The Distribution of Thelypteris torresiana in the Southeastern United States

Abstract

Near the turn of this century Thelypteris torresiana (Gaud.) Alston, a fern new to the United States, was collected in Seminole County, Florida. Small (1938) mentions that it was first collected in Florida by T. L. Mead about 1906; however, a specimen of this taxon collected by A. A. Eaton, dated May 1904, is among the collections at the United States National Herbarium. Both the Mead and Eaton collections came from the vicinity of Oviedo in Seminole County, and on the label of the Eaton specimen a note was added that the plants were escapes from cultivation. Although the early collections were identified as Dryopteris setigera (Blume) Kuntze, the nomenclatural status of this fern has been clarified by Morton (1962), Ching (1963), Reed (1968), Holttum (1969), and others. True Dryopteris setigera is a rare Asian species, probably neither cultivated nor naturalized in the New World. The American collections, erroneously identified as Dryopteris setigera, are Thelypteris torresiana, a combination made by Alston in 1960 based on Guadichaud-Beaupre's Polystichum torresianum from Guam. In a recent study of Old World species of Thelypteris sensu lato, Holttum (1969) maintains the combination Macrothelypteris torresiana (Gaud.) Ching in his revision of the Thelypteridaceae. Until knowledge of this family is further refined, I have followed a more conservative generic treatment. After 1904-1906, when the first collections of Thelypteris torresiana were made in Florida, there were no additional reports of this fern from the southeastern United States until it was located in Polk County, Florida in 1922. A few years later it turned up in Volusia County (1924) and in Manatee County (1926), both in central penisular Florida. Another ten years elapsed before it was recorded for Highlands and Orange Counties, Florida. In 1938, Small wrote that it was appearing spontaneously in many remote localities and in great abundance. The first record of the occurrence of Thelypteris torresiana in a state other than Florida was in 1948, when L. C. Crawford located a population in Conecuh County, Alabama. A few years later it was reported from the Coastal Plain of Texas (Newton County) by Correll (1951). It seems likely that by this time T. torresiana would have been present also in southern Georgia, southern Mississippi, and Louisiana, although stations in these states were not discovered until 1959, 1961, and 1968, respectively.