There are two places to record mushroom sightings and research the data that others have entered.
The first is http://theopolis.juju.org/shroomdar/, which has not been updated with the new mushroom types (Tokra will probably add the new ones after coming back from illness. ~Wikt).
The second is http://atitd.lr2.com/mushrooms/, which was created by Hodhr and is up-to-date with all of the mushroom types. (Hodhr's tracker is back at a slightly different URL.)