The circumstances surrounding the discovery of this remarkable tree in the mountains of Michoacan, Mexico were published in a popular article by the collector Mr K. W. Beisel (1982). The plant was then thought to belong to the Simaroubaceae, hence the title 'Die aufregende Geschichte vom G6tterbaum' (The exciting story of the Tree of Heaven). A photograph accompanying the article shows the strange appearance of a rooted shoot with the stem covered with thorn-like protuberances and with a flush of pinnate leaves at the top. Mr Beisel, a collector and grower of cacti from Steinfeld, West Germany, first found the plant leafless in February 1979 in a rocky area at 800-1000 m in tropical semi-deciduous forest. The dry season in this region lasts from November to April and during this period many of the trees lose their foliage. When first discovered, the plant appeared to be a succulent growing on a tree but Mr Beisel later realized that what he had seen were, in fact, the young branchlets of the tree. On a further visit in March 1980 (not May 1980 as stated in the above article) further trees were found and many leafless shoots were collected as well as old fruits and what appeared to be seeds. Mr Beisel in West Germany and others in California and Zurich succeeded in rooting the live shoots and germinating the 'seeds'. As a result, living plants are at present flourishing in cultivation. Most fortunately, in the Stiidtische Sukkulenten-Sammlung at Zurich both male and female plants have flowered, the male (no. 82-3958) since 1985 and one female (no. 823956) since 1986. These plants were grown from cuttings collected by Mr A. Lau, jr. from the type-locality in 1982. Another female plant produced fruits in July 1987; this was derived from a cutting which was part of Mr Beisel's original collection of 1980. We are greatly indebted to the Director, Mr D. J. Supthut, for sending the flowering and fruiting material which has been essential for this study. At Mr Beisel's request, Mr Supthut sent a living specimen to Mr Gordon Rowley, the well-known expert on succulents, for his opinion of its identity and Mr Rowley subsequently very kindly presented it to Kew (Entry no. 346-87.02502) (Figs. 1 & 2). When received in the winter of 1984-85, the plant consisted of a bare leafless shoot looking completely lifeless, but kept in a warm sunny position and watered sparingly it sprouted leaves in May 1986. After dropping most of its leaves the following winter the plant made good growth during the summer of 1986 allowing observation of the development from the petiole-bases of the pointed protuberances on the