- The Roberts Rose Company
- Theakston, Michael.
- Theakston, R. David G.
- Theau, Jerome
- Thébaud, Augustus J., 1807-1885
- Thébault, V
- Thébault, Victor, 1866-
- Theberge, John B
- Theberge, Mary T.
- Thedenius, Knut Fredrik, 1814-1894
- Théel, Hjalmar Hjalmar Theel 1848-1937
- Theeler, George C
- Theerakulpisut, P.
- Theidel, Richard.
- Theilade, Ida
- Theile, Friedrich Wilhelm, 1801-1879
- Theiler, Arnold, Sir, 1867-1936
- Theiler, G
- Theiler, Gerardo R.
- Theiler, Karl
- Theiler, Natalia
- Theilmann Seed Co.
- Theimer, Tad C
- Thein, Tin
- Théis, Alexandre-Étienne-Guillaume, baron de
- Theis, Thomas.
- Theischinger, G.
- Theisen, Mark A.
- Theiss, Susan M
- Theißen, Bernhard
- Theissen, Ferdinand, 1877-1919
- Theissinger, Kathrin
- Thejaswi, S.
- Thel, T. N.
- Thelander, Carl G.
- Thelen, Rolf.
- Theler, James L.
- Thélin, L. (Luc)
- Thell, A
- Thellung, Albert, 1881-1928
- Thelohan, Prosper
- Thelot, Jean-Pierre
- Thelot, Johann Andreas, 1655-1734
- Thelott, Johann Philipp, active 17th century-
- Then, Alexander M
- Then, Amy Yee-Hui
- Thenius, Erich
- Thenmozhi, K.
- Theo Burt & Sons.
- Theo. Bechtel (Firm)
- Theo. Koss (Firm)
- Theobald, Charles
- Theobald, Fred. V. (Frederick Vincent), 1868-1930
- Theobald, S
- Theobald, W. (William), 1829-1908
- Theobald, William L.
- Theobaldo de Jesu Maria, Fr.
- Theobold, William
- Theodor de Bry (Firm)
- Theodor, Oskar
- Theodore Payne (Firm)
- Theodore Payne Foundation for Wild Flowers and Native Plants, Incorporated.
- Theodore van Veen Nursery Co.
- Theodore, Jason
- Theodorides, J
- Theodorus, Iacobus, 1590
- Theodosia B. Shepherd Co.
- Theodosia B. Shepherd Company.
- Theodosia B. Sherpherd Co.
- Theodosius Rihelius.
- Theoduloz, Cristina
- Theophrastus.
- Theorin, Gustaf Robert Alfons, 1841-1881
- Theosophical Society (Great Britain)
- Ther, Francisco
- Thera, Trevor, 1971-
- Theresa M. Monmonier (Firm),
- Therese, Princess of Bavaria, 1850-1925
- Thérézien, Y
- Thériot
- Theriot, Edward C
- Thériot, I. (Irénée), 1859-1947
- Theriot, Russell F.
- Therkildson, W. F.
- Theron, A. C. (Albert Christiaan)
- Theron, André
- Theron, J. N.
- Theron, Jacobus Johannes, 1896-
- Theron, Pieter D.
- Therond, Jean
- Theroux, Michael E
- Theroux, Roger B.
- Therres, Glenn D.
- Therrien, James P
- Therrien, Jean-François
- Théry, André, 1864-1947
- Théry, Marc
- Thery, Thomas
- Thesing, Curt, 1879-
- Theska, Tobias
- Thessen, Anne
- Theulegoet, Hynderick de.
- Theuriet, André, 1833-1907
- Theurillat, Jean-Paul
- Théveneau, Antonin Victor, 1814-1876
- Thévenin, Armand
- Thévenin, Armand, 1870-1918
- Thévenin, R.
- Thevenon, Mario Alberto
- Thévenot, Alfonso María
- Thévenot, M
- Thévenot, Melchisédec, 1620-1692
- Thévenot, Michel
- Thew, Thomas B.
- Thewes, M. R.
- Thewissen, J. G. M.
- Thewke, Siegfried E.
- Thewlis, Richard M.
- Thews, J. G.
- Theyensis, Armand
- Thez, A.,
- Thi Kim Thanh, Nguyen
- Thi Thao, Hoang
- Thị Thu Nguyễn, Trang
- Thiagarajan, K. B.
