Bulbous

Bulb with a volva (Highest danger)

M.Ya. Zerova always stressed that a bulb enclosed in a sac (a volva) is the main hallmark of the genus Amanita (amanitas).

- Death cap (Amanita phalloides): It has a pronounced round bulb that sits loosely in a roomy, membranous white sac. This sac is what remains of the universal veil, inside which the mushroom developed as an "egg."

- Panther cap and false death cap: Their bulb is usually fused to the stem and has several concentric rims around its edge (remnants of the volva stuck to the bulb).

If you don't dig away the moss and check the bulb, a death cap will look like an ordinary green brittlegill.

The marginate bulb of webcaps

David Arora describes another type of bulb, typical of the huge and very dangerous genus Cortinarius (webcaps):

Some webcaps have what's called a marginate bulb. It looks as if a straight cylindrical stem had been forced into a wide, flat saucer. The bulb has a distinct, sharp upper edge (the margin). Since some webcaps are deadly poisonous (they destroy the kidneys), a flat bulb like this should be an instant "Stop!" signal for any forager.

Safe bulbs

Of course, not every mushroom with a bulbous stem is poisonous:

1. Violet webcap (Cortinarius violaceus): It has a massive round bulb (but not a marginate one) and is an excellent edible mushroom.

2. Wood mushroom (Agaricus silvicola): Its stem widens abruptly at the base, forming a small bulb (but with no volva sac whatsoever!).

3. Porcini (Boletus edulis): Its stem is often barrel- or pear-shaped, massive and bulbous in young specimens (to support the heavy cap).