as the mushroom grew: near the base of the stem the pattern is sparse — isolated spots and short ridges — and it densifies with height, becoming a fully developed labyrinthine ridge network across the top of the cap. This base-to-cap gradient is the core requirement: one continuous pattern at different stages of its own growth.

Around that patterned surface, the elements that make it a mushroom, all present:

1. A domed cap with the mature reaction-diffusion ridges raised out of its surface.
2. Radial gills on the cap's underside, thin and densely spaced, running from stem to rim.
3. A fibrous stem carrying the sparse early-stage pattern, anchored to a small patch of substrate (soil, moss, or bark) by visible mycelium threads.
4. A fine dusting of spores settled on the substrate beneath the cap's rim.

Materials sell the organism: subsurface scattering in the flesh, a moist look in the gills against a drier, more leathery cap, the ridges slightly darker or more saturated than the valleys between them. Lit softly, like a forest-floor specimen photo — the displacement must be readable in the shading, not flattened away.

The pattern is the exhibit — showcase it to the camera. Frame and pose the shot so the reaction-diffusion surface dominates: the cap angled toward the lens with its labyrinthine ridge network filling a large share of the frame, close enough that individual ridges, their branching, and the base-to-cap density gradient are unmistakable at a glance. Rake the key light low across the ridges so displacement throws real shadows. A viewer who has never heard the words "reaction-diffusion" should still walk away having clearly seen the pattern; if the ridges are too small, too distant, or too softly lit to read, the image has failed regardless of how good the mushroom is.