Large, tall and upright with a cylindrical, white and fleecy cap which becomes black from the bottom upwards, the Shaggy Inkcap (Coprinus comatus) should be easy to identify.
They may grow singularly, but usually in small groups, and prefer to grow in grassland, but they are quite happy alongside footpaths, on waste ground or even bare or disturbed soil especially containing woody debris. So the New Forest is a good habitat for them and their often prolific fruit bodies are most likely to appear from April through to November.
The stem is hollow and about 15cm tall with a mobile or free ring, which few fungi possess, near the base. The shaggy cap is torpedo shaped which is widest at the base, and conceals a slender white stem when immature. The crowded gills underneath the cap are white at first, but quickly become black as the fruit body deliquesces (dissolves or auto digests) upwards from the bottom edge of the cap, as it breaks down into a black slimy fluid full of fungal spores. This liquefying aids the important dispersal of the spores.
In the 17th and 18th centuries this black liquid could be used as an ink substitute. It could be used straight as writing ink or in a more concentrated form by boiling down with phenol as a preservative. It was even suggested that it could be used for important legal documents and bank notes, as the absence of any fungal spores would indicate a forgery.
The Shaggy Inkcap can is also often called Lawyer’s Wig (because of its tiers of shaggy white scales akin to a lawyer’s wig) or maybe Shaggy Mane Inkcap.