The original northern limit of this southeastern tree, before Virginian settlement, has been obscured in some recent mapping: compare K with Lifttle (1971). This species has been widely planted in Appalachian regions and locally elsewhere, often outside its native range, as in Mammoth Cave National Park (EDMO, HART) and perhaps Land-Between-the-Lakes (LYON, TRIG). Included here are historical data of Gm, B and Wharton (1945). Not mapped here are western colls. that are probably from planted or escaped individuals; for these, see Cranfill (1991), CW, KY (GRAY, OHIO) and MUR (CALL, MARS). However, there are native trees in w. Tenn. just south of CHRI and TRIG (where the status of some trees remains uncertain). P. echinata was locally abundant in original woodlands of the southern Cumberland Plateau, and it probably increased after initial logging and efforts at clearance on southern Appalachian uplands. Much has died during 1999-2002 due to bark beetles, but a new generation could be fostered by burning of the remaining oak woodland, in order to promote the grassy conditions that allow much regeneration of this pine species. Distinction from taeda, rigida and virginiana is often difficult with leaves alone; better keys need to be developed for use with whole plants in the field (FNA 2, J, W). See notes on hybridization under taeda. There may also be some introgression with rigida (FNA 2, CW), but there is no definite evidence. Although nuclear DNA of echinata indicates a relatively close relationship to taeda, plastid DNA indicates a closer relationship with P. palustris P. Mill. and P. elliottii Engelm. (Gernandt et al. 2018). The state champion is reported from MCRE (KDF 2020): 77 cm dbh, 43 m tall, 17 m wide.