Leaves broad and flat, never needle-like or scale-like, simple, opposite
or whorled.
1. Leaves (or some of them) in whorls of 3.
2. Leaves with a bad odor when crushed; flowers with conspicuous
purple spots _Catalpa bignonioides_
2. Leaves without a bad odor when crushed; flowers merely lined with
purple _Catalpa speciosa_
1. Leaves opposite.
3. Leaves at least 6 inches long and 6 inches broad, heart-shaped at
the base, never palmately lobed _Paulownia tomentosa_
3. Leaves usually less than 6 inches long and 6 inches broad, not
heart-shaped at the base or, if slightly heart-shaped, then also
palmately lobed.
4. Leaves palmately lobed.
5. Leafstalk with milky sap when broken _Acer platanoides_
5. Leafstalk without milky sap.
6. Areas between leaf lobes mostly V-shaped; leaves usually
silvery or white on the lower surface.
7. Leaves deeply divided, the areas between the lobes
extending more than half-way to the midvein
_Acer saccharinum_
7. Leaves shallowly divided, the areas between the lobes
extending less than half-way to the midvein.
8. Leaves completely covered with a white felt on the
lower surface _Acer rubrum var. drummondii_
8. Leaves smooth or sparsely hairy on the lower leaf
surface _Acer rubrum_
6. Areas between leaf lobes mostly U-shaped; leaves green or
paler on the lower surface, not white or silvery.
9. Leaves with the edges drooping.
10. Leaves green on the lower surface; small leafy
outgrowths sometimes present at the base of the
leafstalk _Acer nigrum_
10. Leaves grayish on the lower surface; small leafy
outgrowths at the base of the leafstalk absent
_Acer barbatum_
9. Leaves flat, the edges not drooping _Acer saccharum_
4. Leaves not lobed.
11. Leaves toothed along the edges.
12. Edges of leaves regularly toothed from tip of leaf to
base; leaves usually short-pointed or rounded at the tip.
13. Buds, leafstalks, and veins on the lower surface of the
leaf covered with rusty hairs _Viburnum rufidulum_
13. Buds, leafstalks, and veins on the lower surface of the
leaf without rusty hairs.
14. Leaf stalks wavy along the edges _Viburnum lentago_
14. Leaf stalks not wavy along the edges.
15. Branches spine-tipped _Rhamnus cathartica_
15. Branches not spine-tipped _Viburnum prunifolium_
12. Edges of leaves toothed only above the middle of the leaf;
leaves tapering to a long point _Forestiera acuminata_
11. Leaves not toothed along the edges.
16. Upper surface of leaves rough to the touch
_Cornus drummondii_
16. Upper surface of leaves smooth.
17. Leaves with deeply impressed veins on the upper surface;
lower surface of leaves gray or whitish.
18. Leaves often nearly as broad as long; flowers
surrounded by 4 large, white bracts; berries red;
twigs green _Cornus florida_
18. Leaves longer than broad; flowers not surrounded by 4
large, white bracts; berries white; twigs gray
_Cornus racemosa_
17. Leaves without deeply impressed veins; leaves often
paler on the lower surface, but not gray or whitish
_Forestiera acuminata_