- Thiagarajan, V.
- Thiago, P. S.
- Thiaucourt, François
- Thibaud, J.-M. (Jean-Marc)
- Thibaudeau, Antoine-Claire, comte, 1765-1854
- Thibault, George
- Thibault, Jean-Claude
- Thibault, Marc
- Thibault, Michel
- Thibault, Nicolas,
- Thibaut, George
- Thibaut, M
- Thibo, Karen
- Thibodeau, Francis R., 1953-
- Thickens, J. H. (John Herman)
- Thicknesse, Ralph, 1719-1790
- Thie, Krista K
- Thiébaud, Charles-Henri
- Thiébaud, Maurice
- Thiébaut de Berneaud, Arsenne, 1777-1850
- Thiébaut, Charles
- Thiébaut, Melanie
- Thiede, Joachim
- Thiede, Ulrike
- Thiede, Walther
- Thiel, Jacques van
- Thiel, Martin, 1962-
- Thiel, Ralf
- Thiel, Richard P.
- Thiele, A. O.
- Thiele, Friedrich
- Thiele, Jan
- Thiele, Johannes, 1860-1935
- Thiele, K
- Thiele, K T
- Thiele, Kevin
- Thiele, Kevin
- Thiele, Kevin
- Thiele, Kevin, 1959-
- Thiele, R.
- Thiele, Sabrina Campos
- Thielens, Armand, 1833-1878
- Thiele-Pfeiffer, Heidemarie
- Thiem, H.
- Thiem, Jason
- Thiem, Jason D
- Thiemé, Jardinier decorateur.
- Thieme, Mary S. (Mary Stevenson)
- Thieme, Otto, 1837-1907
- Thien, Leonard B.
- Thienemann, August, 1882-1960
- Thienemann, Friedrich August Ludwig, 1793-1858
- Thienemann, J. (Johannes), 1863-1938
- Thiengo, Marciana
- Thiengo, Silvana
- Thier, R. W.,
- Thier, Tim
- Thieret, John W.
- Thierfelder, Hans, 1858-1930
- Thierriat
- Thierry frères (Firm),
- Thierry-Mieg, Paul
- Thiers, Barbara
- Thiers, Harry D., 1919-
- Thiers, Oscar
- Thiersch, Ernst
- Thiéry de Menonville, Nicolas-Joseph, 1739-1780
- Thiéry, Alain, 1952-
- Thiéry, Maurice.
- Thiéry, P.
- Thies, Conrad W.,
- Thies, Monte L.
- Thiesmeyer, Lincoln R. (Lincoln Reuber), 1908-
- Thiessen, Abraham.
- Thiessen, Jason
- Thiessen, Reinhardt
- Thieuloy, Jean-Pierre
- Thiffault, Evelyne
- Thijs, Ann
- Thilenius, G. (Georg), 1868-1937
- Thilenius, John F.
- Thill, Ronald E.
- Thillot, A.
- Thilo, Johann Gottfried, active 1705-1716
- Thimann, Kenneth Vivian, 1904-1997
- Thimlar, J. Wiley, Dr.
- Thin, Nguyen Nghia
- Thin, Thin
- Thind, Amarinder S
- Thind, B. B.
- Thines, Marco
- Thinh, Luong-Van
- Thinh, N. V.
- Thinon, M
- Thiolat,
- Thiollay, Jean-Marc
- Thiollaz, E. de
- Thiollier, Joseph, 1869-
- Thiolliere, Victor.
- Thiombiano, Adjima
- Thireau, Michel, 1943-
- Thirion, Jean-Marc
- Thiriot-Quievreux, Catherine
- Thirumalachar, M. J.
- Thirumalmnathan, P.
- Thirumurthi, S.
- Thiry, Georges, 1870-1936
- Thiry, Ludwig
- Thiselton-Dyer, William Henry.
- Thiselton-Dyer, William T. (William Turner), 1843-1928
- Thistle, David
- Thistle, Harold.
- Thistleton, Brian M
- Thistlewood, Howard M. A.
- Thite, A. N.
- Thiv, Mike
- Thivy, Francesca
- Thiyagaraja, Vinodhini
- Thiyagesan, K.
- Tho. Warren.
- Thoawan, Kodeeyah
- Thoday, David 1883-1964
- Thode, Verônica Aydos
- Thoenes, Steven C
- Thoeny, William T.