Narrow-leaved Nightshade [Solanum tenuilobatum Parish]

Narrow-leaved Nightshade [Solanum tenuilobatum Parish]

Listing Unlisted R-E-D Code None

State/Federal. Status -- /C2 SOLANACEAE Mar.-Apr.

Global Rank G2G3 State Rank S1.2

Distribution: San Diego County; Baja California, Mexico

Habitat: Open Chamise Chaparral or Diegan Sage Scrub are the typical habitat of the Narrow-leaved Nightshade. Oftentimes it occurs near broken surface rock on ridgelines; however, it also occurs well intermixed with sage scrub elements at xeric locales. Olivenhain cobbly loam is the soil type utilized at Lower Otay Lake and near Dillon Road.

Known Sites: Otay Mountain is a focus for populations of this species with scattered colonies found at low, medium, and higher elevations. Several dozen shrubs were noted at the periphery of grasslands on a large private inholding for Otay Mountain above the Minnewawa Campground; sizeable populations are uncommon due to the restricted rocky microhabitats preferred at these locales. Several hundred plants were found growing on the peak south of Donohoe Mountain constituting a major population. A few dozen were seen on a rocky ridge west of Donohoe Mountain. Small colonies grow adjacent to Montana Serena Truck Trail in Crest, west of Dillon Road on Otay Mesa, west of San Vicente Dam, by the Montiel Truck Trail near Lawson Valley, in the Silverwood Wildlife Sanctuary, in the hills east of Isham Springs and Jamacha Road, and at the east end of Lower Otay Lake. Small populations occur on a rocky knoll on a south-facing slope of Dictionary Hill, at San Vicente Dam on the hills overlooking the dock, and on Deerhorn Valley Road in the chaparral. There are also old reports to the east from Potrero Grade on the flanks of Tecate Mountain, Barrett Dam, Lyons Valley, and Campo. Recent reports indicate extensive populations occur in the Jamul Mountains; a small population is reported from Vista Sage Road in Jamul. Old biological survey reports note sites in Galloway Valley 1 mile southeast of the McClain Ranch, near Hidden Glen, on Mother Grundy Truck Trail, Mountain View Road northwest of Harbison Canyon, the Montiel Truck Trail south of Loveland Reservoir, Bullard Lane in Alpine, and at Hidden Glen. Data Base reports are for Woodwardia Canyon on Otay Mountain, 5 miles west of Campo, the north slope of Tecate Mountain, east of Proctor Valley Road in a side canyon at the north end of the valley, 4 miles west of the junction of the Otay Mountain Truck Trail and the Marron Truck Trail on Otay Mountain; a Data Base report from 4.5 miles south of Oak Grove along Highway 79 is well northeast of the known range and needs to be confirmed.

Only two Baja specimens are found at the San Diego Herbarium; collected by Moran (SD 111178) 1 km southwest of Rancho de la Cruz at 31 8' North. This apparent rarity in Baja California underscores the significance of San Diego County populations.

Status: Narrow-leaved Nightshade is slowly declining in San Diego County; primarily due to a variety of residential and industrial developments. The base of the Solanum tenuilobatum leaves are only sometimes lobed--more frequently they are somewhat linear, darkly colored, and quite distinct from the other, broader-leaved Solanum species found in this county. Some populations have been misidentified because obviously lobed leaves were not found on plants. The small populations which are typical for this species are being regularly accorded less significance than they merit, particularly given the species' present collection status in Baja California. Michael Nee's treatment of Solanum in the Jepson Manual (1993) treats S. tenuilobatum as a synonym of Solanum xanti, but notes this species is part of a variable complex. Given the edaphic preference of Solanum tenuilobatum to metavolcanic derived soils, its geographic isolation from more typical hairier forms of S. xanti, and its distinctive leaf shape, a more detailed taxonomic analysis is needed. Provisionally, all substantial populations are recommended for protection; sizeable portions of smaller populations are recommended to be placed into biological open space.


Copyright May 1994 Craig H. Reiser.

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