This southeastern species has sometimes been confused with imbricaria; and further south with Q. laurifolia Michx. [Q. laurifolia is reported from ne. Ark. and may occur in w. Tenn. within 20 miles of Ky.; it is rarely cultivated in Ky.]. Occasional hybrids of phellos have been reported with those two species, also with pagoda, velutina, palustris and other species (FNA 3); but only a few hybrids have been indicated in Ky. (with velutina and perhaps rubra). Further verification of phellos is needed in several counties. Old reports from n. Ky. remain dubious (Gm). There has been widespread planting north of its range for urban use and for reforestation of wetlands (e.g. on Salt Rv. bottoms along US 62 in NELS). Although seedlings occasionally establish from these planted trees (e.g. MADI at BEREA; see also K), these records are not mapped here. Several trees have been recently appeared to be native in a wetland of BATH near Cave Run Dam (K. Feeman and A. Risk, pers. comm.), but there has been a history of plantings on federal lands around the lake. The potential for long-distance dispersal by waterfowl is intriguing. As a native plant, phellos is often restricted to small peripheral remnants of swampy woodland that experience seasonal drought or disturbance. Planted trees in central or northern Ky. are often tardily deciduous, with mostly green leaves remaining until mid-Nov (or in a few trees even early Dec of 2018); imbricaria can also be relatively late to drop leaves, but in a less green condition. Q. phellos has the smallest acorns among oaks of Ky., with nuts 8-12 x 6.5-10 mm. In general the red oaks of more open, stressed, xeric or hydric sites have relatively small acorns: with nuts mostly 9-16 x 8-16 mm. In contrast, nuts of rubra, shumardii, texana, coccinea and velutina are 12-30 x 10-21 mm.