This tall perennial is widespread on damp fertile soils across northern and western regions of North America, and it is closely related to the Eurasian H. sphondylium L. ("hogweed" or "cow parsnip"). Plants of the sphondyllum complex are locally common across the Northern Hemisphere in diverse types of disturbed submesic eutrophic openings within borea/subalpine and cool temperate woodland. Shoots have had much nutritional and medicinal use by herbivorous and omnivorous mammals, including "Heraclesian" humans (e.g., Bank 1953, McLellan & Hovey 1995, Webster et al. 2006, Matarrese & Massimiliano 2023). Deterrant fumarocoumarins are much less concentrated than in the invasive aliens, H. mantegazzianum Sommier & Levier ("giant hogweed") and Pastinaca sativa (wild parsnip). H. maximum extends south at higher elevation into the Southern Appalachians and into the upper Midwest, with a few records close to Ky. in s. Ohio and s. Ill. (K). In Ky. it known from only a few scattered disjunct sites. There are recent colls. from bottomlands along the Ohio River: by R. Gelis from Manchester Islands in LEWI (BEREA; Abbott et al. 2004); and by E. Hartowicz (pers. comm.) and others from the South Shore WMA in GRNP. There are older records from mesic to subxeric woods on Black Mountain (including Benham Spur), which still need deserve further investigation (M). There are also uncertain western records attributed to CHRI (C.W.Short coll. at PH) and the Cumberland River bottom in TRIG (W.L. Thomas 1968: Univ. of Louisville M.Sc. thesis cited in M). H. maximum is known from adjacent Stewart Co. in w. Tenn. (Ch).