I've been watching Fullmetal Alchemist: Brotherhood lately and noticed that Ed and Al tend to only transmute rock and metal, especially in battle. The same is true of Alex Louis Armstrong. Roy Mustang, of course, works with fire, which is energy (and thus technically inorganic). Even Solf J. Kimblee only seems to transmute rocks and metals.
The more I thought about it, the more I realized that we don't see people transmuting organic materials -- flowers, wood, gems, etc. The only time I can recall seeing a flower be transmuted was in Liore, when the pastor did so. Of course:
He had a philosopher's stone from Father.
Are these materials not transmutable?