Mimulus gemmiparus W.A. Weber (Scrophulariaceae), a rare endemic of Colorado, has a novel life history that depends on an unusual method of vegetative reproduction. The plants are functionally annuals; however, reproduction is asexual via propagules that have been termed gemmae. The morphological identity and the evolutionary antecedent of these propagules are unclear. We approached this problem through developmental analysis of the propagules and comparative analysis with the suspected progenitor species, Mimulus guttatus. In Mimulus gemmiparus there are two meristems initiated in the axil of each leaf primordium. The distal meristem has the potential to become either a lateral branch or a flower, and the proximal meristem becomes a vegetative propagule (the gemma) that is ultimately surrounded by an expanded, saccate petiole. The first leaves of the propagules are thickened and are the site of nutrient storage. Consequently, these propagules can be characterized morphologically as brood bulbils. M. guttatus also has two meristems in each leaf axil; however, the proximal meristem typically remains dormant and does not serve any function in the life history of this species. The propagule of M. gemmiparus corresponds both architecturally and developmentally to the proximal meristem of M. guttatus.

Key words: asexual reproduction, bulbil, development, Mimulus gemmiparus, Mimulus guttatus, propagule