C. nigra comes nearest to C. espinosae Lloyd, but differs from it in colour, internal fibres and shape of apothecia. Both species have a smell resembling apricots. Galls of C. nigra resemble those of C. harioti. Sporophores of C. nigra occur about the same time as those of C. gunnii; the first shedding of spores in 1946 was noted on October 10. The galls are distinguished from those of C. gunnii by their large size in relation to the diameter of the host stem, and their greater height in proportion to diameter. One sapling of 3 in d.b.h. had a gall at 8ft from the ground, 30 in in circumference and 7 in high, completely encircling the stem. This was separated by only 2 in from another, 26 in in circumference and encircling the stem except for a space of 1 in.

Relatively larger galls are found on larger trees; galls of 3ft or more in diameter are frequent. Where the upper part of the attacked tree or branch dies, globose galls of a foot or more in diameter are common.

When the bark is removed the gall is seen to differ from C. gunnii in that the spines are very short and less numerous, they arise from bluntly rounded projections on the surface of the gall. The scar left when the fructification falls is orange in colour and may retain the orange cartilaginous tube from the stroma.