1 Leaves evergreen.

  2 Petiole flanged or winged (except C. reticulata, which sometimes lacks wings entirely), constricted at the base of the blade; fruit a hesperidium

  2 Petiole linear (not flanged or winged with leafy tissue); fruit various.

    3 Inflorescence a thin (superficially spike-like) thyrse; leaves linear-lanceolate, the petiole apex bearing 2 glands; seeds with a red aril; [waif, Escambia County, FL]

    3 Inflorescence various, not a thyrse (if thin, then flowers arranged in catkins in FAGACEAE); leaves variously lanceolate, elliptic to ovate or rounded, the petiole apex not bearing 2 glands; seeds not bearing red arils; [widespread natives and non-natives]

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

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

        5 Incflorescence a corymb or cyme of many, smaller flowers; fruit a pome, 0.4-0.8 (-1.2) cm in diameter (Photinia) or a drupe of similar size (Ehretia).

          6 Fruit an orange to yellow drupe, ultimately containing 4 seeds (from 2 paired nutlets); inflorescence a cyme

          6 Fruit a pome; inflorescence a corymb

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

             7 Leaves somewhat 2-ranked (subdistichous), the bases of the blades usually oblique; flowers yellowish-green, occasionally present on the trunks (plants cauliflorous), the trunks smooth and white, sometimes fluted (with irregular vertical ridges, at least on larger plants); [c. and s. FL only in our flora area]

             7 Leaves subdistichous or not, the bases of the blades not oblique; flowers variously colored (usually white in Ilex and Ehretia, brownish-white and apetalous in Fagaceae); plants never cauliflorous, the trunks smooth or with thickened ridges, rarely fluted.

               8 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; flowers not catkins, bearing petals; fruit berrylike, usually at least somewhat fleshy

               8 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 somewhat ascendant; flowers catkins and apetalous (FAGACEAE) or bearing petals (Ehretia in EHRETIACEAE); fruit an acorn (not fleshy) or a drupe (somewhat fleshy).

                 9 Flowers bearing petals, arranged in cymes; fruit a drupe, usually at least somewhat fleshy

1 Leaves deciduous.

                   10 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.

                     11 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.

                       12 Flowers unisexual, in catkins, the tree monoecious; leaf base symmetrical

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

                     11 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.

                          13 Fruit a fleshy drupe with 2-4 stones

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

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

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

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

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

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

                                  17 Flowers unisexual, plants monoecious; bark on mature trees usually warty or with corky fissures; pith of mature twigs chambered with hollow sections between soft partitions (Celtis) or solid (Trema).

                                    18 Leaf blades entire or irregularly serrate (the margins usually with at least some portions entire, even if minimal), the lower surfaces glabrous or nearly so; cymes few-flowered (at least pistillate); [collectively widespread]

                                    18 Leaf blade margins uniformly serrate or crenate throughout (the teeth uniform and without some portions entire), the lower surfaces pubescent; flowers many (12-20), arranged in dense axillary cymes; [FL and s. TX only in our area]

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

                                       19 Flowers white, showy, and often singular (the petals 12-20 mm long); fruit a red berry 10-15 mm in diameter; [uncommon non-native, s. FL]

                                       19 Flowers either smaller yellowish-white cymes (Tilia) or unisexual pistillate heads or staminate catkins (Moraceae); fruit either nutlike and bearing a curved bract (Tilia) or a fleshy syncarp (Moraceae); [widespread native and non-natives]

                                         20 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)

                                         20 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

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

                                           21 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

                                           21 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.

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

                                             22 Pubescence simple (or absent).

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

                                               23 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.

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

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

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

                                                 24 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.

                                                      26 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

                                                      26 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.

                                                        27 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

                                                        27 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)