Among his many contributions to taxonomy are his treatments of the Medusagynaceae, Theaceae, Violaceae, and Canellaceae for the second edition of the Die Natürlichen Pflanzenfamilien of Engler & K. Prantl, the publication as editor with E. Werdermann, of ed.
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His main interest was in the Violaceae, Theaceae, and Bignoniaceae and, especially in his earlier years, in the flora of the Alps.
Hans Christian Andersen | Hans Holbein the Younger | Hans Zimmer | Hans Werner Henze | Hans Memling | Hans Pfitzner | Hans Küng | Hans Conried | Hans Knappertsbusch | Hans Magnus Enzensberger | Hans-Dietrich Genscher | Hans Blix | Hans Zender | Hans Scholl | Hans Hofmann | Hans Christian Ørsted | Hans Raj Hans | Hans Habe | Hans Baldung | Baron Hans Heinrich Thyssen-Bornemisza | Hans von Ohain | Hans van Manen | Hans Urs von Balthasar | Hans Sloane | Hans Rosbaud | Hans-Georg Backhaus | Hans-Adam II, Prince of Liechtenstein | Yuvraj Hans | Hans von Halban | Hans von Bülow |