Lewis Short
ădarca | ădarce, es (noun F) = ἀδάρκη, ἀδάρκης: and
* A froth or efflorescence deposited on sedge, etc., forming a spongy growth, also called calamochnus; form adarca, Plin. 32, 10, 52, § 140; id. 16, 36, 66, § 167; 20, 22, 88, § 241: form adarce, Veg. 3, 48, 2; 4, 28, 15; Cael. Aur. Tard. 1, 1.
Charlton T. Lewis, Charles Short, A Latin Dictionary