- Oklahoma Museum of Natural History (Norman, Okla.)
- Oklahoma State Livestock Registry Board.
- Oklahoma. Department of Wildlife Conservation.
- Oklahoma. State Board of Agriculture,
- Okland, Fridthjof
- Okoda, Yô K
- Okolodkov, I︠U︡riĭ B
- Okoniewski, J C
- Okoni-Williams, Arnold
- Okoshi, Kenji
- Okoyama, S
- Oksnebjerg, B
- Oktaviyani, Selvia
- Oktay, H Imge
- Oku, Johei
- Okuda, Hélio T.
- Okuda, Kazuo
- Okuda, Kyosuke
- Okuda, Takashi
- Okulitch, Vladimir J. 1906-
- Okuly, Mallory
- Okum, Sarah
- Okuma, Jiro
- Okumoto, Naoto
- Okumura, George T.,
- Okumura, Ken-Ichi
- Okumura, Takuji
- Okuno, J
- Okuno, Junji
- Okuno, Makoto
- Okura, Nobuhiko
- Okushima, Yûichi
- Okusu, Akiko
- Okutaner, Atılay Yağmur
- Okutani, Takashi
- Okuthe, Grace E.
- Okwany, Zedekiah A
- Okyar, Zühal
- Olabarria, C
- Olabarria, Celia
- Olabuenaga, Susana E.
- Olaciregui, Christian
- Olaciregui, Christian A
- Oladipo, Segun Olayinka
- Olaf J. Wingren (Firm)
- Olafsdottir, Steinunn Hilma
- Olague Ramirez, Jesús
- Oláh, János
- Olajuyigbe, O O
- Olajuyigbe, O. O.
- Olalde Portugal, V
- Olalde, V
- OlalekanAdebiyi Abdul-Hakeem
- Olalla, A. M.
- Olander, C. P.
- Olaniyi, Ajibola A.
- Olariaga, I
- Olariu, Tudor-Sebastian
- Olarte, Luis G.
- Olarte-Castillo, Ximena A.
- Olasagasti, Lander
- Olaus, Magnus, Archbishop of Uppsala, 1490-1557
- Olavarría, Carlos
- Olave, Anabel
- Olave, Carlos
- Olaverri-Monreal, Cristina
- Olavo, George
- Olaya Restrepo, Julián
- Olazarri, Jose
- Olazarri, José
- Olbers, W. 1758-1840
- Olbrich, E. R.
- Olbrych, Katarzyna
- Olcott, Henry Steel, 1832-1907
- Old Baldy Nurseries.
- Old Bee-keeper
- Old bushman, 1815-1865
- Old Calabar.
- Old Cambridge Shakespeare Assoc.
- Old Capital Nurseries.
- Old club, Detroit.
- Old Colony Gardens,
- Old Colony Nurseries.
- Old Colony Nursery.
- Old Dominion Gardens.
- Old Dominion Nurseries.
- Old Dominion University. Dept. of Biological Sciences.
- Old English Nursery.
- Old Fort Camellia And Azalea Nursery,
- Old Guard, pseud.
- Old House Gardens.
- Old Kent Nursery.
- Old Line Cactus Company,
- Old Orchard Gardens (Webster Groves, Mo.)
- Old Orchard Gardens.
- Old Rose Nursery.
- Old Seed House.
- Old Shekarry.
- Old Spanish Trail Orchard and Nursery.
- Old Town Nurseries.
- Old Trail Dahlia Gardens.
- Old West Regional Commission.
- Old, Julie M.
- Old, K M
- Old, Kenneth Malcom
- Old, Richard R
- Old, William E. Jr.
- Oldaker, Frank
- Oldani, Norberto
- Oldani, Norberto Oscar
- Oldberg, Rudolf, 1850-1898
- Olde, P M
- Olde, Peter Maurice
- Oldekop, G
- Oldeland, Jens
- Oldeman, Roelof A A
- Oldemeyer, John. L.
- Olden Nursery Co.
- Olden, G A
- Olden, Julian
- Oldenberg, L
- Oldenberg, Lorenz
- Oldenbourg, R.
