Orpine. See [Sedum].
Osage Orange. See [Maclura].
Osier. See [Salix] and [Cornus].
Osmanthus (Japan Holly). Oleaceæ.
Propagated by cuttings under glass, or by grafting on osmanthus stock, or on privet.
Osmunda (Flowering Fern). Filices.
Mostly by division; sometimes by spores. See [Ferns].
Ostrya (Hop Hornbeam, Ironwood). Cupuliferæ.
Best grown from seeds. Also increased by layering; or it can be grafted. The European species is often grafted upon the hornbeam (carpinus).
Othonna, Aristotela, including Doria (Ragwort). Compositæ.