Description
Diplacus clivicola is a small, generally single-stemmed annual with opposite, mostly elliptic leaves and large, pink, showy flowers. The entire plant is covered with glandular hairs that emit a musky odor when rubbed between the fingers (Lorain and Moseley 1989).
Recent work with the taxon (Lorain and Moseley 1989, Lorain and Moseley 1990, Lorain 1991,1992) has identified additional characteristics that are especially helpful for identification during field investigations. These investigators described Diplacus clivicola as having "distinctly pink" flowers and a musky, sweet smell when the herbage is rubbed.
Diagnostic Characteristics
The following characteristics help distinguish Diplacus clivicola from other small, annual, pink/purple-flowering Mimulus species occurring within its range, specifically M. breweri and M. nanus. Mimulus breweri has rather inconspicuous, small (<10 mm), slender flowers, whereas, M. clivicola has larger (up to 2.5 cm), funnelform flowers. Mimulus nanus has deep magenta flowers on pedicels 1-3 mm in length, has only a few hairs, and occurs in dry, open, often sandy or gravelly places, whereas, M. clivicola has distinctly pink flowers on pedicels 3-7 mm in length, is covered with rather dense sticky hairs, and occurs usually in more mesic sites. Neither M. breweri nor M. nanus has the distinct musky, sweet odor characteristic of M. clivicola (Lorain and Moseley 1989, Lorain and Moseley 1990).
Habitat
Diplacus clivicola occurs on bluffs and in vegetation openings, on disturbed slopes, and in well-developed loam soils from 500-2000 m in elevation (FNA 2019). This species is restricted to a very specific set of habitat parameters. Plants typically occur in open pockets of moist, exposed mineral soil created by natural disturbances (such as erosion, big-game activity, etc.) or human-caused disturbances (roadcuts, etc.). They are almost exclusively found on southern exposures (southeast, south, southwest) with steep slopes (generally > 60%) in microhabitats that hold moisture during the spring.
Differences in elevation, soils, and plant associations exist among the northern Idaho, north-central Idaho, and northeastern Oregon sites. Elevations range from 1600 to 4100 ft (mostly < 3600 ft) in northern Idaho, from 4200 to 5600 ft in west-central Idaho (with a single site extending to 7100 ft), and from 2500 to 5500 ft (mostly > 3500 ft) in northeastern Oregon. Soils range from deep, loose, decomposed granitics in northern Idaho, to deep to thin basaltics in west-central Idaho, to shallow, gravelly basaltics in northeastern Oregon (Lorain and Moseley 1990, Lorain 1991,1992).
Most Diplacus clivicola populations in northern Idaho occur in Douglas-fir/Idaho fescue (Pseudotsuga menziesii/Festuca idahoensis), Douglas-fir/ninebark (Pseudotsuga menziesii/Physocarpus malvaceus), and grand fir/ninebark (Abies grandis/Physocarpus malvaceus) habitat types (Cooper et al. 1987). The plant associates in these habitat types include Collomia linearis, Clarkia pulchella, Sedum lanceolatum, Pteridium aquilinum, Collinsia parviflora, Achillea millefolium, Agropyron spicatum, and Triodanis perfoliata. Clarkia pulchella and Collomia linearis are excellent indicators for identifying potential habitat (Lorain and Moseley 1989, Lorain and Moseley 1990, Lorain 1991,1992).
Most of the populations in west-central Idaho occur in a much drier sagebrush habitat type, the stiff sagebrush/Sandberg's bluegrass (Artemisia rigida/Poa secunda) habitat type (Tisdale 1986) with the following plant associates: Castilleja oresbia, Allium tolmiei var. persimile, Allium acuminatum, Lomatium dissectum, and Clarkia pulchella. Other populations were found in habitats similar to northern Idaho, Douglas-fir/mountain snowberry and Douglas-fir/ninebark habitat types with the following plant associates: Carex geyeri, Collinsia parviflora, Antennaria luzuloides, Collomia linearis, Potentilla glandulosa, Paeonia brownii, Amelanchier alnifolia, Spiraea betulifolia, and Penstemon payettensis (Lorain and Moseley 1990, Lorain 1991,1992).
Most populations in northeastern Oregon occur as part of the Cusick's camas seepage plant community type (Camassia cusickii) (Johnson and Simon 1987), which tends to occur beneath basalt rims where seepage water persists into early summer. Plant associates in this community type include Camassia cusickii, Allium acuminatum, Calochortus eurycarpus, Sedum stenopetalum, Collomia linearis, Bromus tectorum, Collinsia parviflora, Achillea millefolium, Agropyron spicatum, Eriogonum heracleoides, and Perideridia bolanderi. Annual Mimulus species such as M. nanus, M. breweri, M. floribundus and M. guttatus, were often found in this community type. Camassia cusickii was the best indicator for identifying potential habitat in northeastern Oregon (Lorain and Moseley 1990, Lorain 1991,1992).
Reproduction
Spring precipitation, availability of suitable microhabitat, and certain activities of big game animals seem to have high correlation with the germination and establishment of this species. Availability of spring moisture appears to be a necessary requirement. All known populations occur in moist microhabitats, such as seepages caused by perched water tables, areas where water channels following rain, or in big-game tracks that hold water. Although these sites may dry out later in the summer, they provide a moist substrate in the spring for seed germination and flowering (Lorain and Moseley 1989, Lorain and Moseley 1990, Lorain 1991,1992). Suitable microhabitat, patches of exposed mineral soil, which can result from natural causes such as erosion and the movements of big game or man-caused disturbances such as road-building, appears to be another necessary requirement. The movement of deer and elk not only create areas of exposed mineral soil and tracks that trap water, ideal conditions for germination and growth of the species, but also serve to disperse the seeds. Another aspect of big game activity which may be favoring the establishment of this species, is their grazing of cheatgrass (Bromus tectorum), a very competitive introduced winter annual. This may reduce competition for limited soil moisture on southern slopes, especially during droughty springs, and favor the establishment and growth of Diplacus clivicola (Lorain 1989).
Research on seed germination and early growth characteristics was conducted by researchers in the Department of Biological Sciences at the University of Montana (Pavek and Mitchell-Olds 1990). Seed germination required three weeks of stratification (moist, cool conditions of 100% humidity at approximately 40 degrees C). There was a high percentage of germination (no actual values given) occurring 12-19 days after the stratification period was complete. First flower buds developed at approximately 5 weeks, just after the second pair of leaves when the plants were only 0.5 inches tall.