Hoffmann's Slender-flowered Gilia
Hoffmann's Slender-flowered Gilia
Gilia tenuiflora ssp. hoffmannii
|Listed||July 31, 1997|
|Description||Small, erect annual herb; flowers are purplish and funnel-shaped below, widening to five pinkish corolla lobes.|
|Habitat||East Point locality of Santa Rosa island as a component of dune scrub vegetation with sand verbena, silver beachweed, saltgrass, miniature lupine, plantain, and sand-dune bluegrass.|
|Threats||Soil damage; habitat alteration and herbivory by cattle, elk and deer; damage by vehicles.|
Gilia tenuiflora ssp. hoffmannii (Hoffmann's slender-flowered gilia) was described by Eastwood in 1940 from collections made by Hoffmann ten years earlier "in sandy soil at East Point" on Santa Rosa Island. Eastwood remarked that, although the taxon is related to G. tenuiflora, no variation of the latter included the leafy stems and terminal congested inflorescence of G. hoffmannii. Nevertheless, Jepson in 1943 included the taxon in the description of G. tenuiflora var. tenuiflora in his flora of California, as did Abrams in his flora of the Pacific states. In 1959, Munz included the varieties of tenuiflora as subspecies, including ssp. hoffmannii, as per a 1956 treatment by the Grants. This nomenclature was used in the latest treatment of the genus. Of the four subspecies of G. tenuiflora, the subspecies hoffmannii is the only one that occurs in southern California. Two other Gilia species occur on Santa Rosa Island, but G. tenuiflora ssp. hoffmannii is distinguished from them by the presence of arachnoid woolly pubescence at the base of the stem.
G. tenuiflora ssp. hoffmannii is a small, erect annual herb in the phlox (Polemoniaceae) family. The central stem grows 2.4-4.7 in (6-12 cm) tall, arising from a rosette of densely hairy, strap-shaped, short-lobed leaves. The flowers are purplish and funnel-shaped below, widening to five pinkish corolla lobes.
G. tenuiflora ssp. hoffmannii occurs at the East Point locality of Santa Rosa island as a component of dune scrub vegetation with sand verbena (Abronia maritima ), silver beach-weed (Ambrosia chamissonis ), saltgrass (Distichlis spicata ), miniature lupine (Lupinus bicolor ), plantain (Plantago erecta ), and sand-dune bluegrass (Poa douglasii ).
G. tenuiflora ssp. hoffmannii historically has only been collected from two locations on Santa Rosa Island. A collection was made by Reid Moran from the "arroyo between Ranch and Carrington Point" in 1941. Rindlaub located a population of 88 individuals covering 21 sq ft (2 sq m) in 1994, a location that reasonably corresponds to Moran's site and is grazed by cattle. The other historical location is at the type locality near East Point on Santa Rosa Island, where the plant is still found in a population of about 2,000 plants. During 1994 surveys, a third population comprised of three colonies was found at Skunk Point. This population of approximately 3,000-3,500 individuals that had been obviously grazed by cattle.
G. tenuiflora ssp. hoffmannii is threatened by soil damage, habitat alteration and herbivory by cattle, elk and deer. A sandy service road used by National Park Service (NPS) and ranchers bisects the East Point population. NPS constructed a fence to exclude cattle from a portion of the largest population; however, a considerable portion of the population has had increased trampling by cattle and greater impacts from vehicles as a result of the fence construction and continued use of the road.
Specific examples of browsing or grazing by alien mammals on G. tenuiflora ssp. hoffmannii have been observed. Unfenced portions of G. tenuiflora ssp. hoff-mannii on Santa Rosa Island are areas where cattle concentrate and churn the soil. Of the six collections of Gilia in the herbarium at the Santa Barbara Botanic Garden, only the two collections made during April 1941 show no signs of browsing. The remaining four collections, made between 1963 and 1978 from the months of May and June, show signs of having been browsed. One Gilia population was visited twice in 1993; during the first visit in April, the Gilia had not been browsed, but by the second visit in May the Gilia had been browsed. In response to such browsing, the annual Gilia forms multiple side branches, and although a branched plant may produce a greater number of flowers, this does not necessarily increase the fecundity of the plant. Flowers produced later in the season out of synchrony with pollinator activity results in lower seed productivity.
Compaction of soils and crushing of plants by vehicle traffic is an ongoing threat to G. tenuiflora ssp. hoffmannii. The largest population of G. tenuiflora ssp. hoffmannii is bisected by a road. Another road continues to damage habitat and plants along the fence line established to protect the western snowy plover; however, the proposed closure of Old Ranch Pasture to cattle and horses will remove the necessity to maintain a fence at that location.
Conservation and Recovery
The Hoffmann's slender-flowered gilia only survives as three populations on Santa Rosa Island. This island has been owned by the NPS since 1986, but a private cattle ranching operation and a subleased deer and elk hunting operation are operating under special-use permits, renewable until 2011. Feral pigs are not part of this agreement, and the NPS has eradicated these animals from the island. However, the Santa Rosa Island manzanita and other rare plants remain severely threatened by the feeding of introduced mammals and associated factors. The survival of this endangered plant requires strict protection from the feeding of mammals. Until the special-use permits expire, this could be done by securely fencing the plants. After the permits expire the introduced mammals should be eradicated from the critical habitat. The populations of the Hoffmann's slender-flowered gilia should be monitored, and research undertaken into its biology and ecological requirements. It should be propagated in captivity, to supply stock for out-planting to supplement the small wild population.
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