Decumbent Goldenbush [Isocoma menziesii (Hook. & Arn.) Nesom var. decumbens (Greene) Nesom]

Decumbent Goldenbush [Isocoma menziesii (Hook. & Arn.) Nesom var. decumbens (Greene) Nesom]

List: CNPS List 1B R-E-D Code 2-2-2

State/Federal. Status -- None ASTERACEAE Apr.-Nov.

Global Rank G?T? State Rank S?

Distribution: San Diego County, Orange County, San Clemente Island, Santa Catalina Island; Baja California, Mexico

Habitat: This species is presumed to utilize coastal sage scrub habitat intermixed with grassland, and is more partial to clay soils than other closely related varieties.

Known Sites: Under Nesom's concept (Phytologia, February 1991), variety decumbens is an arachnoid form of the widely ranging Isocoma menziesii with mostly gray tomentose entire leaves (which can have a few teeth near the apex). Such forms are concentrated in San Diego County in the vicinity of Bonita and in their purest forms range roughly northward to the vicinity of Miramar Naval Air Station. While these plants appear quite distinctive and may grow sympatrically with primarily glabrous or lightly haired and somewhat glutinous leaved plants (identified by Nesom as variety menziesii), elsewhere in coastal portions of this county are numerous populations with seemingly intermediate traits such as within the Camp Elliot area. Substantial numbers of plants conforming to the description of variety decumbens grow on both sides of Proctor Valley Road in eastern Chula Vista, from west of Rolling Ridge Road to Gobblers Knob.

Status: The status of Decumbent Goldenbush in San Diego County is unknown; more information is needed on the limitations under which variety decumbens is assignable to specific populations. Given the presumed definition, populations dominated by relatively short shrubs with few teeth on relatively hairy leaves can be assigned to variety decumbens. Taxonomic work is necessary to adequately assess the coastal goldenbushes; currently there still seems to be disagreement on this genus with differing concepts as to varieties or subspecies. This variety is not addressed within the Jepson Manual (1993). Provisionally, it is recommended that sizeable portions of all substantial populations fitting the description of putative variety decumbens be protected until more information is available. It should also be noted that plants similar to inland forms of typical Isocoma menziesii var. menziesii but with a decumbent to prostrate habit occur on the sea bluffs at the southern tip of Point Loma, about the salt marsh at Imperial Beach, and are reported at scattered locales north of La Jolla (usually quite near the ocean). These plants are mostly glabrous. A specimen of variety sedoides with broadly spatulate leaves, from ocean bluffs near Encinitas, was examined in the herbarium of the San Diego Natural History Museum. This variety is a form not previously recorded from San Diego County, and the influence of this predominantly northern form may account for some of the diversity of traits observed in the region. Moreover, variety vernonioides is present in northern San Diego County (it is often the dominant form in western Riverside County), as indicated by shrubs with leaves that are toothed along most of the margins. One anomalous observation is of a small population of plants along H Street in Chula Vista east of the 805 Freeway which has very narrow leaves with quite prominent teeth along the margins, somewhat reminiscent of Machaeranthera juncea.

Copyright May 1994 Craig H. Reiser.

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