Lyon's Pentachaeta

Pentachaeta lyonii

Description

Pentachaeta lyonii (Lyon's pentachaeta), is a 2.4-18.9 in (6-48 cm) tall annual in the aster family (Asteraceae or Compositae) with yellow flowers that bloom from April to June. It is distinguished from other members of the genus by its hairy phyllaries, larger numbers of pappus bristles, and its reddish branches originating from the upper portion of the plant. The corollas of the ray flowers are typically curled and the leaves are narrowly linear with ciliate margins. There are no other members of the genus in the region.

Asa Gray named Pentachaeta lyonii (Lyon's pentachaeta) in 1886 from a plant collected by William Lyon near Palos Verdes Mountain in Los Angeles County. David Keck renamed the plant Chaetopappa lyonii in 1958, and the name was recognized the following year. Pentachaeta is recognized as the accepted genus through a 1973 monograph on the taxonomic status of Pentachaeta and Chaetopappa, in which comparisons of morphology, anatomy, and breeding systems demonstrated that the two genera are not closely related.

Habitat

Lyon's pentachaeta is found on clay soils in ecotonal areas between grasslands and shrublands. It occupies pocket grassland sites that intergrade with shrublands, as well as the edges of roads and trails. This habitat is largely dominated by introduced old world grass and herb genera such as Avena, Brassica, Bromus, Centaurea, and Erodium. Species typically associated with Lyon's pentachaeta include turkish rugging (Chorizanthe staticoides ), Catalina mariposa lily (Calochortus catalinae ), purple needle-grass (Nassella pulchra ), and annual members of the phlox family (Polemoniaceae ). The habitat of Lyon's pentachaeta is characterized by a low percentage of total plant cover and exposed soils with a microbiotic crust, partially assisting in reducing competition with other species. The rodents Perognathus ssp. and Peromyscus ssp. and harvester ant colonies (Pogonomyrex ssp.) also control the density of associated vegetation.

Distribution

Lyon's pentachaeta is a narrowly localized endemic with a highly fragmented and discontinuous distribution in the Santa Monica Mountains and the western Simi Hills. There are very few collections of Lyon's pentachaeta; the majority were made around the turn of the twentieth century from locations where the species has been extirpated, including Palos Verdes Peninsula and Santa Catalina Island. The first record from the Santa Monica Mountains was made in 1926 from an unknown location in the Malibu Hills. Lyon's pentachaeta was not documented again from this mountain range until 1964, when Peter Raven was collecting Santa Monica Mountain flora. That population has since been extirpated by conversion to agriculture. David Verity discovered the easternmost population of Lyon's pentachaeta in the Santa Monica Mountains at Stunt Ranch in 1977.

Lyon's pentachaeta is currently known from five population units in the Santa Monica Mountains and the western Simi Hills, a distance of approximately 20 mi (32 km), distributed in a highly fragmented landscape. The East unit is one occurrence with 4,000 individuals; the Mulholland crest unit has three occurrences with 1,200 individuals; the Central unit has seven occurrences with 28,000 individuals; the Conejo Ridge unit has seven occurrences with 2,900 individuals; and the North unit has four occurrences with 1,000 individuals. Five of these occurrences are known to exist on public lands managed by the National Parks Service (NPS), the Las Virgenes Municipal Water District, and Conejo Open Space and Conservation Agency (COSCA). The three occurrences on public lands—Stunt Ranch, Malibu Creek State Park, and Arroyo Sequit—appear to have become extirpated since 1993. The remaining locations are on privately owned land, where they face considerable threats. The aggregate number of Pentachaeta lyonnii individuals is less than 50,000, most of which are in occurrences that have less than 1,000 individuals.

Threats

Almost all the occurrences of Lyon's pentachaeta on public land are threatened by active primary and secondary threats from existing or proposed development. Primary threats include those that eliminate populations during construction. Secondary threats include the influence of the project on the surrounding environment in the form of local disturbance facilitating the introduction of competitive weeds and alteration of ecosystem processes. Other sites containing potential habitat for Lyon's pentachaeta are limited, reducing the likelihood of finding additional safe and viable populations of this species.

