Two Species of Adiantum Newly Escaped in Florida

Abstract

Adiantum trapeziforme L. was discovered by the late George N. Avery in February 1980. He found a single plant growing at the top of a low spoil bank in an area kept humid by runoff from a nearby water-pumping station, and he collected a single fertile frond (Avery 2207, FTG). The fern grows in an area shaded by the exotic weed trees Schinus terebenthifolius and Albizzia lebbeck. Avery took us to see the plant in late 1982; we visited the site again in January 1984. Both times we looked for evidence of young Adiantum plants. No sporelings were ever found, although the original plant appears to be growing well and produces spores regularly. The Adiantum might represent a persistent plant from cuttings dumped at the site, but, as no evidence for dumping was found, we concluded that the plant is a true escape. The future of this species in South Florida is problematical. It grows in a relatively protected area and is not likely to be destroyed by human activities in the near future, but it apparently has not spread in the four years since its discovery. Whether it is capable of becoming truly naturalized is not clear. In March 1983 the senior author found approximately seven plants of Adiantum anceps Maxon & Morton growing on the vertical walls of trenches cut into rocky ground, along with Ctenitis sloanei (Poeppig ex Sprengel) Morton. The plants were growing in the shade of Schinus terebenthifolius. Undoubtedly water collecting at the bottom of the trenches helped maintain a humid environment. Two voucher specimens have been collected (Herndon 702 and Avery 2501, FTG). This species has spread within its rather specialized habitat, suggesting that the climate in South Florida is conducive to its growth. The colony is in an area of active commercial development and will likely be destroyed before the plants spread to more protected areas. Still, the habitat in which the plants grow is quite similar to the pinnacle rock areas found in some Dade County parks. Given the continuous supply of spores from cultivated plants and the availability of apparently suitable habitat in protected areas, it is likely that this species will sooner or later become an established member of our naturalized flora.-Alan and Rhonda Herndon, 15301 S.W. 306th St., Homestead, FL 33033. 29