Abstract
Tubiflorae sensu Wettstein (1935) and sensu Melchior (1964, in Engler's Syllabus) are a rich source of iridoid compounds. Steamvolatile constituents (like I and II in fig. 1), iridoid glycosides (like III to X in fig. 1) and simple monoterpenoid alkaloids (like XI–XV in fig. 1) occur in many taxa. Their occurrence in all families mentioned in table I is described and many unpublished observations (marked with an asterisk * in tables II–VII) are reported. In many instances iridoid metabolism is a character worthwhile to be seriously considered by those plant taxonomists which are interested in a natural classification of the Dicotyledons. Many examples showing the usefulness of iridoid compounds to plant systematics are shortly discussed. At the same time many iridoid glycosides and closely related constituents must be considered to be biologically very active plant constituents. They deserve the attention of many branches of medicinal and pharmaceutical research.