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Quillaja comprises three to four species in southern Brazil, Peru, Argentina and Chile, of which only Q. saponaria is in cultivation. They are evergreen trees or shrubs, with caducous stipules. The leaves are simple, alternate and spirally arranged; leathery, and with shallowly toothed margins. Inflorescences are terminal and axillary, paniculate and few-flowered. The flowers may be hermaphrodite or unisexual; they are 5-merous, with a fleshy, five-lobed nectary disc in the centre. The fruit is a leathery, dehiscent follicle; each flower produces five follicles, which are partially fused at the base. The numerous seeds are winged (Zardini 1973, Pennington et al. 2004).