Developmental analysis of the evolutionary origin of vegetative propagules in Mimulus gemmiparus (Scrophulariaceae)

Abstract

Mimulus gemmiparus (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 comparative developmental analyses of M. gemmiparus and the presumed progenitor species, Mimulus guttatus. In M. gemmiparus there are two meristems initiated in the axil of each leaf primordium. The distal meristem has the potential to produce either a lateral branch or a flower, and the proximal meristem becomes a vegetative propagule (the gemma) that is ultimately surrounded by an expanded, ensheathing 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. Mimulus guttatus also has two meristems in each leaf axil; however, the proximal meristem typically remains dormant and serves no function in the life history of this species. Based on architectural and developmental correspondence, we hypothesize that the propagule of M. gemmiparus is homologous to the proximal meristem of M. guttatus. Comparative analysis shows that evolution of the bulbil has involved both the incorporation of features present in shoots of M. guttatus and the acquisition of novel features.

Developmental Plasticity of Shoot Architecture: Morphological Expression and Ecologically Relevant Onset in Locally Adapted Populations of Mimulus guttatus

“…Plants of all populations have opposite decussate phyllotaxy with two serial axillary meristems borne in each leaf axil. The distal meristem is capable of becoming either a flower or a lateral branch; the proximate meristem typically remains quiescent (Moody et al 1999;Baker et al 2012). In general, M. guttatus in permanently wet habitats are perennial, whereas populations with temporary water availability are annual .…”

Aspects of sexual failure in the reproductive processes of a rare bulbiliferous plant, Titanotrichum oldhamii (Gesneriaceae), in subtropical Asia

“…In a study of flower and bulbil development of T. oldhamii, Wang and Cronk (2003) found that a single floral meristem converts into a cluster of ca. 60-80 bulbils, unlike other bulbiliferous plants such as Polygonum viviparum and Mimulus gemmiparus, in which a single flower is replaced by a single bulbil (Diggle 1997;Moody et al 1999). As many as 20-30 clusters are produced per side branch and 20 or more branches can be present per plant (Fig.…”

Altered expression of GFLO , the Gesneriaceae homologue of FLORICAULA/LEAFY , is associated with the transition to bulbil formation in Titanotrichum oldhamii

“…Polygonum viviparum and Mimulus gemmiparus; Diggle 1997; Moody et al 1999) perhaps based on a common genetic mechanism in these plants. Bulbil production in such plants is often related to environmental conditions, as well as intrinsic factors such as position on the inflorescence (Diggle 1997).…”