"The identifying ornamental growths of alpha thallids may be hereditary, or catalyzed by some chemical signal."
—*Sarpadian Empires, vol. III*

Sporecrown Thallid

Each other creature you control that's a Fungus or Saproling gets +1/+1.

Foundations Jumpstart

Dominaria

Because damage remains marked on a creature until it’s removed as the turn ends, nonlethal damage dealt to a Fungus or Saproling creature you control may become lethal if Sporecrown Thallid leaves the battlefield during that turn.

If a creature is somehow both a Fungus and a Saproling, Sporecrown Thallid’s ability gives it only +1/+1.