Mela*no*sper"mous

from The Collaborative International Dictionary of English v.0.48

Melanosperm \Me*lan"o*sperm\, n. [Gr. me`las, me`lanos, black +
   spe`rma seed.] (Bot.)
   An alga of any kind that produces blackish spores, or seed
   dust. The melanosperms include the rockweeds and all kinds of
   kelp. -- {Mel`a*no*sper"mous}, a.
   [1913 Webster]