The second most important feature of a gilled mushroom is one that you may not think of with most mushrooms: gill attachment. How are the gills attached to the stem, if at all? There are two main categories for gill attachment: free and attached. When we say a mushroom has free gills we mean that the gills never reach over to touch the stem. This is quite noticeable in older mushrooms as there is a small area around the stem where there are no gills. It’s sometimes harder to see in younger mushrooms but still noticeable. The second category, attached gills, is further divided into degrees of attachment: Are the gills just barely attached (adnexed)? Do the gills run straight into the stem (adnate)? Or do the gills run down the stem for a little ways (de-current)? If this weren’t complicated enough, there is one other common possibility where the gills get short like they want to be free, but near the stem are de-current. These are called notched gills.
So how do you keep all of these attachments straight? Most people just divide gill attachment into four possibilities:
Free, Attached, Decurrent or Notched (where it’s understood that attached means not de-current and not notched). One rarely needs a finer distinction.