NOTES ON NEOTROPICAL EUPHORBIACEA.E 3. Synopsis of Ca-fibbean Sapium E. Jablonski New York Botanical Garden When working on the Euphorbiaceae of the Guayana Highland I frequently had to extend my studies over the whole of South America. Here I encountered great difficulties >n.th the genus Sapium . The variability of characters, coupled \>rith a lack of morphological discontinuity between the species, made the im-pression of a high plasticity of sub generic taxa and a free flow of genes, probably also combined with a great deal of introgression. Extending my studies subsequently to the Caribbean area I was pleasantly surprised by the decrease of difficulties and the sharpness of morphological boundaries between the species, especially in the West Indies. Although the differences be-tween the individual species remain small and the variability great, the specific limits are better defined and the flow of genes less free. It is interesting to follow Sapium jamaicense from West to East through Cuba, Jamaica, Hispaniola to Porto Rico, where its distribution ends sharply; but before it ends completely it gives rise to a closely related, well defined local species S. laurocerasus . This is not the case when tracing S, jamaicense westward into Central America and southern Mexico. Here S. pleiostachys appears on the scene as a local, closely related species, connected with transitional forms and only acceptable as a separate entity because of the complete lack of this form in the east. It is true that the collections are much more complete in the West Indies than in southern Mexico and Central America, which makes the geographical comparisons less reliable. An interesting feature is the close relationship of the group cuneatuin -leucogynum -haitiense -adenodon -maestrense cubense -moaense -parvifolium and e rythro spe rmum . All endem-ics concentrated in a small area between Jamaica, Cuba Oriente, and the western tip of Haiti, they are characterized by cuneate leaf form, unpronounced submerged lateral nervature and lack of petiolar glands. Although these forms are all closely related, their specific limit is sharp and definite. SapiuJi is confined to the tropics. It hardly crosses the geodetical limits of the Tropics of Cancer and Capricorn. The southern liinit is reached only by xerophytic types, and Dr. 393
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