Perichaetium

from The Collaborative International Dictionary of English v.0.48

Perichaetium \Per`i*chae"ti*um\, n.; pl. {Perichaetia}. [NL.,
   fr. Gr. about + ? flowing hair, foliage.] (Bot.)
   Same as {Perich[ae]th}.
   [1913 Webster]