Cucurbita okeechobeensis ssp. okeechobeensis
|Listed||July 12, 1993|
|Description||Annual, fibrous-rooted, high-climbing vine with tendrils, heart-to-kidney shaped leaf blades and bell-shaped cream-colored flowers.|
|Habitat||Heavy, tangled canopy of the shores of Lake Okeechobee, Florida Everglades.|
|Threats||Lowering of the lake level, construction of water management facilities, intrusion of other plants.|
The Okeechobee gourd is an annual or perennial, fibrous-rooted, high-climbing vine with tendrils, belonging to the gourd family (Cucurbitaceae). The Okeechobee gourd possesses heart-to kidney-shaped leaf blades, with five to seven angular, shallow lobes, and irregularly serrated margins. Young leaves are covered with soft hairs. The cream-colored flowers are bell shaped, with the corolla 2.3-2.7 in (6-7 cm) long. They can be distinguished from flowers of Cucurbita martinezii (the Martinez gourd) by the presence of dense pubescence on the hypanthium of the male flower and on the ovary of the female flower. The light Okeechobee green gourd is globular or slightly oblong, with 10 indistinct stripes, and hard shelled with bitter flesh. The seeds are gray-green and flat. The stems produce adventitious roots at the nodes and will separate from the parent plant if they contact soil or water.
Closely related gourds with cream-colored corollas (all others in the genus Cucurbita are bright yellow) are found in Florida and in Mexico, near the Gulf coast.
The Florida plants were described as the Okeechobee gourd and the Mexican plants were designated as the Martinez gourd. The flowers usually open in the early morning. Although pollinators have not been identified, based on closely related gourds, a variety of insects are likely to be available, including bees, flies, and squash beetles, and pollination is not considered to be a limiting factor.
The seeds germinate in early spring during the dry season, when the lake level is low. Seedlings do not tolerate water-soaked soil for extended periods, which would account for the discovery of a stand of Okeechobee gourds apparently in decline, inundated in 8-12 in (20-30 cm) of water. By the rainy season, the vines will have climbed shrubs, avoiding complete inundation as the lake rises. The vines and fruit become most visible by early to mid-summer.
Although the exact mechanism for seed dispersal of the Okeechobee gourd is unknown, the Okeechobee gourds seem to disperse by floating in canals and along the shore of islands in Lake Okeechobee; marsh rabbits may be the main terrestrial dispersal agent. No information is available on dispersal distances for floating gourds in Lake Okeechobee.
The Okeechobee gourd relies on pond apple trees to support its vines above rising water levels during the wet season. Other trees and shrubs, such as willow and cypress, may also provide suitable support for the vines.
The Okeechobee gourd seems to readily germinate on alligator nests in Lake Okeechobee, which provide suitably elevated soil berms in full sun, with no competition from other plants. Although alligators do not typically construct nests in woody vegetation, they do clear herbaceous vegetation, sometimes close to shrubs and trees. After gourds germinate on the cleared ground around the nest, they begin to grow prostrate. If trees or shrubs are present nearby, the gourd plants will eventually climb. Alligators, though, do not seem to be important to the survival of the gourd in the St. Johns River.
Marsh rabbits gnaw on green gourds and take pieces to their nests, which suggests that marsh rabbits are important to terrestrial dispersal of the gourd. Because many insect species have evolved with specific cucurbits, the Okeechobee gourd could be a keystone species for some, as yet unidentified, pollinator. Both the Floridian and Mexican sub-species of C. okeechobeensis are highly resistant to many diseases that threaten economically valuable plants, with the Martinez gourd currently used as a source of disease resistance for summer squash, pumpkins, and gourds.
The documented population of the Okeechobee gourd around the southeastern shore of Lake Okeechobee is strongly associated with Torry muck, a soil formed in the extensive pond apple forests that once surrounded Lake Okeechobee. Successful growth and reproduction of the gourd under cultivation, however, suggests that the species can grow in a wider range of soils.
The gourd seems to need the natural trellises of pond apple branches. Nevertheless, the gourd readily climbs any plant that will provide a trellis; in both Lake Okeechobee and the St. Johns River, the Okeechobee gourd grows on elderberry and buttonbush, which in turn are associated with alligator nests.
For the gourd to maintain viable healthy populations, fluctuations in lake level are necessary. High lake levels facilitate dispersal and inundate and destroy aggressive weeds in local habitats. As lake levels decrease, the cleared open habitats allow the quickly germinating Okeechobee gourd seeds to sprout and begin climbing before they have to compete with other pioneer species.
The Okeechobee gourd was found on the southern shore of Lake Okeechobee, in Palm Beach County, and formerly in the Everglades. The relative abundance of the Okeechobee gourd in the Everglades region south of the extent of the original pond apple forest along the southern rim of Lake Okeechobee is not known. In 1965, it was seen north of Homestead in an agricultural area of Dade County. A population on a disturbed roadside north of Andytown, Broward County, was discovered in 1978 and was destroyed by road construction the following year.
