Canelo Hills Ladies'-tresses

Spiranthes delitescens

Description

Canelo Hills ladies'-tresses, Spiranthes delitescens, is a slender, erect, and terrestrial orchid that, when in flower, reaches approximately 20 in (50 cm) tall. Five to ten, linear-lanceolate, grass-like leaves, 7.1 in (18 cm) long and 0.6 in (1.5 cm) wide, grow basally on the stem. The fleshy, swollen roots are approximately 0.2 in (0.5 cm) in diameter. The top of the flower stalk contains up to 40 small white flowers arranged in a spiral. This species is presumed to be perennial, but mature plants rarely flower in consecutive years and, in some years, have no visible above-ground structures.

S. delitescens was first collected in 1968 at a site in Santa Cruz County, Arizona. This specimen was initially identified as S. graminea, a related Mexican species. Spiranthes specimens in Arizona previously thought to be S. graminea displayed a distinct set of morphological and cytological characteristics and was named S. delitescens in 1990.

Habitat

The dominant vegetation associated with Canelo Hills ladies'-tresses includes grasses, sedges (Carex spp.), rushes (Juncus spp.), spike rush (Eleocharis spp.), cattails (Typha spp.), and horsetails (Equisetum spp.). Associated grass species include bluegrass, Johnson grass, Muhlenbergia asperifolia, and M. utilis. The surrounding vegetation is semidesert grassland or oak savannah. All Canelo Hills ladies'-tresses populations occur where scouring floods are very unlikely. Soils supporting the populations are finely grained, highly organic, and seasonally or perennially saturated. Springs are the primary water source, but a creek near one locality contributes near-surface groundwater.

Distribution

This species is known from five sites at about 5,000 ft (1,524 m) elevation in the San Pedro River watershed in the southern Arizona counties of Santa Cruz and Cochise Counties. The total amount of occupied habitat is less than 200 acres (81 hectares). Four of the populations are on private land less than 23 mi (37 km) north of the U. S./Mexico border; one additional small site containing four individuals was discovered on public land in 1996. This site is located near a previously known population. Potential habitat in Sonora, Mexico, has been surveyed but no populations have been found.

As with most terrestrial orchids, successful seedling establishment probably depends on the successful formation of endomycorrhizae, a symbiotic association between plant root tissue and fungi. The time needed for subterranean structures to produce above-ground growth is unknown. Plants may remain in a dormant, subterranean state or remain vegetative (nonflowering) for more than one year consecutively. Plants that flower one year can become dormant, vegetative, or reproductive the next year. The saprophytic/autotrophic state of orchid plants may be determined by climatic fluctuations and edaphic factors, such as pH, temperature, and soil moisture.

Estimating population size and stability of Canelo Hills ladies'-tresses is difficult because nonflowering plants are very hard to find in the dense herbaceous vegetation, and yearly counts underestimate the population because dormant plants are not counted. Individuals in a Canelo Hills ladies'-tresses population were monitored during two-to-three-year periods and found to be stable between 1987 and 1989, but by 1991, one monitored site was reduced to one nonflowering plant. Due to the propensity of Canelo Hills ladies'-tresses to become vegetative for fairly long periods of time and the lack of new flowering plants at one monitoring site, overall population numbers are believed to be declining. Researchers at the University of Arizona who have studied Canelo Hills ladies'-tresses extensively, estimated the total number of individuals in 1996 as less than 5,000, and perhaps less than 2,000.

Threats

Aggressive non-native plants like Johnson grass (Sorghum halepense ) and Bermuda grass (Cynodon dactylon ) disrupt native riparian plant communities. Johnson grass is invading one Canelo Hills ladies'-tresses site, forming a tall, dense monoculture that displaces the less competitive native plants. This Canelo Hills ladies'-tresses population may be lost if Johnson grass continues to spread. Bermuda grass also displaces native riparian plants, including cottonwoods and willows that stabilize stream channels. Bermuda grass forms a thick sod in which many native plants can not become established; in certain microsites, this invasive alien may directly compete with Canelo Hills ladies'-tresses. There are no known effective methods for eliminating Bermuda grass or Johnson grass from natural plant communities on a long-term basis.

Sand and gravel operations remove riparian vegetation and destabilize river banks, shallows, and beds, which could cause Canelo Hills ladies'-tresses population and habitat losses upstream or downstream from the mining. Groundwater has been used since 1983 to wash sand and gravel mined near the Babacomari River, 0.5 mi (0.8 km) west of Highway 90. This activity could affect at least one Canelo Hills ladies'-tresses population.

Reaches of many southern Arizona rivers and streams have been channelized for flood control purposes, which disrupts natural channel dynamics and promotes the loss of riparian plant communities. Channelization modifies the natural hydro-graph above and below the channelized reach, which may adversely affect Canelo Hills ladies'-tresses. Channelization will continue to contribute to riparian habitat decline, and additional channelization will further accelerate the loss and degradation of Canelo Hills ladies'-tresses habitat.

While well-managed recreational activity is unlikely to extirpate Canelo Hills ladies'-tresses populations, severe impacts in unmanaged areas can compact soils, destabilize stream banks, and decrease riparian plant density, including densities of Canelo Hills ladies'-tresses.

Although no specific cases of illegal commercial Canelo Hills ladies'-tresses collecting have been documented, commercial dealers, hobbyists, and other collectors are widely known to significantly threaten natural orchid populations. The commercial value of an orchid already jeopardized by illegal commercial collection may increase after it is listed as threatened or endangered.

Conservation and Recovery

The Canelo Hills ladies'-tresses is known from only five populations, totaling about 200 acres (81 hectares) of habitat. One population is in the Coronado National Forest, and should be protected by ensuring its critical habitat is noted in the management plan for this area and excluded from threatening activities. The other four populations are on private land, and are threatened by various kinds of human influences. These critical habitats should be protected. This could be done by acquiring the land and establishing ecological reserves, or by negotiating conservation easements. The populations of the Canelo Hills ladies'-tresses should be monitored at its known habitats, and searches made to see if there are undiscovered populations, including within potential range in nearby Mexico. Research should be conducted into its biology and habitat needs.

Contacts

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
P.O. Box 1306
Albuquerque, New Mexico 87103-1306
Telephone: (505) 248-6911
Fax: (505) 248-6915
http://southwest.fws.gov/

Arizona Ecological Services Field Office
2321 West Royal Palm Road, Suite 103
Phoenix, Arizona 85021-4915
Telephone: (602) 640-2720
Fax: (602) 640-2730

Reference

U. S. Fish and Wildlife Service. 6 January 1997. "Endangered and Threatened Wildlife and Plants: Determination of Endangered Status for Three Wetland Species Found in Southern Arizona and Northern Sonora, Mexico." Federal Register 62 (3): 665-689.