Dudleya cymosa ssp. marcescens
|Listed||January 29, 1997|
|Description||Perennial, herbaceous, rosette-forming plant with corollas that are bright yellow to yellow with red markings.|
|Habitat||Volcanic or sandstone outcrops on lower slopes of moist canyons.|
|Threats||Habitat destruction by development, and damage caused by recreational activities.|
Dudleya cymosa ssp. marcescens, (marcescent dudleya), was first observed by Charlotte Hoak in 1932 in Little Sycamore Canyon in the Santa Monica Mountains. It was not until 1951 that this plant was described from a specimen collected three years earlier from the same location.
Dudleya cymosa ssp. marcescens is distinguished from other subspecies of Dudleya cymosa by the habit of the rosette leaves withering in the summer. The rosette leaves are 0.6-1.6 in (1.5-4 cm) long and 2.0-4.7 in (5-12 cm) wide, the caudex is 0.8-2.8 in (2-7 cm) thick, floral stems are 1.6-4 in (4-10 cm) tall, and corollas are bright yellow to yellow with red markings to bright red.
Charles Antoine Lemaire first described Dudleya cymosa in 1858 as Echeveria cymosa from a collection sent to him by the Belgian horticulturalist Louis de Smet; however, the type locality is unknown and the type specimen has been lost. Britton and Rose renamed the taxon Dudleya cymosa in 1903. Dudleya cymosa includes seven subspecies that range throughout California in the Sierra Nevada, Coast Ranges, Transverse Ranges, and the northern portion of the Peninsular Ranges. The two listed sub-species are noted, however, for having restricted distributions.
All of the dudleyas occur on volcanic or sandstone rock outcrops with specific microhabitat characteristics. Marcescent dudleya occupies the lower reaches of volcanic cliffs, canyon walls, and other sheer rock surfaes in canyons that have perennial moisture. In most locations, the topo-graphic relief has precluded soil formation; therefore, this taxon may be the only vascular plant in a microhabitat otherwise dominated by mosses and lichens.
Marcescent dudleya is known from seven occurrences in the Santa Monica Mountains, from Hidden Valley to Malibu Creek State Park, a distance of 15 mi (24 km). The number of individuals at each occurrence are estimated to be between 50-200 plants, with the total number of individuals being somewhat less than 1,000. The microhabitat requirements of the plant limit the possibility that any additional large populations will be found. The Department of Public Recreation (DPR) owns and manages lands on which half of these populations occur, while the National Park Service (NPS) manages two locations, both of which have suffered habitat degradation. One is on an administrative easement where the landowner has drastically altered the native vegetation, pine plantings in a cleared oak grove, and another in an area that receives unsupervised boulder hopping and rock climbing.
The distinct variation in marcescent dudleya between sites has given rise to speculation that this subspecies actually occurs in more areas than previously believed because of misidentifiction with similar plants at other locations. It has been suggested that a small population at Rattlesnake Canyon in Santa Barbara County shares characteristics with marcescent dudleya, and Fish and Wildlife Service (FWS) botanist Jim Bartel in 1992 made a tentative determination of marcescent dudleya for a population in the Santa Ana Mountains, Orange County. Other botanists who have also studied the systematics of these taxa question these determinations. If these additional populations prove to be marcescent dudleya, they are unlikely to alter the status of this subspecies; it will still have too few numbers in the Santa Monica Mountains confronted by too many threats.
The populations of marcescent dudleya on privately owned lands are threatened by development-induced habitat alteration and destruction. The plant is threatened by recreational rock climbing, foot traffic, collection, and fire.
Marcescent dudleya is damaged by recreational activities, primarily rock climbing. Plants are uprooted by rappeling and boulder climbing, as is the moss substrate so important to this habitat. Hikers can both degrade habitat by heavy walking and collect individual plants as they go. In addition, fire has been observed to severely reduce population densities and destroy the moss substrate that this species requires.
Conservation and Recovery
The marcescent dudleya is known from seven sites in the Santa Monica Mountains. Three of the sites are owned by the California DPR, and two by the NPS. However, these publicly owned sites are being affected by threatening land-use practices, especially intensive outdoor recreation in the habitat of the rare plant. Conservation of the marcescent dudleya requires that its publicly owned critical habitats be protected more stringently from threatening activities. The several populations on private land are threatened by development and other activities. These critical habitats should be protected. This could be done by acquiring the private land and establishing ecological reserves, or by negotiating conservation easements with the landowners. The populations of the marcescent dudleya should be monitored, and research undertaken into its biology and habitat needs.
U. S. Fish and Wildlife Service
Ventura Fish and Wildlife
2493 Portola Road, Suite B
Ventura, California 93003
Telephone: (805) 644-1766
Fax: (805) 644-3458
U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
Eastside Federal Building
911 N. E. 11th Ave.
Portland, Oregon 97232-4181
Telephone: (503) 231-6121
U.S. Fish and Wildlife Service. 29 January 1997. "Endangered and Threatened Wildlife and Plants; Determination of Endangered Status for Two Plants and Threatened Status for Four Plants From Southern California." Federal Register 62 (19): 4172-4183
"Marcescent Dudleya." Beacham's Guide to the Endangered Species of North America. . Encyclopedia.com. (March 26, 2019). https://www.encyclopedia.com/environment/science-magazines/marcescent-dudleya
"Marcescent Dudleya." Beacham's Guide to the Endangered Species of North America. . Retrieved March 26, 2019 from Encyclopedia.com: https://www.encyclopedia.com/environment/science-magazines/marcescent-dudleya
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