1 Subshrubs or dwarf shrubs, aboveground stems creeping or erect, < 15 cm tall; leaves evergreen.

  2 Leaves 1.5-3 cm wide, coarsely toothed; flowers lacking sepals and petals; [exotic species, sparingly naturalized or spreading in suburban situations]

  2 Leaves < 1.5 cm wide, finely toothed or entire; flowers with sepals and petals; [native species, collectively widespread and common].

    3 Leaves fleshy, terete in ×-section; petals 5, bright pink

    3 Leaves flat, not fleshy; petals white or pale pink.

      4 Leaves < 2.5 mm wide; corolla with petals distinct; plant creeping

      4 Leaves > 5 mm wide; corolla with petals fused (distinct in Chimaphila); plant creeping or erect

1 Shrubs, aboveground stems erect, > 30 cm tall; leaves evergreen or deciduous.

        5 Inflorescence an involucrate (composite) head subtended by phyllaries, the heads solitary or many and variously arrayed in secondary inflorescences, the ovary inferior, the corolla connate and tubular at least basally, the calyx absent, the stamens 5, the fruit a cypsela

        5 Inflorescence, flower, and fruit structure various, but not with the combination of features as above.

          6 Leaves evergreen. {add to 6a Ardisia in PRIMULACEAE, Rhaphiolepis in ROSACEAE, Camellia in THEACEAE}

             7 Leaves glandular-punctate on one or both surfaces with golden-yellow glands; flowers unisexual, lacking a perianth; fruit a pale gray, waxy drupe with a single seed

             7 Leaves not glandular punctate; flowers bisexual or unisexual, with a white, pink, or yellow perianth; fruit various, a red, blue, or black drupe or berry with several seeds, or a capsule.

               8 Petals connate and urceolate, white to pale pink; flowers bisexual; leaves ovate, lanceolate, or elliptic, broadest near the middle or towards the base, the teeth well-distributed along most of the margin on either side; fruit either a capsule or a red, blue, or black berry

               8 Petals distinct, yellow or white; flowers unisexual or bisexual; leaves oblanceolate or elliptic, broadest towards the tip or near the middle, the teeth usually concentrated in the upper half of the leaf; fruit either a black or red drupe with several pyrenes, a red berry with several seeds, or red or black pomes.

                 9 Plants with nodal, simple or tripartite thorns; flowers bisexual, with a yellow perianth; fruit a red berry with several seeds

                 9 Plants lacking thorns; flowers unisexual or bisexual, with a white perianth; fruit either a black or red drupe with several pyrenes or a red or black pome.

                   10 Flowers unisexual; fruit a black or red drupe with several pyrenes

                   10 Flowers bisexual; fruit a red or black pome

          6 Leaves deciduous {add [Fagaceae]}.

                     11 Plants with nodal, simple or tripartite thorns; leaf teeth spinulose

                     11 Plants lacking thorns; leaf teeth acute, blunt, rounded, or callus-tipped, but not spinulose.

                       12 Leaves crenate-wavy, with 1-2 teeth per cm of leaf margin; leaves usually obliquely cordate or angled-truncate at the base; pubescence of leaves and stems stellate

                       12 Leaves crenulate, serrate or serrulate, with >2 teeth per cm of leaf margin; leaves cuneate, rounded, or subcordate at base, not oblique; pubescence of leaves and stems absent or simple.

                          13 Leaves prominently 3-veined from the base.

                            14 Ovary 5-locular; stamens many or 5, fused or separate; fruit a 5-valved capsule or of 5 mericarps; flowers yellow or pink, or white with a pink blaze

                            14 Ovary 3-locular; stamens 5, separate; fruit a 3-valved capsule or drupe; flowers white or pale green

                          13 Leaves pinnately veined.

                              15 Flowers in catkins; perianth absent or very small; fruit a 1-seeded nut, samara, or waxy drupe (capsule in Salix in SALICACEAE).

                                16 Leaves < 3 cm wide, either punctate-glandular on one or both surfaces or lacking punctate glands; fruit a 1-seeded waxy drupe or a capsule.

                                  17 Leaves punctate-glandular on one or both surfaces; fruit a 1-seeded waxy drupe.

                                  17 Leaves lacking punctate glands; fruit a capsule.

                              15 Flowers arrayed variously, but not in catkins; perianth present, conspicuous; fruit a 1-many-seeded capsule, pome, berry, or follicle.

                                    18 Ovary inferior; fruit fleshy and indehiscent, a berry or pome.

                                       19 Fruit a berry; leaves lacking stipules

                                       19 Fruit a pome; leaves usually prominently stipular

                                    18 Ovary superior; fruit either dry and dehiscent, a capsule or an aggregate of follicles or achenes, or fleshy and indehiscent, a drupe with 4-8 pyrenes.

