Inky caps are often easy to recognize once they mature, since, perhaps because their gills may be too close together to allow the spores to be ejected, the black spored gills will often deliquesce and turn to ink from the outside edge inward, until only a stem might remain. Species that don't turn to ink have strongly pleated caps from being very thin-fleshed. You can actually fill a fountain pen with the "ink" and write with it. Many of these species are edible, and some people actually eat Coprinus comatus ink. This process can take place anywhere from a few hours to a few days into the life of the mushroom, which means that they need to be eaten quickly after being found. However, 30 seconds or so in a microwave is said to kill the enzyme that causes them to turn to ink allowing you to store them for longer. This may work for Coprinus comatus, but the others are too small and will just turn into a soggy mess.
Inky caps are recognized by dry caps, gills free or almost so and crowded together, black spores, and sometimes an umbrella shaped cap that is taller than it is wide. A universal veil often leaves granular or floccular material on the cap, which is typically not hygrophanous. They are all saprophytic. Most have caps that are strongly striate. Coprinus (related to Agaricus) is the only genus with a ring, but in those related to Psathyrella, the cap cuticles are cellular, meaning that they are very fragile and can break easily in any direction.
1. Coprinus comatus - "Shaggy Mane", recognized by having a large cap much taller than it is wide and being shaggy, not just scaly. A string runs through the hollow stem. The only species with a partial veil (leaving a movable ring on the stem). Remarkably, Coprinus is related to Agaricus. The rest actually evolved independently and are related to Psathyrella.
Other rare species of Coprinus exist. Coprinus comatus var. parvus (caprimammilatus) differs microscopically, Coprinus comatus var. excentricus has larger spores. C. colosseus is huge and has even larger spores. C. asterophoroides and C. xerophilus are small shaggy manes in deserts. C. umbrinus, C. spadiceisporus and C. roseistipitatus are miniature shaggy manes found on dung and C. palmeranus (if distinct from C. roseistipitatus) is a miniature shaggy mane in grass and disturbed areas. None are known to have been photographed, but most are backed up by DNA sequences.
2. Coprinopsis - usually white to greyish caps (instead of brown), often with shaggy or scaly velar material on the cap (or if not, will be especially large (>5cm) or especially minuscule (<1cm), and usually striate. This genus usually completely deliquesces. Found on the ground, wood, or sometimes dung.
One species group contains Coprine, the active ingredient in Antabuse. If you eat this mushroom either a few days before or after consuming alcohol, you will get sick, as Coprine will interfere with the body's ability to process the toxins in the alcohol. Another group, the C. lagopus grp, is so short lived you have to be in the right place at the right time to see it during the only few hours a year it will fruit. Fortunately it is incredibly common, and you will find it at least in its inky state all the time.
Alcohol inky caps
C. striata (pinguispora/
C. strossmayeri - similar, covered in white scales, not containing coprine.
C. lagopus grp - very short lived, copious shaggy velar material on cap. Grey. Ground or burnt ground. <5cm. Includes C. brunneistragulata, C. pachyderma and C. tectispora.
C. cinerea (Coprinus fimetarius) - similar, on dung, <5cm cap height.
Coprinopsis picacea - a large, spectacularly mottled inky cap, with large, off white removable scales. This famous species was only recently discovered in the PNW.
C. friesii - purple grey, in grass, does not deliquesce as much as C. lagopus. Velar material on the cap. Small, cap <1.5cm tall.
C. subdomestica - kind of a cross between Coprinopsis lagopus and Coprinellus flocculosus, with a warm brown and grey cap covered in thick veil material.
Other rare species exist, little known and never photographed.
C. undulata - on compost
C. sylvicola - red-brown veil material on cap
Coprinus alnivorus - a ring, easily mistaken for a small Coprinus.
3. Coprinellus/Tulosesus/Parasola - usually brownish (at least when young) instead of grey. Strongly striate. Caps usually between 1-5cm and may have granular particles, but only rarely (in the PNW) shaggy or scaly velar material like Coprinopsis. Some species do not liquify. Found on the ground, wood, or sometimes dung (see Coprinopsis for white or tiny dung species).
C. micaceus - glistening mica-like particles on a yellow-brown cap <4cm high (larger than the others). The particles wash off easily. Browner in age than Parasola and T. impatiens.
C. saccharinus - similar, but supposedly without any miniature pale hairs on the stem.
C. domesticus group - larger particles that resist wearing off, orange felty mat sometimes in the substrate.
T. ephemerus /congregatus - on dung. <2.5cm
T. heterosetulosus - very tiny on dung. Brownish.