Hold on there, friend! Even though it shares the name, Morelull and its evolution really don't have a whole lot of similarities with morels. The big problem for me is that they both lack the distinctive ridges on their caps, the things that make morels so famous. I can see the similarities with cantharellus, but their gills don't deviate from the stem, like in Morelull's evolution.
When I first saw them, especially the evolution, they really reminded me of parasol mushrooms. They grow in clusters like the ones on Morelull's head, and furrow out to show their frills once they mature, like in its evolution. They also commonly form fairy rings (hence the Fairy typing), but! Chlorophyllum molybdites are the mushrooms most commonly mistaken for parasol mushrooms, are poisonous, grow in Hawaii, and they have scales on their rounded, flat caps like you can baaaarely see on Morelull's evolution!
I think it's highly likely that its evolution drops its Grass type for Poison, especially since we already have one Grass/Fairy in Tapu Bulu.