                                         20 Flower apocarpous; fruit an aggregate of follicles or achenes

                                         20 Flower syncarpous; fruit either a capsule or a fleshy drupe.

                                           21 Ovary 1-carpellate; fruit a 1-seeded drupe

                                           21 Ovary 2-8-carpellate; fruit either a capsule or a drupe with 4-8 pyrenes

                                             22 Ovary 2-8-locular; fruit fleshy and indehiscent, a drupe with 2-8 pyrenes; flowers mostly functionally unisexual (or sometimes bisexual in RHAMNACEAE).

                                               23 Petals connate at the base; stamens alternate to the petals and opposite to the sepals; fruit 4-8-locular, with 4-8 pyrenes

                                               23 Petals separate (or absent in Rhamnus alnifolia); stamens opposite to the petals (when present) and alternate to the sepals; fruit 2-4-locular, with 2-4 pyrenes

                                             22 Ovary 2-3- or 5-locular; fruit dry and dehiscent, a capsule; flowers bisexual (except Stillingia in EUPHORBIACEAE).

                                                 24 Ovary and capsule 5-locular; stamens 10-many.

                                                    25 Stamens 10; corolla urceolate, sympetalous

                                                    25 Stamens many; corolla spreading, apopetalous

                                                 24 Ovary and capsule 2-3-locular; stamens 2, 5, or 10.

                                                      26 Leaves > 5× as long as wide; stamens 2; ovary and capsule 3-locular; [plants of the Coastal Plain of SC, GA, AL, and FL]

                                                      26 Leaves < 3× as long as wide; stamens 5 or 10; ovary and capsule 2-3-locular; [plants collectively widespread].

                                                        27 Stamens 5; ovary and capsule 2-locular; leaves elliptic (widest near the middle), the teeth fine (usually > 5 points per cm of margin), and along much of the margin; inflorescence a terminal raceme; hairs of the lower leaf surface simple, erect

                                                        27 Stamens 10; ovary and capsule 3-locular; leaves obovate (widest towards the apex), the teeth obscure to coarse (usually < 4 points per cm of margin), and primarily in the upper half of the leaf; inflorescence a terminal or axillary raceme or cyme; hairs of the lower leaf surface either simple and appressed, or stellate.

                                                          28 Leaf margins regularly and evenly serrate in the upper half of the leaf (usually nearly entire towards the base); inflorescence an elongate, many flowered (>30) raceme borne at the end of branchlets of the season; corolla of separate petals, the stamens separate; hairs of the lower leaf surface simple and appressed

                                                          28 Leaf margins wavy or irregularly dentate, mainly in the upper half of the leaf; inflorescence a few flowered (<20) axillary raceme, cyme, or cluster; corolla fused basally into a tube, the stamens adnate to the tube; hairs of the lower leaf surface stellate

1 Leaves evergreen.

  2 Petiole flanged or winged, constricted at the base of the blade; fruit a hesperidium

  2 Petiole linear (not flanged or winged with leafy tissue); fruit various. {add to 2b: [Sapium] EUPHORBIACEAE, [Photinia] ROSACEAE, [Prunus (caroliniana)] ROSACEAE, [Ilex (cassine, myrtifolia)] AQUIFOLIACEAE}

    3 Leaves 7-20 cm long, usually at least some on a branch > 12 cm long, thick in texture but readily flexible when fresh.

      4 Inflorescence of a solitary flower, axillary, 5-7 cm across; fruit a capsule, ca. 1 cm in diameter

      4 Incflorescence a corymb of many, smaller flowers; fruit a pome, 0.4-0.8 (-1.2) cm in diameter

    3 Leaves 3-12 cm long, thick in texture and also noticeably stiff.

        5 Leaf with a spinose margin, the marginal spines well-developed, generally arrayed along most of the leaf margin and borne at nearly a right angle to the midvein

        5 Leaf margins serrate with one or a few stiff teeth (sometimes sharpish, but not spines), these usually towards the apex of the leaf and oriented towards the leaf apex

1 Leaves deciduous.

          6 Secondary veins neatly pinnate, the veins on each side of the midrib evenly spaced, parallel to one another, and extending nearly or actually to the leaf margin; fruit either a 1-seeded nut (dry, with or without samaroid wings, bracts, a subtending cupule, or an enclosing and valvate involucre) or a fleshy drupe with 2-4 stones.

             7 Leaves doubly-serrate, the number of teeth greater than the number of the pinnate secondary veins (sometimes obscurely so in Planera in ULMACEAE); fruit a nut or samaroid nut, lacking a cupule or valvate involucre, though sometimes associated with green, leaf-like bracts.

               8 Flowers bisexual, in axillary fascicles, the tree androgynous; leaf base strongly asymmetrical (oblique) or nearly or quite symmetrical.

             7 Leaves singly serrate or crenate, the teeth the same number as the secondary veins; fruit either a fleshy drupe with 2-4 stones, or a nut with a cupule (acorn) or enclosed by a valvate involucre that splits at maturity.

