Little Mousetail [Myosurus minimus L. ssp. apus Greene]

Little Mousetail [Myosurus minimus L. ssp. apus Greene]

Listing CNPS List 3 R-E-D Code 2-3-2

State/Federal. Status -- /C2 RANUNCULACEAE Mar.-Jun.

Global Rank G5T2Q State Rank S2.2

Distribution: Riverside County, San Bernardino County, San Diego County, Butte County, Alameda County, Contra Costa County, Colusa County, Solano County, Stanislaus County, Kern County; Oregon; Baja California, Mexico

Habitat: Vernal Pools are the habitat utilized by Little Mousetail. Typically this cryptic species grows in the deeper portions of vernal pool basins sprouting immediately after the surface water has evaporated. The stature of plants and population densities of Myosurus minimus change dramatically from wet to dry years. Soils are mapped as Huerhuero loam for both Little Mousetail sites near Dillon Road in the southwestern portion of the county, and for Stewart Mesa in the northwestern portion of the county. Bosanko clays are reported for a site in the Gavilan Hills of Riverside County.

Known Sites: Vernal pools north of Peñasquitos Canyon, purchased as mitigation by CalTrans, possess a limited population of Little Mousetail. A substantial population of this plant grows on the periphery of the vernal pools and even into the adjacent mesic grasslands at the south end of Dillon Road on Otay Mesa. During dry years Myosurus has not been found at this Dillon Road locale, while following one particularly rainy winter, the colony consisted of several hundred mature individuals. Several healthy populations of variety apus occur in vernal pools south and north of Mass 3 Road on Camp Pendleton. Recent reports are from vernal pools on the mesa north of the eastern arm of Lower Otay Lake in the K6 pools; as well as within vernal pools near the intersection of Calbaugh and Brea in Ramona. An older report is from the west side of Proctor Valley Road 1.9 miles north northeast of Upper Otay Reservoir. Data Base reports are from the south end of Santo Road in Tierra Santa, west of Ramona 1.4 miles north of junction of Highway 67 and Highland Valley Road, west of Ramona just south of the Ramona Airport, approximately 0.5 mile south of Lower Otay Campground, above Dennery Canyon along Highway 117 on Otay Mesa, and 0.75 mile east of Highway 75 and 0.25 mile south of Highway 117 on Otay Mesa. A sizeable population occurs in Hemet in western Riverside County near the intersection of Florida and Warren. An estimated 1000 plus plants were observed in a massive vernal pool on the corner of Stowe Road and California Road near Hemet during spring 1992. An old report by Munz places this species in a vernal pool near March Air Force Base in western Riverside County. Data Base reports from Riverside County are for Hartford Springs County Park, from four pools on Mesa de Burro, as well as two pools from Mesa de Colorado on the Santa Rosa Plateau.

Four Baja California specimens are found at the herbarium for the San Diego Natural History Museum; south to 31 16' North where collected by Moran (SD 101579) at a vernal pond on the south side of a river near Erendira. Limited numbers were seen in a vernal pool complex north of Cerro Bola and west of the Tecate/Ensenada Highway in Valle de las Palmas, Baja California.

Status: Little Mousetail is declining throughout its limited Southern California range. The Camp Pendleton populations are threatened by development for varied military activities; locales near Hemet are clearly endangered by urban expansion. In the Dieter Wilken treatment of Myosurus in the Jepson Manual (1993), subspecies apus is not given distinctive recognition, but is mentioned within the discussion of M. minimus. The relationship of disjunct Southern California populations with plants in the San Joaquin Valley needs to be addressed. Until taxonomic questions are resolved, it is recommended that all Southern California populations should be protected.

Copyright © May 1994 Craig H. Reiser.

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