In late twentieth century surveys, the species was found to be restricted to nine sites along the middle St. Johns River in Volusia County and 11 sites along the southeastern shore of Lake Okeechobee, including Torry Island, Ritta Island, Kreamer Island, Bay Bottom Dynamite Hole Island, South Shore Dynamite Hole Island, and the southern shore of the Lake Okeechobee Rim Canal.
The Okeechobee gourd persisted around Native American villages with the Seminole pumpkin, C. moschata, which is edible. The Okeechobee gourd's bitterness precluded its use for food. It may, however, have been used as a ball, rattle, or ceremonial cup. It was observed and/or collected in 1913 and 1917 and found to be locally common in the remnant pond apple forests surrounding Lake Okeechobee. At least 95% of this habitat had already been destroyed by 1930. After 1930, the Okeechobee gourd was observed infrequently. In 1941 it was found on Observation Island in Lake Okeechobee, Glades County. Surveys were unable to relocate the Okeechobee gourd there in 1984 or 1987. In 1981 the Okeechobee gourd was found in some lake, levee, and canal bank areas at Kreamer and Torry Islands. G. P. Nabhan's 1988 search only turned up three gourds, and no live plants. Seeds from the gourds Nabhan found were planted at Bok Tower Gardens, Florida, where the plant currently thrives under cultivation.
A new population of the Okeechobee gourd was found along the shore of the middle St. Johns River in September 1993. Gourds had not been noted in this area for more than 200 years. Upon further investigation, a total of nine sites were located in Volusia County on the middle St. Johns River.
Because the Okeechobee gourd flourishes when suitable soils are exposed during low water levels, the best time to survey for the species is during moderate or severe drought. The most recent surveys were conducted during drought conditions in 1990 and 1991. The species was found at a total of 11 sites along the southeastern shore of Lake Okeechobee, including Torry Island, Ritta Island, Kreamer Island, Bay Bottom Dynamite Hole Island, South Shore Dynamite Hole Island, and the southern shore of the Lake Okeechobee Rim Canal. Water levels were high in 1994-1996, and no organized searches for the species were conducted around Lake Okeechobee in the late 1990s.
It is important to remember that gourds are ephemeral by nature; they can appear at a site for one or many years and then disappear from that site. Because of the rambling growth habit of the gourd, and because plants can root at the nodes, it is difficult to count numbers of individual plants. Counting the number of fruits on the vines in the fall may provide a good index of the reproductive health of the population, rather than attempting to count individual plants.
The plant's decline is largely attributable to two factors: conversion of swamp forests to agriculture and water level management in Lake Okeechobee. Agricultural conversion was the principal form of habitat destruction for the gourd prior to 1940. During the early twenty-first century, water management practices appear to be the greatest threat. Permanent inundation of suitable soils is detrimental to the species. Water regulation practices can greatly influence the timing and duration of flooding and drying cycles across remnant areas of suitable elevation and soils around Lake Okeechobee
Because the Okeechobee gourd has been found growing along the edges of canals, and because herbicides are routinely applied around Lake Okeechobee to keep aquatic weeds from choking the waterways, aquatic vegetation management practices should be modified to ensure compatibility with recovery of the species.
Another potential threat to this plant is the proliferation of exotic plant species around the edges of Lake Okeechobee, particularly Melaleuca. Although scattered Melaleuca trees may provide suitable support for climbing gourd plants, Melaleuca stands generally become a dense monoculture. Densely shaded areas in the center of Melaleuca stands are not suitable for the Okeechobee gourd. Control of aquatic weeds can involve spraying from airboats or airplanes, but Melaleuca control can be accomplished by cutting and squirting herbicide into individual tree trunks. Melaleuca control is a necessary management practice to prevent degradation of littoral zone habitat quality for a variety of animals and plants in Lake Okeechobee, including the Okeechobee gourd; the controlled use of herbicide applied directly to Melaleuca trees is not likely to have an adverse effect on the Okeechobee gourd.
The extensive pond apple forest that once surrounded the southern shore of Lake Okeechobee most likely supported a stable core population of the gourd, allowing the long-term survival of the species despite year-to-year changes in peripheral sites that became temporarily available or unavailable in response to natural water fluctuations.
Conservation and Recovery
Aside from regulation of collecting and interstate trade, management for this endangered plant is mostly nonexistent. Habitat modification and enhancement should include the control or extirpation of exotic pest plants such as Melaleuca and Brazilian pepper in specific areas where the Okeechobee gourd is known to grow. These exotics should be replaced with pond apple or other appropriate native woody vegetation to provide potential vine-supporting vegetation. A variety of factors related to water storage, flood control, and navigation, and ecological concerns (waterfowl, fisheries, littoral zone vegetation, water quality, snail kite recovery, and others) can potentially conflict. A balance must be found among these competing interests that will promote recovery of the Okeechobee gourd. Spraying of herbicides to control growth of aquatic vegetation should be avoided or strictly controlled in areas where habitat is being managed for recovery. Experimentation is needed to test how sensitive the Okeechobee gourd is to the chemicals currently being used. Depending on the results of that experimentation, aerial spraying may need to be prohibited in areas where the species grows. For boat-based spraying, an out-reach program is needed to educate spraying crews to recognize the Okeechobee gourd and avoid spraying the plants. If spraying is unavoidable, the least vulnerable period for the Okeechobee gourd may be November and December, after plants have fully developed fruit and before seedlings emerge.
