Monolopia is a genus of annual flowering plants in the daisy family, Asteraceae (order Asterales). It is small — comprising around five species — and is entirely endemic to California, making it one of the state's characteristic wildflower genera.
Plants are annuals growing to about 60 cm tall, with erect, branched stems. The leaves are mostly cauline and alternate (the proximal pairs sometimes opposite), with blades narrowly oblong, oblanceolate, or lance-linear in outline; margins are sinuate-dentate or entire, and both leaf surfaces are loosely to densely woolly. Flower heads are usually radiate and typically borne singly (in M. congdonii they are arranged in corymbiform arrays). The involucre is hemispheric, 5–13 mm in diameter, with 4–11 phyllaries in a single series that are persistent and usually spreading, becoming reflexed in fruit in M. congdonii; the phyllary faces are woolly and often tipped with black hairs. Ray florets number (7–)8(–11), are pistillate and fertile, with corollas typically bright yellow (cream in M. major). Disc florets number 20–100, are bisexual and fertile with yellow corollas. The fruits (cypselae) are obcompressed or somewhat prismatic and usually lack a pappus (scales present only in M. congdonii). The base chromosome number is x = 13.
Species within the genus occupy different parts of California's Coast Ranges, Sierra Nevada foothills, and the Central Valley. Monolopia lanceolata (common monolopia) is the most widespread, ranging from Contra Costa and San Joaquin counties south to San Diego and Riverside counties. M. major (cupped monolopia) is found from Tehama County south to Ventura County, while M. gracilens (woodland monolopia) occupies a coastal range from Contra Costa to San Luis Obispo counties. M. stricta (Crum's monolopia) is restricted to an inland belt from Monterey and Merced counties south to Kern County.
Distribution
All species of Monolopia are endemic to California, USA, with ranges concentrated in the Coast Ranges, Central Valley, and Sierra Nevada foothills. The most widespread species, M. lanceolata, extends from the San Francisco Bay Area south to San Diego and Riverside counties; other species are more narrowly distributed within the state.
Ecology
Monolopia species are warm-season annuals typical of California's grasslands, foothill woodlands, and open chaparral edges. They are characteristic of the spring wildflower assemblages of the Central Valley and surrounding foothills, flowering from approximately February through May depending on elevation and latitude.
Taxonomy Notes
Monolopia belongs to the tribe Madieae within Asteraceae. The Flora of North America treatment (vol. 21, by Dale E. Johnson) recognises five species; M. congdonii (San Joaquin woollythread) was formerly placed in the segregate genus Lembertia. The base chromosome number is x = 13.
