1 Leaf blades mostly < 7 cm long, the base symmetrical to somewhat oblique.

  2 Samaras ciliate-margined; twigs often cork-winged; upper surfaces of leaves glabrous to scabrous; petioles 1-3 mm long; [native, sometimes weedy]; [subgenus Oreoptelea, section Chaetoptelea].

    3 Leaf apex acute; flowers appearing in the late winter to late spring; calyx lobes 5, broadly rounded; upper surfaces of leaves glabrous to somewhat scabrous; [widespread in our area]

    3 Leaf apex obtuse; flowers appearing in the late summer to fall; calyx lobes 6-9, linear; upper surfaces of leaves harshly scabrous; [w. TN and w. MS westward; disjunct in FL]

  2 Samaras with glabrous margins; twigs never cork-winged; upper surfaces of leaves glabrous; petioles 2-8 mm long; [introduced, planted and sometimes naturalized or persistent].

      4 Flowers appearing in the late summer to fall; leaf base generally oblique; leaves 1.5-2.5 cm wide, 5 or more of the lateral veins forked per side; bark of trunks irregularly platy with smooth, flattened plates, exfoliating to reveal lighter-colored areas beneath plates; leaf margins singly serrate-crenate (the teeth rather rounded); [subgenus Ulmus, section Microptelea].

      4 Flowers appearing in the late winter to late spring; leaf base generally symmetrical; leaves 2-3.5 cm wide, 3 or fewer of the lateral veins forked per side; bark of trunks deeply ridged and furrowed; leaf margins sharply doubly serrate (the teeth acute-acuminate); [subgenus Ulmus, section Foliaceae]

1 Leaf blades mostly > 7 cm long, the base moderately to strongly oblique (rarely nearly symmetrical).

        5 Leaf uppersurface slightly to very strongly scabrous; leaf undersurface tomentose or villous, with tufts of hairs in the vein axils; flowers and fruits sessile or subsessile (on pedicels 0-2 mm long), in dense non-pendulous fascicles.

          6 Leaves with ciliate margins; samara pubescent on the body with reddish hairs; bud scales red, the margins red-tomentose; [native]; [subgenus Ulmus, section Ulmus]

          6 Leaves without ciliate margins; samara glabrous except along the margin of the notched apex or on the central vein of the wing; bud scales brown, margins pale-ciliate; [introduced, planted and sometimes naturalized or persistent]

             7 Leaf base strongly oblique, the lower side overlapping the petiole; branchlets not corky; samara glabrous except on the central vein of the wing; [subgenus Ulmus, section Ulmus]

             7 Leaf base oblique but not overlapping the petiole; branchlets with corky wings; samara glabrous except along the margin of the notched apex; [subgenus Ulmus, section Foliaceae]

        5 Leaf uppersurface glabrous (or slightly to moderately scabrous, especially on stump sprouts or seedlings); leaf undersurface glabrous to tomentose, with or without tufts of hairs in the vein axils; flowers and fruits pedicellate (on pedicels 5-20 mm long), pendulous, in fascicles or racemes.

               8 Leaf undersurfaces glabrous or slightly pubescent, but always with tufts of hairs in the vein axils; branches never with corky wings; inflorescence a fascicle; [widespread in our area]; [subgenus Oreoptelea, section Blepharocarpus].

                 9 Leaf bases moderately oblique (rarely nearly symmetrical); larger leaves 7-10 cm long; primary leaf teeth acute, not curved; [moist calcareous sites in the Coastal Plain from se. NC southwards]

               8 Leaf undersurfaces moderately white or yellowish soft-pubescent, lacking prominent tufts of hairs in the vein axils (differing from the general pubescence of the surface); branches often developing corky wings; inflorescence a raceme or racemose cyme; [calcareous areas west of the Blue Ridge (w. PA, WV, KY, e. TN, nw. GA, and AL westwards)]; [subgenus Oreoptelea, section Chaetoptelea].

                   10 Leaves 7-8 (-14) cm long, lanceolate to ovate, the undersurface with yellowish-gold pubescence; buds and young twigs glabrous; calyx lobes 5-6; seeds thickened

                   10 Leaves 9-11 (-16) cm long, obovate, the undersurface with whitish pubescence; buds and young twigs pubescent; calyx lobes 7-8; seeds inflated