Rules of the Thumb (CWIDT, yo-yo?)
If the head is connected to the stem...it is safe.
If the head is separate from the stem, it is poisonous.
I think that's correct, but I won't stake my life on it.
Before picking morel mushrooms, folks should be aware of what are commonly referred to as true and false morels. Consuming false morels can be dangerous. For example, Gyromitra esculenta, known as the beefsteak morel, has been responsible for many deaths in Europe and several poisonings in the U.S., according to nonprofit organization Midwest American Mycological Information.
Chris Wright, executive director of the organization, said there are a couple of simple ways to tell the difference between true and false morels. True morels are hollow with no materials inside. However, false morels will have a substance that looks similar to cotton, he said. Other than on half-free varieties — on which the cap attaches about halfway down the stem — an edible morel’s stem is attached to the bottom of the cap. With false morels, Wright noted that the stem joins at the top of the cap, with the top folding over like a skirt on top of the stem.