Thonner's analytical key to the families of flowering plants

For the identification of a flowering plant the first step usually is to discover to which family it belongs. With some experience, the families commonly encountered in one's area of interest are soon known, but when dealing with specimens from other places, notably those from the vast and rich subtropics and tropics, there is much less certainty. The pertinent literature is often not readily available as it is often found only in expensive, rare or obscure books, or journals, present only in a few specialized institutes. Basically only a few keys to the families of flowering plants of the world have ever been produced, the best known of which at present is Hutchinson's Key to the families of flowering plants (1973); less well-known are Lemee's Tableau analytique des genres monocotyledones (1941) (incl. Gymnosperms) and his Tableau analytique des genres dicotyledones (1943), and Hansen and Rahn's Determination of Angiosperm families by means of a punched-card system (Dansk Bot. Ark. 26, 1969, with additions and corrections in Bot. Tidsskr. 67, 1972, 152-153, and Ibid. 74 1979, 177-178). Of note also are Davies and Cullen's The identification of flowering plant families, 2nd ed. (1979), which, however, deals only with the families native or cultivated in North Temperate regions, and Joly's Chaves de identifi~iio das familias de plantas vasculares que ocorrem no Brasil, 3rd ed. (1977), which may be useful in other tropical areas too.