This has been widely planted (as "Washington thorn") and it occasionally spreads by seed; only apparent wild records are mapped here. It is distinctive, and the only member of series Cordatae; also plants are triploids or tetraploids, whereas others in section Crataegus (monogyna, marshallii, spathulata) are generally diploids, with 2n = 34 (FNA 9). Characteristics include trunk bark flattened to scaly in elongate strips; thorns relatively long (ca. 3-5 cm); leaves relatively large (ca. 3-6 x 2-5 cm), with deltate base and acute to acuminate apex, with prominent veins to major sinuses but not to minor ones between the numerous serrations; flowering relatively late (mostly Jun); and fruits with 3-5 seeds. A hybrid with crus-galli has been reported from cultivation (cultivar "Vaughn"; see missouribotanicalgarden.org), but wild hybrids are virtually unknown. C. phaenopyrum is native from the mid-Atlantic region to the Blue Ridge, and most records further west may be from introductions (D, W; Lance 2006). However, Phipps (1998) and others (F, St) have indicated a broader native range, including the Ozark region and southern Interior Low Plateaus. It appears to be native in Butler Co., Ohio (D. Boone, pers. comm.). Within Ky. some relatively old colls. from western regions suggest native status: e.g. from CALD ("rocky hillsides"), CHRI ("along small streams") at GH; and from LYON and TRIG at APSC. Moreover, the clustering of records in these relatively undeveloped regions supports native status. Much more planting has occurred in more populated areas during recent decades, especially in north-central regions of the states, where escapes have sometimes been found (e.g. as mapped with open dots in FAYE, JESS and MADI).