                 9 Fruit a fleshy drupe with 2-4 stones

                 9 Fruit dry, single-seeded (or with 1-4 nuts in Castanea).

                   10 Fruit > 9 mm long or wide, either a nut with a cupule (acorn) or 1-4 nuts enclosed by a valvate involucre that splits at maturity

                   10 Fruit < 9 mm long and wide, leathery, indehiscent, winged or not

          6 Secondary veins not as above, usually arching and/or branching or reticulating well before reaching the leaf margin; fruit various.

                     11 Leaves strongly 3-5-veined from the base; leaf blade cordate or truncate, often oblique.

                       12 Inflorescence terminal, a compound cyme; peduncles and pedicels becoming swollen, fleshy, and juicy at maturity; [plant rarely naturalized]

                       12 Inflorescence axillary, a solitary flower, a fascicle or cluster, or a cyme; peduncles and pedicels remaining stalk-like; [collectively widespread and common].

                          13 Flowers unisexual, plants monoecious; pith of mature twigs chambered with hollow sections between soft partitions

                          13 Flowers bisexual; plants hermaphroditic; pith of mature twigs continuous without hollow sections between partitions.

                            14 Flowers bisexual; inflorescence an axillary cyme; fresh leaves and stems lacking white latex; fruit simple, a 1-seeded nut; main leaf veins splitting several times towards the leaf margin and leading into the teeth without rejoining and forming a marginal vein; basal veins 5, palmate, all joining together at the summit of the petiole; main lateral leaf veins (above the basal veins) often opposite; winter buds with 3 entire bud scales (1 much smaller than the other 2)

                            14 Flowers unisexual, the pistillate inflorescence a head, the staminate inflorescence a catkin, borne on the same tree (monoecious) or on separate trees (dioecious); fresh leaves and stems with white latex; fruit a multiple of fleshy achenes; main leaf veins splitting towards the margin but then rejoining to form a prominent, looping (scalloped) marginal vein; basal veins 3, palmate, sometimes an additional prominent vein on each side joining the lateral vein above its divergence from the petiole end; main lateral leaf veins (above the basal veins) mainly alternate; winter buds with 5 ciliate-margined bud scales

                     11 Leaves pinnately veined; leaf blade base cordate, subcordate, truncate, rounded, or cuneate base, not oblique.

                              15 Inflorescence a terminal raceme of racemes, with more than 50 flowers; petals connate, urceolate; fruit a 5-valved capsule, < 6 mm in diameter; fresh leaves with a sour taste

                              15 Inflorescence various, either with < 30 flowers or if with > 50 flowers a catkin (with a single axis); corolla with separate petals (or petals absent); fruit various, fleshy or dry, if a 5-valved capsule (Franklinia in THEACEAE), then 15-20 mm in diameter; fresh leaves without a sour taste.

                                16 Pubescence stellate (look especially in vein axils on the undersurface of the leaf)

                                16 Pubescence simple (or absent).

                                  17 Flowers very large and showy, 7-9 cm across; fruit a subglobose capsule 1.5-2 cm in diameter

                                  17 Flowers less than 2 cm across; fruit either fleshy and indehiscent, a drupe, samara, or pome, or dry and dehiscent, an ovoid or lanceolate capsule < 0.7 cm in diameter.

                                    18 Flowers unisexual, borne either in axillary catkins; trees dioecious; fruit either dehiscent, a lanceoloid or ovoid capsule (SALICACEAE) or indehiscent, a samara (Eucommia ulmoides).

                                       19 Plants bearing latex; fruit a samara, 25-32 mm long, the apex emarginate

                                       19 Plants not bearing latex; fruit a lanceoloid or ovoid capsule

                                    18 flowers bisexual (unisexual in Ilex in AQUIFOLIACEAE), borne variously in terminal or axillary clusters, cymes, racemes, or umbels, but not at all catkin-like; trees hermaphroditic (dioecious in AQUIFOLIACEAE); fruit indehiscent, a fleshy drupe or pome with 1-many seeds.

                                         20 Pith of twigs with transverse diaphragms and also continuous between the diaphragms (make a longitudinal section of twig and use at least 10× magnification; look for translucent diaphragms spaced at < 1 mm apart, with whiter pith tissue between them); fruit distinctly longer than broad, a 1-seeded drupe

                                         20 Pith of twigs lacking diaphragms, continuous and homogeneous; fruit either suborbicular to spherical or pear-shaped, either a several- to many-seeded pome, or a berry-like drupe with 4-8 seeds, or a 1-seeded drupe.

                                           21 Vascular bundle scars 1 in each leaf scar; fruit a berrylike drupe with 4-8 bony pyrenes; ovary superior, the calyx persistent at the base of the fruit

                                           21 Vascular bundle scars (2-) 3 in each leaf scar; fruit a pome or 1-seeded drupe; ovary either inferior and the calyx persistent at the summit of the fruit (Amelanchier, Crataegus, Malus, Pyrus) or superior and the calyx not at all persistent at the base of the fruit (Prunus)