The primary technique for control of woody exotic vegetation should be application of herbicide to individual trees wherever practical, while aerial spraying should be used with great caution and only on large Melaleuca heads adjacent to the Lake Okeechobee rim canal.
Recovery of the Okeechobee gourd may require special emphasis on protection and management of Ritta Island. This is the only site in Lake Okeechobee with what appeared to be more mature plants. Plants at other sites around the lake appeared to be in poor health and transitory. Lacking the large pond apple forest that likely served as a stable reserve bank of plants, Ritta Island is now the likeliest among the sites identified in 1991 to be persistent. Information is lacking, however, on how well the plants survived several years of high water levels during the 1990s. Dense growth of Colocasia appears to be blocking free dispersal of fruits at Ritta Island. Rather than attempt to remove or control Colocasia, it may be more effective to intervene by dispersing the seed according to a management plan.
The relationship of fire and the Okeechobee gourd is also not fully understood. Fire could be a threat in that it could destroy plants, yet it could also be a management tool because gourds sprout in areas cleared by disturbance. More frequent and more thorough surveys for the plant may reveal a pattern of response to fire.
The introduction of plants to sites within and outside of Lake Okeechobee seems feasible. Within the lake, Observation Island and Little Rocky Island should first be more thoroughly searched to see if the Okeechobee gourd is present. If not, these islands are good candidates for introduction. Public lands should be identified along the Kissimmee River with suitable environmental conditions for introduction of the species. Because the species now occurs in two widely separated populations, Lake Okeechobee and St. Johns River, establishment of a third population between the two existing populations is considered a desirable safeguard against extinction, particularly with respect to catastrophes, such as hurricanes.
Other potential recovery actions would involve physical alteration of the environment, either removal of levees or mounding of organic material to provide substrate at appropriate elevations. It is unclear at this time whether degrading the levees at Torry and Ritta Islands would promote recovery of the Okeechobee gourd. Improved water flow through these areas may promote dispersal of fruits. Mounding of organic soil on Torry and/or Ritta Islands could be part of a restoration plan for those islands and could provide a safeguard against prolonged periods of high water. Roads are present on both islands, making access of earthmoving equipment more practical. Additional contaminant sampling may be necessary on both islands to ensure that residue from previous application of agricultural chemicals does not preclude moving these sediments. Another possibility is mounding of organic berms that have built up in an area southwest of Buckhead Ridge. The latter project, however, would require water levels in the lake be held down around 13 ft (4 m) and may present logistical problems in terms of access and operation of machinery, which would tend to get stuck.
Water management practices in Lake Okeechobee affecting the Okeechobee gourd are also likely to affect the wood stork and the snail kite. The hydrologic requirements for the three species are not mutually exclusive, however. All three species are adapted to withstand periods of drought and high water, but prolonged periods of three or more successive years at either extreme might be adverse to their survival. The snail kite temporarily benefits from periods of high water, but prolonged periods would drown out woody vegetation needed by kites as nesting substrate. Extended periods of high water for several continuous years may jeopardize the Okeechobee gourd, because the seeds would not germinate and young plants cannot tolerate deep water. On the other hand, the gourd might temporarily benefit from drought conditions, because low water provides more suitable habitat within the Herbert Hoover Dike surrounding Lake Okeechobee. But extended periods of low water could favor dense stands of woody vegetation, which would not be favorable to the gourd or the overall productivity of Lake Okeechobee. More research is needed on fluctuations in abundance of the gourd in response to water conditions, particularly extended periods of high water, to determine the level of risk to the long-term survival of the species.
U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
1875 Century Blvd., Suite 200
Atlanta, Georgia 30345
U. S. Fish and Wildlife Service
Jacksonville Ecological Services Field Office
6620 Southpoint Dr. S., Suite 310
Jacksonville, Florida 32216-0958
Telephone: (904) 232-2580
Fax: (904) 232-2404
Minno, M. C., and M. Minno. 1995. "Status and Habitat Requirements of the Endangered Okeechobee Gourd along the Middle St. Johns River, Florida." Report. Submitted to U. S. Fish and Wildlife Service; Jacksonville, Florida.
Nabhan, G. P. 1989. "Lost Gourds and Spent Soils on the Shores of Okeechobee." In Enduring Seeds. North Point Press, San Francisco.
U. S. Fish and Wildlife Service. July 12, 1993. "Endangered or Threatened Status for Five Florida Plants." Federal Register 58 (131).
Walters, T. W., and D. S. Decker-Walters. 1993. "Systematics of the Endangered Okeechobee Gourd, C. okeechobeensis. " Systematic Botany 18 (2): 175-187.
Walters, T. W., D. S. Decker-Walters, and S. Katz.1992. "Seeking the Elusive Okeechobee Gourd." Fairchild Tropical Garden Bulletin 47 (1): 23-30.