- O & M Seed Company.
- O. & C. (Firm)
- O. Dickinson Seed Co.
- O. E. Spencer (Firm)
- O. H. White & Son.
- O. Kenneth Smith (Firm),
- O. M. Oudyk (Firm)
- O. Machholz (Firm)
- O. Machholz Seed Co.
- O. P. Fogle (Firm)
- O. R. Gottwold (Firm)
- O. S. Gray Nursery & Landscape,
- O. W. Rich Nursery.
- O., J. L.
- O., W. S.
- O.A. Risk (Firm)
- O.A.D. Baldwin (Firm)
- O.A.D. Baldwin Nursery Co.
- O.A.D. Baldwin Nursery.
- O.A.E. Baldwin (Firm)
- O.C. Waller & Brothers.
- O.C. Waller (Firm)
- O.D. Shields & Co.
- O.F. Garrett (Firm),
- O.F. Marvin (Firm)
- O.F. Marvin (Firm).
- O.H. Palm Seed Co.
- O.H. Perry Nursery Co.
- O.H. White & Son.
- O.J. Barnes (Firm)
- O.J. Barnes Seed Co.
- O.K. Nursery.
- O.K. Seed Store.
- O.L. Giese (Firm)
- O.L. Ringle (Firm)
- O.L. Weeks (Nursery),
- O.M. Jowers (Firm)
- O.M. Pudor (Firm)
- O.M. Richardson & Co.
- O.M. Scott & Sons Co.
- O.M. Scott & Sons.
- O.P. Conklin (Firm)
- O.P. Fogle (Firm)
- O.P. Jackson & Company, Inc.
- O.P. Jackson Seed Co., Inc.
- O.R. Howe, Jr. (Firm),
- O.R. Roe Glads,
- O.S. Gray Nursery,
- O.S. Gray Pecan Nursery.
- O.S. Jones & Co.
- O.S. Jones Seed Co.
- O.S.T. Orchard and Nursery Experiment Station.
- O.T. Louis Co.,
- O.V. Zangen (Firm)
- O.W. Clark & Son.
- O.W. Conner (Firm)
- O.W. Hoke (Firm)
- O.W. West (Firm)
- O’Brien, Aidan M.
- O’Brien, Gavin
- O’Connor, D.
- O’Connor, Katie
- O’donnell, Charles James
- O’riley, E
- O’shaughnessy, William Brooke
- O2 Planning + Design Inc.
- Oak Dale Berry Farm.
- Oak Grove Fruit Farm.
- Oak Grove Nursery.
- Oak Hill Nursery (New Buffalo, Mich.)
- Oak Hill Nursery (Washburn, Tenn.)
- Oak Knoll Garden Center,
- Oak Knoll Gardens.
- Oak Lawn Nursery.
- Oak Leaf Nurseries and Apiaries.
- Oak Mound Nursery.
- Oak Park Nurseries (East Patchogue, N.Y.)
- Oak Ridge National Laboratory.
- Oak Ridge pecan company.
- Oak, Dorothy
- Oakdale Farm.
- Oakdell Nurseries And Greenhouses,
- Oakeley, Henry
- Oakes Ames Orchid Herbarium
- Oakes Nursery (Oakes, N.D.)
- Oakes, A. J.
- Oakes, Wayne
- Oakes, William, 1799-1848
- Oakey, Jane
- Oakhurst Gardens.
- Oakhurst Nurseries.
- Oakland Dahlia Gardens.
- Oakland Greenhouses.
- Oakland Green-Houses.
- Oakland Nurseries (Columbia, Tenn.)
- Oakland Nursery Co. (Columbia, Tenn.)
- Oakleaf, R
- Oakleigh Gardens.
- Oakley Hill Bulb Company.
- Oakley Nurseries.
- Oakley, Arthur L.
- Oakley, Kenneth Page
- Oakley, Luis
- Oakley, Luis J
- Oakley, R G
- Oakley, R. A. (Russell Arthur)
- Oakley, S M
- Oakley, T. L.,
- Oakley-Pate Seed Co.
- Oakley-Pate Seed Company.
- Oaks, John A
- Oakside Dahlia Gardens.
- Oakside Gardens.
- Oakwood Farms
- Oami, Kazunori
- Oana Paula, Popa
- Oancey, P A
- Oanh, Nguyen Thi
- Oar, J
- Oasis Nurseries (Colombo, Sri Lanka)
- Oates, Brian
- Oates, Charles George.
