Conferv[ae]

from The Collaborative International Dictionary of English v.0.48

Conferva \Con*fer"va\, n.; pl. {Conferv[ae]}. [L., a kind of
   water plant. See {Comfrey}.] (Bot.)
   Any unbranched, slender, green plant of the fresh-water
   algae. The word is frequently used in a wider sense.
   [1913 Webster]