The Collaborative International Dictionary of English v.0.48:

Lappaceous \Lap*pa"ceous\ (l[a^]p*p[=a]"sh[u^]s), a. [L.
   lappaceus burlike, fr. lappa a bur.] (Bot.)
   Resembling the capitulum of burdock; covered with forked
   points.
   [1913 Webster]