Lyon's pentachaeta continues to be harmed by urban development. The Lake Eleanor Hills Project approved by the City of Westlake Village eliminates a habitat containing several thousand plants. The approved and developed Lake Sherwood Golf Course and Ronald Reagan Presidential Library eliminated significant habitat for this plant. Sites that have been set aside as ex situ mitigation areas with seed and soil transported from Lyon's pentachaeta populations destroyed in grading operations for development have failed to successfully establish viable populations. The establishment of an in situ management area was required as mitigation for the removal of habitat at Lake Sherwood Golf Course that supported over 3,000 Lyon's pentachaeta individuals. The site was adversely affected by changed hydrology, competition with non-native species, loss of habitat for potential pollinators, and elimination of natural fire cycles. There was no buffer zone, and the mitigation site failed to maintain a self-perpetuating population of Lyon's pentachaeta.

Only a 50 ft (15 m) buffer for avoidance of rare plant populations currently is required by local permitting agencies in Ventura County and the city of Thousand Oaks. A 50 ft (15 m) buffer zone falls within the 100-200 ft (30-60 m) fuels modification zone required in California and is usually maintained by disking and mowing. This practice modifies or destroys the habitat characteristics essential to sustaining viable populations of Lyon's pentachaeta. Two projects, one with a reported 10,000 Lyon's pentachaeta individuals, have been designed with its habitat designated as part of the fuels modification zone. Prior attempts to avoid or compensate for impacts have not produced conditions favorable for the long-term maintenance of Lyon's pentachaeta populations. As part of a program to mitigate the loss of a substantial population of Lyon's pentachaeta, plants grown from seed at Rancho Santa Ana Botanic Gardens were severely damaged by a white fly infestation.

Fire suppression activities resulted in the extirpation of Lyon's pentachaeta habitat during the Greenmeadow fire of 1993. The use of prescribed fire as a habitat management tool for Lyon's pentachaeta will be difficult because approved development is situated extremely close to "protected" populations.

At least two populations of this taxon have been eliminated from the secondary effects of gopher-tilling of the soil, which facilitates the growth of competitive non-native weeds. Stable populations of Lyon's pentachaeta occur in sites that have a crusty soil surface that results in lower spatial competition from non-native annual grasses. When the crust is broken, the aggressive non-native annual weeds have an "open door" to displace Lyon's pentachaeta. Populations of this plant have apparently been lost and replaced by a dense community of weeds near Stunt Ranch and along upper Westlake Boulevard.

Human-caused disturbances, such as roads, trails, and minor landform alterations, have functioned to provide a zone where the competition from aggressive, non-native annual weeds is reduced, thereby allowing Lyon's pentachaeta to grow. This artificial habitat contains a zone of highly compacted soils devoid of vegetation that graduates to a zone of high vegetative cover. Between the zones is a narrow strip of habitat of reduced competition where Lyon's pentachaeta occasionally occurs. It is not disturbance that is required for viable Lyon's pentachaeta habitat, rather it is the reduced competition from non-native species such as wild oats, brome grass, and tocalote.

Changes in the intensity of disturbance have eradicated colonies of Lyon's pentachaeta on NPS land. A linear habitat alongside a trail supported a small population for several years; however, a significant increase in equestrian use changed the character of the minor disturbance that foot traffic generated. The soils changed in texture from compacted to powder and the width of the tread increased, eliminating the narrow band of habitat occupied by Lyon's pentachaeta. Another colony on the same parkland was significantly reduced by recreational trampling. The colony occurred alongside an artificial pond that was used by swimmers and picnickers who spread blankets and towels over the site. That colony was fenced in 1988 to prevent further impacts but did not show signs of recovery.

Conservation and Recovery

The Lyon's pentachaeta survives only in 22 fragmented habitats (comprising five populations) in the Santa Monica Mountains and western Simi Hills, over a distance of about 20 mi (32 km). Only five of the habitats are on public lands, managed by the NPS, the Las Virgenes Municipal Water District, and the COSCA. These public habitats should be strictly protected against threatening activities. This is best accomplished by modifying the management plans for the areas, to ensure protection of the endangered plant. Other critical habitats of the Lyon's pentachaeta are on private land. The largest of these habitats should also 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 Lyon's pentachaeta should be monitored, and research undertaken into its biology and habitat needs, including methods of beneficial management.

Contacts

U. S. Fish and Wildlife Service
Ventura Fish and Wildlife Office
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 Complex
911 N. E. 11th Ave.
Portland, Oregon 97232-4181
Telephone: (503) 231-6121
http://pacific.fws.gov/

Reference

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.