San Diego County Needlegrass [Achnatherum diegoensis (Swallen) Barkworth]

San Diego County Needlegrass [Achnatherum diegoensis (Swallen) Barkworth]

Listing CNPS List 4 R-E-D Code 1-2-1

State/Federal. Status -- None POACEAE May-Jun.

Global Rank G3 State Rank S3.2

Distribution: San Diego County, Santa Cruz Island, Anacapa Island, Santa Rosa Island, San Miguel Island, San Nicolas Island; Baja California, Mexico

Habitat: Chaparral and Sage Scrub ecotone is utilized by this robust perennial bunchgrass. The soil on McGinty Mountain is mapped as Las Posas stony fine sandy loam; populations elsewhere sometimes occur on San Miguel Exchequer rocky silt loams.

Known Sites: This is a quixotic bunchgrass found in coastal sage scrub in southwestern San Diego County. A healthy population grows on the lower slopes of McGinty Peak. It is also seen south of Lower Otay Lake, and on hillsides west of Spring Canyon on Otay Mesa. It grows in metavolcanic soils west of Rolling Ridge Road and south of a sharp bend in Proctor Valley Road near Chula Vista. Old reports are from Proctor Valley and Lee Valley. Recent reports of substantial populations come from the Jamul Mountains; as well as substantial populations on the Channel Islands which have heretofore gone unnoticed.

Eleven specimens for Baja are found in the San Diego Natural History Museum's herbarium. It is recorded as far south as 30 27' North where it was collected by Moran (SD 100745) on a rocky slope at Agua de Tanilo. It was seen growing on a hill overlooking Rodriguez Dam east of Tijuana, Mexico, intermixed with both Nassella lepida and Nassella pulchra. At this locale all three species were in seed and quite distinct, with the leaf blades of N. lepida noticeably narrower than the other two species. Also, the strongly bent awn of A. diegoensis contrasted with the shorter awn of N. lepida and the long, straight awn of N. pulchra.

Status: San Diego County Needlegrass is slowly declining on the periphery of urban expansion, and is likely to sustain more impacts in the 1990's as the southern foothills receive development pressures. When not in seed, it is only with extreme difficulty that this grass is identified in the field. Coastal hillsides in Chula Vista, Otay Valley, Jamul, and San Ysidro should be carefully scrutinized for this species. Fall and winter surveys in these areas may miss this cryptic species which can mimic the common Nassella pulchra and Nassella lepida. More field collection data is needed for San Diego County, to more accurately determine its local rarity. Provisionally, all sizeable populations should be protected, and substantial portions of smaller populations are recommended for biological open space.


Copyright May 1994 Craig H. Reiser.

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