Mimulus
Sp. Pl. 2: 634. 1753.
Herbs, perennial, terrestrial or semi-aquatic. Stems ascending to erect, 4-angled, winged, sometimes narrowly, glabrous. Leaves basal and cauline, opposite; petiole present or absent; blade sometimes semi-fleshy, margins dentate to subentire, venation brochidodromous. Inflorescences axillary, flowers solitary at medial to distal nodes; bracts absent. Pedicels present, shorter or longer than calyces; bracteoles absent. Flowers mostly erect, not strongly reflexed and appressed in fruit; sepals 5, calyx bilaterally symmetric, tubular, tube midveins wing-angled, lobes deltate to triangular; petals deciduous, 5, corolla blue to violet, purplish, or light pink, rarely white [yellow in M. bracteosus], bilaterally symmetric, strongly bilabiate, dorsoventrally compressed, abaxial lobes 3, adaxial 2; stamens 4, adnate to middle of corolla, didynamous, filaments glabrous; ovary 2-locular, placentation axile; stigma bilamellate. Fruits capsules, apex rounded to truncate, wall smooth, eglandular, dehiscence loculicidal. Seeds 500–1000, brown, narrowly ellipsoid, flattened, wings absent. x = 8, 11.
Distribution
North America, s, se Asia (se China, India, Indochina), s Africa, Indian Ocean Islands (Madagascar), Australia, introduced in w Europe.
Discussion
Species 8 (2 in the flora).
A strictly defined Mimulus is sister to the radiation of Phrymaceae that has occurred primarily in Australia (P. M. Beardsley and R. G. Olmstead 2002; Beardsley et al. 2004; Beardsley and W. R. Barker 2005; Barker et al. 2012). In addition to those in North America, six Mimulus species are natives of the Eastern and Southern hemispheres; these include M. aquatilis A. R. Bean (northeastern Australia), M. bracteosus P. C. Tsoong (southeastern China), M. gracilis R. Brown (Australia), M. madagascariensis Bentham (Madagascar), M. orbicularis Wallich ex Bentham (mainland Southeast Asia), and M. strictus Bentham (Africa, India). Only M. gracilis and M. ringens have been subject to molecular analysis, but morphological similarities among these species indicate that they are monophyletic (Barker et al.).
The clade including strictly defined Mimulus is sister to the essentially western American monkeyflower species, which are treated here within separate genera. These can be divided into two groups: those with axile placentation and with long pedicels (Erythranthe) versus those with parietal placentation and short pedicels (Diplacus and Mimetanthe). Molecular data confirm that Erythranthe and Diplacus/Mimetanthe are in separate lineages and are not the closest relative of each other. Closest to Diplacus and Mimetanthe is the Mexican-Central American Hemichaena Bentham, also with parietal placentation. Closest to Erythranthe is the monospecific Leucocarpus D. Don of Central America to northern South America, which has axile placentation.
Mimulus alatus and M. ringens maintain strongly distinct morphologies over a broad region of sympatry, but the two have been reported to hybridize naturally along the Patapsco River in Maryland (D. R. Windler et al. 1976). In a mixed population, about 40 percent of the individuals apparently were F1 hybrids; consistently high pollen stainability of the parental plants suggests that backcrossing was not occurring. The two species differ in chromosome number (M. alatus, 2n = 22; M. ringens, 2n = 16, 24), but chromosome numbers were not determined in this study.
Selected References
Lower Taxa
Key
| 1 | Leaves sessile; blade bases auriculate-clasping or subclasping; stems not or narrowly winged; fruiting pedicels 10–17 mm or 20–45(–60) mm, longer than calyces. | Mimulus ringens |
| 1 | Leaves petiolate; blade bases rounded to cuneate; stems narrowly winged; fruiting pedicels 5–14(–30) mm, shorter than calyces. | Mimulus alatus |