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Literature Review

Mecca Aster

Xylorhiza cognata

USFWS: No official status
CDFG: No official status

Background

Distribution, Abundance and Trends. Mecca Aster is endemic to the Indio Hills and the Mecca Hills. It typically occurs in these fluvial mud hills in washes and along the lower slopes. It is known to occur from Macomber Palms and Biskra Palms on the Coachella Valley Preserve east along the base of the Indio Hills. The easternmost location in the Indio Hills is in the vicinity of Curtis Palms, east of the Granite Construction facility. In the Mecca Hills, it occurs in Painted Canyon, in Box Canyon along Hwy 195, and in Hidden Spring Canyon. Most of the known occurrences are along roads or well-traveled hiking routes; it is likely that the species has a scattered distribution throughout the Mecca Hills (Stewart 1991). Information on population size and density is not available. The following table summarized the number of plants observed at 17 occurrences reported by the California Natural Diversity Data Base (CDFG 1997).

LOCATION	NUMBER OF PLANTS
	PRE-1976	1976	1984	1985	1986	1995-1997
INDIO HILLS - MACOMBER PALMS			660
INDIO HILLS - BISKRA PALMS: several sites from 3.2 mi. to just SE of Biskra Palms			200/ 7/ 250	7 3.2 mi. SE
MECCA HILLS - PAINTED CANYON	Collected in '38	25 1 mi. up
MECCA HILLS - HIDDEN SPRING: from 1mi. SE to 2.8 mi. SSE of Hidden Spring	COllected in '27, '30, '32, '46				<10/ <10/ 50
MECCA HILLS - 1.4 mi. S of SHEEP HOLE OASIS					50-100
MECCA HILLS - SOUTH OF SHAVERS WELL: from	Collected in '36			520/ 2.5 mi. SW 49 1.1 mi. S	100-1000+ 4.2 mi.SW
MECCA HILLS - THERMAL MINE AREA 1 mi. S of Thermal Canyon						17/ 1341
1 Numbers of plants given are as reported to the Natural Diversity Data Base by various observers including J. Stewart, T. Bennett, A. Sanders, M.D. Clary, W. Follett, R. Ferris, and by Lilburn Corp (1995). In some areas (e.g. Hidden Spring area) more than one occurrence is reported, with numbers of plants separated by a slash.

Jon Stewart, a botanist familiar with the species, has suggested that it may be associated with two intergraded geologic formations found in these hills, the Palm Springs formation and the Canebrake formation (Stewart 1991). These formations are similar in age and are both fluvial deposits; the Palm Springs formation is composed of sandstones and clays while the Canebrake formation includes granitic conglomerates of larger materials. Stewart noted a strong correlation between the known occurrences of this species and the Palm Springs and Canebrake geologic formations. It should be noted that these two formations are not restricted to the Coachella Valley.

It may be that the observation of this species in proximity to major roads has given the false impression that the plants are very common. While the species may be numerous in places, its limited geographic distribution and restricted soil preferences suggest that it is only very locally common.

Threats and Limiting Factors. Threats to this species include cumulative habitat loss and degradation of the existing habitat from off road vehicle activity, illegal dumping, sand and gravel mining (J. Dice pers. comm.) and edge effects. Off-road vehicle activity that formerly threatened populations in the Mecca Hills has been eliminated with the designation of this area as wilderness. Off-road vehicle activity in the Indio Hills may threaten several populations and may increase as other areas become unavailable through development or protection. For example plants in the vicinity of Macomber Palms occur in a wash where they are vulnerable to off-road vehicles. Isolation of the two significant populations in the Indio Hills and Mecca Hills may reduce genetic diversity.

Special Considerations. This species is thought to be associated with soils of the Palm Springs and Canebrake formations, which are limited in distribution within the Plan area. However, current maps of these formations do not exactly correspond with the distribution of this plant (see model parameter summaries.