The morphological variation of the west-mediterranean Odontites viscosus (L.) Clairv.(Scro- phulariaceae-Rhinanthoideae) was studied mainly by means of biométrie analyses of 24 populations covering the whole range of the species-area, and by the revision of all herbarium material available. From the 47 characters studied, the following were found to show a clear geographical pattern of variation: length, shape and pubescence of bracts; shape of lateral lobes of the lower lip of the corolla; length of glandular hairs and shape of the gland-head; shape of capsule. Various combinations of these characters allow the taxonomic subdivision of the species into five subspecies representing geographical races. Geographically and morphologically, the Spanish subsp. australis takes a central position, overlapping in the variation of the characters mentioned above with the taxa occupying neighbouring areas: subsp. lusitanicus (small area in southern Portugal), subsp. eriopodus (Middle Atlas of Morocco,W-Algeria), and the heterogeneous type-subsp. viscosus (Pyrenees, Southern France, Western Alps northwards to the Valais : many local races exist which differ only slightly in the shape and the pubescence of the bracts). O. granatensis Boiss., a probably extinct brown-violet flowering endemic of the Sierra Nevada, was recognized to belong also to the viscosus-group and therefore was given subspecific rank too. Ecologically the subspecies behave similarly, being mainly restricted to the mediterranean climate with dry and warm summers and moist winters. The altitudinal amplitude of O. viscosus s.l. ranges from 50m (subsp. lusitanicus) to 2100m (subsp. granatensis), but the main distribution of the much more widespread taxa subsp. viscosus and subsp. australis is confined to the hill and the montane belt between 400 and 1500m. All subspecies occur in dry light forests, open woodlands, or different types of garigues. O. viscosus is a characteristic species of the light holly oak forest (Quercetum ilicis) as well as of the garigue-vegetation replacing the forest (Rosmarinetalia). In the mountains there is a preference for light and dry pine forests, e.g. in the Western Alps, where O. viscosus climbs up to 1800m as a characteristic species of the xerothermous Ononido-Pinion-alliance.