- Oldenburg (Germany)
- Oldenburg, Henry, 1615-1677
- Oldenburg, Lorentz
- Oldenburg, R.
- Oldenburger, F H F
- Oldendorp, C. G. A. (Christian Georg Andreas), 1721-1787
- Oldenland, Henrik Bernard, approximately 1663-1697
- Old-Fashioned Gardens.
- Oldfield, R. A. K.
- Oldfield, Ron
- Oldfield, S.
- Oldfield, S., WCMC
- Oldfield, Sara
- Old-Growth Definition Task Group.
- Oldham, Charles
- Oldham, Jonathan A
- Oldham, Michael J.
- Oldham, R D
- Oldham, Ray
- Oldham, Thomas
- Oldham, Timothy C B
- Oldham, W.
- Oldham, William Fitzjames, 1854-1937
- Oldman River Dam Project (Alta.)
- Oldoni, Damiano
- Oldrini, Barbara B.
- Oldroyd, Harold
- Oldroyd, I S
- Oldroyd, T S
- Oldryod, H
- Olds & Whipple, Inc.
- Olds & Whipple.
- Olds College.
- Olds, Brett P.
- Olds, Emily J
- Olds, Fred A.
- Olds, Gary
- Olds, H W
- Olds, L. L.
- Olds, Nancy.
- Oldt, Frank
- Oldtown Nursery,
- Oldys
- Oldys, Henry
- Oldys, Henry,
- Oldys, Henry, 1859-1925
- Oldys, Henry.
- Oldys, May M.
- Olea, Danai
- Olea, Gabriela. B.
- Olea, P P
- Olea, Sofía M.
- Olea-De-La-Cruz Francis Giovani
- Olearius, Adam, 1603-1671
- O'leary, E P
- O'leary, James W
- O'leary, John F
- O'leary, M
- O'Leary, M C
- O'Leary, Mary Adeline
- O'Leary, Maureen A.
- O'Leary, Michael
- O'leary, Michael J
- O'Leary, Nataly
- O'Leary, Nataly
- O'Leary, Ruth, 1973-
- O'Leary,Mary Adeline Sister
- Oleas, Nora
- Olea-Wagner, Alinka
- Olech, Lillian A.
- Olech, Lillian Ann.
- Olędrzyńska, Natalia
- Oleinik, A O
- Oleinik, Anton
- Oleiro, T.A.
- Olejniczak, Paweł
- Olendorff, R R
- Olendorff, Richard R.
- Olendorff, Richard R.,
- Olenick, Roberta J.
- Olenin, Sergej
- Olenwood Gardens Nursery,
- Olenzek, Amy M
- Olert, J
- Oles, Andrew J.
- Olesen, J
- Olesen, J M
- Olesen, Jens M.
- Olesen, Jens Mogens
- Olesen, Jørgen
- Olet, Eunice Apio
- Olexia, P.D.
- Oleyar, M D
- Olfers, I. F. M. Von (Ignaz Franz Maria von), 1793-1872
- Olfert, O
- Olff, Han
- Olgeirson, Erik
- Olguín, Eugenia J.
- Olguín, Laura
- Olguín, Nicole
- Olguín-Hernández, Licet
- Olgun, A
- Olgun, Kurtuluş
- Olhoeft, G. R.
- Oliarinony, Ranalison
- Oliarnyk, Catherine J
- Olibrio, Francesco
- Olifiers, N.
- Olifiers, Natalie
- Olimpio De Souza, Antonio
- Olímpio, Ana P. M.
- Olímpio, Ana Priscila Medeiros
- Olímpio, FMP.
- Olin Corporation. Winchester Western Division.
- Olin, John
- Olina, Giovanni Pietro, active 1622-
- Olinda, RA.
- Olinger, Charles T.
- Olioso, Georges
- Oliphant, George Henry Hewit.
- Oliphant, George Henry Hewitt.
- Oliphant, L W
- Oliszewski, Nurit
- Olita, Antonio
- Oliva Paterna, Francisco J
- Oliva, Adriana
- Oliva, Adriana