The Collaborative International Dictionary of English v.0.48:

Amaranthus \Am`a*ran"thus\ ([a^]m`[.a]*r[a^]n"th[u^]s),
Amarantus \Am`a*ran"tus\ ([a^]m`[.a]*r[a^]n"t[u^]s), n.
   Same as Amaranth.
   [1913 Webster]