The Collaborative International Dictionary of English v.0.48:

Botanist \Bot"a*nist\, n. [Cf. F. botaniste.]
   One skilled in botany; one versed in the knowledge of plants.
   [1913 Webster]

WordNet (r) 3.0 (2006):

botanist
    n 1: a biologist specializing in the study of plants [syn:
         botanist, phytologist, plant scientist]

Moby Thesaurus II by Grady Ward, 1.0:

27 Moby Thesaurus words for "botanist":
   anatomist, bacteriologist, biochemist, biologist, biometrist,
   biophysicist, bryologist, cytologist, dendrologist, ecologist,
   geneticist, herbalist, mycologist, natural scientist, naturalist,
   physiologist, phytobiologist, phytoecologist, phytogeographer,
   phytographer, phytologist, phytonomist, phytopaleontologist,
   phytopathologist, phytoteratologist, pomologist, zoologist