Source : Webster's Revised Unabridged Dictionary (1913)

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.

Source : WordNet®

confervae
     See {conferva}

conferva
     n : any of various algae of the genus Tribonema; algae with
         branching filaments that form scum in still or stagnant
         fresh water
     [also: {confervae} (pl)]