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In a chemotaxonomic study of the genus Thapsia (Apiaceae), root material of five taxa has been analysed for skin irritating sesquiterpene lactones and the coumarins, 6-methoxy-7-geranyloxycoumarin and scopoletin. Eight tetraesters of 2, 3, 7, 8, 10, 11-hexahydroxy-C (6)-guaianolide and two triesters of 3, 7, 8, 10, 11-pentahydroxy-C (6)-guaianolide were isolated. One of these, trilobolide, has previously been isolated from Laser trilobum Borkh., whereas the others are new. They represent a new group of selective histamine liberators. Regarding the investigated constituents, T. garganica L. was found to differ from T. transtagana Brot. T. villosa L. proved to be chemically heterogeneous and the examined plant samples could be divided into four chemical groups, named I-IV. Hydroxylated C (6)-guaianolides were isolated from T. garganica, T. transtagana, T. maxima Mill., T. villosa I and III. No skin irritating guaianolides were detected in either T. villosa II and IV or in Rouya (Thapsia) polygama (Desf.) Coincy. 6-Methoxy-7-geranyloxycoumarin showed the same distribution as the guaianolides, whereas scopoletin was found in all the plant samples investigated.

Plants used by Guaymi "Curanderos" in Western Panama (Bocas del Toro and Chiriquí) are listed. Results of a literature survey are also reported, including medical use, known constituents and pharmacological effects.