- Oates, Eugene W
- Oates, Eugene William, 1845-1911
- Oates, F.
- Oates, Frank
- Oates, Frank.
- Oates, G G Thompson& J E
- Oates, John F., 1944-
- Oates, John F., 1944- 1944-
- Oates, M
- Oates, Max Bruce, 1883-
- Oates, Robert Washington
- Oatley, Terry
- Oatman, E R
- Oatman, G F
- Oats, Frank.
- Oba komitéty pro přirodovědecký výzkum země České.
- Oba, Yuichi
- Obac, AR.
- Obalski, T
- Obando, Lenin A
- Obando-Pereda, GA.
- Obar, Robert
- Obara, A. T.
- Obara, AT.
- O'Bara, Christopher J.
- Obara, Yoshitaka
- Obata, Chizuko
- Oba-Yoshioka Eliane Tie
- Obbard, James
- Obbard, Martyn E.
- Obbens, F
- Obbens, F J
- Obbens, Frank J
- Obbinson, R.
- Obed, Yamila S.
- Obedzinski, R. A.
- Obee, E M
- Obein, Gaël
- Obenat, Sandra
- Obenberger, J
- Obenberger, Jan
- Obenchain, Jeannette Brown.
- Obendorf, D L
- Ober, Frederick A. (Frederick Albion), 1849-1913
- Ober, Karen
- Ober, Lewis D.
- Oberbauer, Thomas A
- Oberdorff, Thierry
- Oberg, Erik T
- Oberhauser, Karen S. (Karen Suzanne)
- Oberhessische Gesellschaft für Natur- und Heilkunde, Giessen.
- Oberhollenzer, H.
- Oberholser, Harry C.
- Oberholser, Harry C. (Harry Church), 1870-1963
- Oberlin Peony Gardens,
- Oberlin Peony Gardens.
- Oberlin, R. L.
- Oberlin, Reuben L.
- Oberlin, Thomas J.
- Oberlin, Thos. J.
- Oberling, J-J
- Oberling, John J
- Oberly, Eunice Rockwood, 1878-1921
- Obermayer, Walter
- Obermeyer, B K
- Obermeyer, Kim E.
- Oberndorfer, R Y
- Oberndorfer, Rudolf
- Oberprieler, Rolf G
- Oberprieler, Stefanie K
- Oberski, Jill
- Oberst, Eneder Rosana
- Oberst, George.
- Oberst, M
- Obersteiner, Heinrich
- Oberthür, C
- Oberthür, Charles
- Oberthür, Charles, 1845-1924
- Oberthur, R
- Oberthür, René.
- Oberto, Ana M
- Oberto, Ana M.
- Obert's Dahlia Gardens.
- Oberwimmer, Alfred
- Obeso, José Ramón
- Obeso-Huerta, Hipólito
- Obeso-Huerta, Hipolyto
- Obeso-Nieblas, Maclovio
- Obika, Masataka
- Obin, Martin S
- Obinata, Takashi
- Oblad, Briant R. 1940-1993
- Obolensky, George,
- Obón, Concepción
- Obona, Jozef
- Obonyo, Julius
- Oborny, Adolf.
- Obourn, Ellsworth Scott, 1897-
- Obourn, T H
- Oboussier, Henriette
- Oboyski, Peter
- Oboyski, Peter T
- Obraztsov, N
- Obraztsov, Nikolaus S., 1906-
- Obrecht, Alberto
- Obrecht, E
- Obrecht, Rufus C. (Rufus Chancey), 1875-
- Obregon, Frank
- Obregon, Ignacio de
- Obreque, Cecilia
- Obreque, Víctor
- Obreshkove, Vasil
- O'Brian Forest Nursery.
- O'brian, Dennis M
- O'Brien Aquatic Gardens.
- O'Brien, A. H. (Arthur Henry), 1865-1957
- O'brien, B R A
- O'brien, Bart
- O'brien, Bart C
- Obrien, C
- Obrien, C W
- O'brien, C W
- O'brien, Charles W
- O'brien, D P
- O'Brien, Deborah Mayer.
- O'Brien, E.
- O'Brien, E., Lt.-Col.
- O'Brien, Edward J., 1939-