Rhodobryum ontariense is a dendroid moss that occurs both as a facultative epilith and as a facultative epiphyte. A few studies have addressed its chemical constituents, but almost none have examined its ecological characteristics, even though it is a common and characteristic species of eastern deciduous forests. We collected data on substrate, patch size, chlorophyll content, overstory trees, and associated bryophytes of R. ontariense at three sites in western North Carolina: the Big Ivy area of Pisgah National Forest, Catawba Falls, and Dupont State Forest. Rhodobryum ontariense occurred mostly on rocks at Catawba Falls, mostly on trees at Dupont Forest, and nearly equally on rocks and trees at Big Ivy, where patch size did not differ between substrates. Epiphytic patches occurred most often on Liriodendron tulipifera and Quercus alba, and trees hosting epiphytic patches tended to be larger in diameter than trees nearest to epilithic patches. We documented 28 species of associated bryophytes, including 25 mosses and three liverworts. Eleven species (including all three liverworts) were only on rocks, eight were only on trees, and nine were on both rocks and trees. Only five species occurred at all three sites, including Thuidium delicatulum, which was the most common associate on both substrates, followed by Anomodon attenuatus. Chlorophyll levels did not differ between epilithic and epiphytic R. ontariense, suggesting that photosynthetic capacity was similar on both substrates.