- nucleus
- nucule
- nopal
- nostoc
- nude
- nut
- nut-tree
- nutation
- nutmeg-tree
- oak
- oak-gall
- oak-nut
- nutate
- oak-apple
- oak-fig
- oat
- obconical
- offshoot
- octamerous
- okra
- oleaster
- oil-nut
- onion-couch
- onion twitch
- onion-grass
- oppositifoliate
- oppositifolious
- obcordate
- oblique
- obverse
- obvolute
- odontoglossum
- oleander
- olive
- orange lily
- orbiculate
- orchid
- orchidaceous
- orchis
- order
- origan
- orleans
- orris
- osmundacae
- origanum
- orpin
- orpine
- orthostichy
- orthotropism
- orthotropous
- osier
- osmund
- ovular
- ovule
- oxalis
- oxyacanthous
- oxycarpous
- pagoda-tree
- palmate
- palmatisect
- ovarian
- ovary
- ox-eye
- oxalidaceac
- oxtongue
- pachouli
- pachypleurous
- palm
- palmaceous
- palmetto
- pandanaceae
- panic
- panicle
- pansy
- paeony
- palm-tree
- palma christi
- palmated
- palmettos
- palmyra
- pappose
- pappus
- parallelodrome
- paniculate
- panicum
- papaveraceous
- papper-grass
- paraguay
- paraphyses
- paraphysis
- parasolpine
- paratonic
- parietal
- parsley
- parsnip
- parthenocarpy
- partite
- pasque-flower
- pass
- passion-flower