[1] Basidiocarps (fruit bodies) are agaricoid, with a conspicuous veil (leaving a double ring on the stem), adnate to decurrent lamellae, and amyloid basidiospores.

in 1922 the Austrian botanist Günther Beck von Mannagetta und Lerchenau referred the European species Armillaria imperialis to his new genus Biannularia.

[1] Lovejoy's original description states that:[5] "The ring and volva, together with the very decided decurrent gills (upon which character the generic name is based), are telling characteristics of this genus.

"According to Genaust's etymological dictionary of botanical names, "Catathelasma" comes from Ancient Greek words "kata" (κατά - downwards) and "thelasma" (θήλασμα - meaning "the act of suckling").

He says that the reason for this construction is unclear, but suggests that the author is comparing the shape made by the gills running down the stem with a teat stretched out during suckling.