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The inclusion of the filmy fern Trichomanes petersii Gray in the Louisiana flora was previously based on a 1924 collection from near Covington in St. Tammany Parish (Brown & Correll, 1942). I am reporting seven new locations for this fern in Louisiana. Throughout most of its range, T. petersii grows on rocks or soil and is rarely reported as an epiphyte. But in all Louisiana locations, it was epiphytic. I found T. petersii on Southern Magnolia (Magnolia grandiflora L.) and on American Beech (Fagus grandifolia Ehrh.). On American Beech the fern usually occurs as a small population (ca. 25 cm2 or less) very close to the ground, usually on the buttress sides. On Southern Magnolia it usually forms large populations (ca. 900 cm2 or more) and is 3-10 dm above the base of the tree. In one location, the fern was about 3.5 m above the tree base. Southern Magnolia seems to be the preferred habitat; I have found 10 populations on it but only five on American Beech.