From The Collaborative International Dictionary of English v.0.48:
Laminaria \Lam`i*na"ri*a\, n. [NL. See Lamina.] (Bot.)
A genus of great seaweeds with long and broad fronds; kelp,
or devil's apron. The fronds commonly grow in clusters, and
are sometimes from thirty to fifty feet in length. See
Illust. of Kelp.