Root Parasitism in Schoepfia Schreb. (Olacaceae)

Abstract

Hemiparasitism is documented in a species of the Olacaceous genus Schoepfia. Excavation of plants of S. schreberi from Florida and the Bahamas revealed numerous haustoria of a more or less conical shape and up to 4.5 mm in width, possessing what appear to be numerous collapsed layers at an early stage. Ten hosts from eight different families have been identified, and, as is the case with most phanerogamic root parasites, it appears that S. schreberi lacks host specificity. This report brings to five the number of known parasitic genera of the Olacaceae, a family of some 35 genera. THE EXTENT TO WHICH PARASITISM OCCURS among members of the Olacaceae, an exclusively tropical family, is unknown. Of the 35 genera in this family ( Bentham and Hooker 1862), Kuijt (1969) lists only four in which parasitism has been documented (Cansjera, Olax, Ptychopetalum, Ximenia). Ximenia americana L. is fairly common in southern Florida and has been the subject of several studies pertaining to its life cycle and parasitism (Heckel 1900, Barber 1907, DeFillips 1969, Mlusselman and Mann 1977). The only other genus of Olacaceae occurring in North America is Schoepfia, represented in the United States by S. schreberil J. F. Gmel., which is known by the common names whitewood and gulf graytwig. Schoepfia schreberi is a small tree or shrub found in pinelands, hammocks, and coppets (fig. 1), and it ranges over southern Florida, the West Indies, and Central and South America (Long and Lakela 1976). In Florida, it is much rarer than Ximenia. Although Long and Lakela (1976), in their description of Schoepfia, state that it is reported as parasitic on roots, we have been unable to discover any documentation of parasitism for this genus. Schellenberg (1932) stated that Schoepfia is undoubtedly parasitic because it possesses reduced ovules, but he did not offer direct evidence. Likewise, Reed (1955), without reference or evidence, attributed root parasitism to the tribe Schoepfiae consisting only of Schoepfia. The following is a report of our observations of haustorial attachments by the roots of S. schreberi to those of neighboring plants. MATERIALS AND METHODS The populations studied were located on Andros Island, Bahamas, and in Melbourne, Florida, U.S.A. (see table 1), and observations were made during the summers of 1975 through 1977. The Andros Island population comprised six small trees with their roots embedded in limestone. Excavation involved a careful chiselling away of the rock to expose the main roots which were then traced to their branches. The Florida population consisted of five large trees (up to 6 m) scattered throughout a live oak-palmetto palm hammock. The soil at this location was sandy, and excavation was not as difficult. Voucher specimens of S. schreberi and of host plants from the Andros Island population have been deposited in the herbaria of Miami University (MU), Oxford, Ohio, and Old Dominion University (ODU), Norfolk, Virginia.