Stropharia rugosoannulata
Found in April growing from wood debris (sticks, logging chips,
mulch) accumulated along a creek bed.  Spore print: Purple-brown.
The purple-brown spores of Stropharia rugosoannulata.
These spiny cells (called acanthocytes) are mainly associated with the
mycelial threads that can be found at the mushrooms base (see middle
photo at top).  These cells may protect the mycelium from microfauna.  
It has been shown that acanthocytes have the ability to kill nematodes
(microscopic worms).