Universal veilsAs mentioned in the first article, on the species concept, some mushrooms start out life completely enclosed in a membrane called a universal veil. This is thought to help the fungus to maintain the proper humidity and temperature for the developing mushroom. The universal veil is sort of like a soft eggshell – it can be peeled away without damaging the embryonic mushroom inside. When the mushroom’s stalk starts to expand, it breaks out of the universal veil and keeps on going. Sometimes, you can even catch it in the act, as in the photo to the right.
But most of us don’t sit in the forest watching mushrooms break out of their universal veil, nor do we find the mushroom during those precise few hours where the mushroom is in the act of breaking out. So most of us infer its presence by seeing the remnants left behind after the breakout happens. There are two major places to examine the mushroom for these remains. One is the base of the stalk. Sometimes you can find the lower portion of the eggshell still sitting there, forming a sort of cup.
The other place to look is the surface of the cap. If some of the universal veil stays on the cap, it doesn’t expand as the cap grows, so it usually gets pulled apart into flakes by the expanding cap. Often they are closer together at the center, which doesn’t expand so much; and they get pulled into smaller pieces at the edge, which expands the most. But sometimes they’re also pretty random.
Other mushrooms may end up with a volval patch on the cap, where the cap’s universal veil tissue stays all in one piece in the center.
The consistency of the veil has a bearing on what sort of fragments are left after the veil is broken. Sometimes the universal veil is very crumbly, and the only thing left of it will be a powdery layer or a few flakes on the cap or at the base of the stalk.
Some mushrooms have a slimy universal veil. Mushrooms do not secrete slime the way some animals do, where there are specialized glands that pump slime out. Mushroom slime is formed when hyphae dissolve their cell walls turning their own bodies into mush. Many mushrooms that grow in cold weather or cold locations have a slimy partial veil or universal veil. The general wisdom at this point is that the slime layer acts as an insulator, protecting these mushrooms from the cold.
At the other end of the spectrum, if the universal veil is thick and hard, it may end up forming big chunks or pointy chips on the top of the cap.
There are also different manifestations at the other end of the mushroom. While the sack-like cup (called a volva) at the base of the stalk is the classic indicator of a universal veil, it is not the only one. First of all, the cup may collapse against the stem and become plastered to it. If you don’t know to look for it, it may escape your notice. This kind of volva is called strangulated. As the stem grows, it can pull this sort of volva apart, into zig-zaggy bands on the stem; these are known as strangulated zones.
Likewise, in mushrooms where the thick universal veil forms big chunks or pointy chips on the cap, it may do the same at the base of the stalk also.
There are some groups of mushrooms where the universal veil is an underappreciated feature – many inky caps, for example, have a universal veil that breaks up to give the cap a characteristic texture; but because it is usually portrayed as a cap texture feature, we don’t end up with the correct species concept that this is a mushroom with a universal veil. Likewise, there are quite a few little dark-spored mushrooms that have a universal veil, but it is fragile and light, and easily lost to rain or other weathering – plus, although they are beautiful little mushrooms, only a specialist is likely to try identifying them to species anyway.
It is worth repeating that the universal veil (especially on the cap) can be easily lost to rain or other weathering events. I have emphasized the mushrooms with powdery or fragile veils above, but even a universal veil that seems quite sturdy can be washed away by surprisingly light rain. So don’t assume that just because you don’t see universal veil remnants, there wasn’t one. You have to be a mushroom detective sometimes, and consider evidence even for things that are no longer there.