|(Gray ex Benth.) Reveal & Hardham|
The following Participating Institutions are custodians for this species in the CPC National Collection:
Rancho Santa Ana Botanic Garden
The conservation of Dodecahema leptoceras is fully sponsored.
Valerie Soza contributed to this Plant Profile.
Slender-horned spineflower is a federally-endangered, small, spreading annual in the buckwheat family (Polygonaceae), with stems reaching 3-15 cm across. The size of spineflowers varies, however, depending on annual available moisture (Ferguson et al. 1996). This annual has a basal rosette of leaves, from which rise dense flowering stalks. Slender-horned spineflower is distinguished from other spineflowers by the presence of 6 terminal awns and 6 hooked basal awns on each involucre. The involucre in this species is a group of bracts that have been fused together to enclose approximately 3 white to pink flowers within each involucre, blooming April through June (Hickman 1993; Munz 1974).
Distribution & Occurrence
Slender-horned spineflower is known from alluvial fans, floodplains, stream terraces, washes and associated benches, from 700-2500 feet (210-760 m) in elevation. It grows in riverbed alluvium high in silt and low in nutrients and organic matter; in silt-filled, shallow depressions on relatively flat surfaces surrounded by scattered, river-rounded, cobble-sized rocks (Allen 1996; Wood and Wells 1996). These sediments are on stable surfaces, usually older than 100 years (Wood and Wells 1996). The slender-horned spineflower is generally found in open areas among alluvial fan scrub, often associated with other spineflower species, and in low density of exotic grasses and other introduced weedy species.
|There have been 37 reported occurrences of slender-horned spineflower in southern California, 23 are existing occurrences and 14 have been or are presumed extirpated. These occurrences are located in 8 general areas: Bee Canyon, Big Tujunga Wash, Lytle Creek/Cajon Canyon, Santa Ana River wash, Bautista Creek, San Jacinto River, Temescal Canyon, and Vail Lake/Dripping Springs area (CNDDB 2000).|
Conservation, Ecology & Research
With respect to the reproductive biology of slender-horned spineflower, it has been demonstrated that this species has a higher level of genetic diversity, mostly within populations, than is typical for annual or endemic plant species. In addition, this large amount of genetic variation is typical of species with a predominantly outcrossed mating system. During studies, mostly ants and flying insects were observed visiting flowers of slender-horned spineflower (Ferguson et al. 1996)
Current threats include development, sand and gravel mining, flood control, hydrological alteration, proposed reservoir construction, off-road vehicle
An assessment of seed bank buffering of genetic change in slender-horned spineflower at 4 locations was conducted by Ferguson and Ellstrand, University of California Riverside (1999).
Mycorrhizal associations within slender-horned spineflower habitat were studied in 8 locations. Typically, annuals within the buckwheat family do not form mycorrhizae. However, slender-horned spineflower was found to form associations, although not likely mutualistic, with arbuscular-mycorrhizal fungi. These associations were determined not to be a limiting factor in suitable but unoccupied habitat (Young et al. 2000)
Various analyses have been conducted to characterize the habitat of slender-horned spineflower, from an ecological and geomorphic analysis. An attempt was made to characterize soils, vegetation cover, associated species, and ages of alluvial sediments that support populations of slender-horned spineflower (Allen 1996;
Wood and Wells 1996).
In addition, an investigation was made into the population biology of the slender-horned spineflower at 4 sites to determine population demographics, breeding systems, and genetic variation (Ferguson et al. 1996).
USFWS. 1986. Proposed Endangered Status for Eriastrum densifolium ssp. sanctorum (Santa Ana River Woolly-star) & Centrostegia leptoceras (Slender-Horned Spineflower). Federal Register. 51, 68: 12160-12184.
USFWS. 1987. Determination of Endangered Status for Eriastrum densifolium ssp. sanctorum (Santa Ana River Woolly-star) & Centrostegia leptoceras (Slender-Horned Spineflower). Federal Register. 52: 3626-36270.