The Collaborative International Dictionary of English v.0.48:

Rubiginose \Ru*big"i*nose`\, Rubiginous \Ru*big"i*nous\, a. [L.
   rubiginosus, fr. rubigo, robigo, rust: cf. F. rubigineux.]
   (Bot.)
   Having the appearance or color of iron rust; rusty-looking.
   [1913 Webster]