1 Plants lacking chlorophyll (holoparasitic), with foliage and stems variously pink, purple, brown, tan, orange, or white.

  2 Stem paniculately branched; flowers dimorphic, those low in the inflorescences small, pistillate, and fertile, those high in the inflorescence larger, apparently perfect but functionally staminate; [tribe Orobancheae]

  2 Stem simple (rarely few-branched); flowers all alike.

    3 Calyx deeply cleft on the lower side; stamens exserted; [tribe Rhinantheae]

    3 Calyx either nearly regular, or deeply cleft above and below into 2 lateral halves; stamens included; [tribe Orobancheae].

      4 Flowers solitary on a long pedicel (appearing as a scape, the true stem entirely underground or nearly so)

      4 Flowers several-many, sessile or subsessile in a dense spike.

        5 Calyx 5-lobed, the lobes subequal, all well-developed

        5 Calyx 2-4-lobed, rarely 5-lobed, but then the fifth lobe minute and much smaller than the other lobes.

          6 Calyx divided to the base into 2 lateral halves, these usually 2-lobed, the 4 lobes long-attenuate or caudate; stem unbranched

          6 Calyx tubular, with 4 (-5) lobes about the length of the calyx tube; stem branched (except in depauperate individuals)

1 Plants with chlorophyll (hemiparasitic), with foliage and stems normally green.

             7 Stem leaves alternate.

               8 Leaves pinnately lobed; [tribe Rhinantheae]

               8 Leaves entire or 3-5-lobed at the tip.

                 9 Bracts subtending flowers orange, red, or yellow; calyx 4-lobed; capsule loculicidal; pedicel lacking bracteoles; seeds broad, wingless; [tribe Castillejeae]

                 9 Bracts subtending flowers green; calyx 5-lobed; capsule septicidal and tardily also loculicidal; pedicel with 2 bracteoles; seeds narrow, winged; [tribe Cymbarieae]

             7 Stem leaves (at least the lower) opposite.

                   10 Corolla salverform; [tribe Buchnereae].

                     11 Plant strict, unbranched unless damaged; flowers in a terminal spike; corolla purple; [native, sometimes weedy]

                     11 Plant strongly branched; flowers solitary and axillary; corolla red or orange; [exotic, in agricultural fields]

                   10 Corolla various, but not salverform.

                       12 Calyx 4-lobed or essentially unlobed; corolla strongly bilabiate, the upper lip consisting of 2 petals almost wholly connate and strongly cucullate (hooded); corolla white or yellow; [tribe Rhinantheae].

                          13 Stem leaves pinnately lobed, the lobes rounded and themselves crenate; perennial, 3-8 dm tall

                          13 Stem leaves either toothed with acuminate teeth, or entire (bracteal leaves in and near the inflorescence sometimes pectinately fringed); annual, 1-4 dm tall

                            14 Stem leaves toothed with acuminate teeth; seeds 10-18 per capsule

                            14 Stem leaves entire (bracteal leaves in and near the inflorescence sometimes pectinately fringed); seeds 1-4 per capsule

                       12 Calyx 5-lobed; corolla 5-lobed, the lobes relatively similar in size and shape, spreading; corolla yellow, orange, red, or pink; [tribe Gerardieae].

                              15 Corolla yellow or orange; leaves either lanceolate or broader, at least the basal pinnately or bipinnately lobed or toothed, or pinnately or bipinnately divided into linear segments.

                                16 Leaves pinnately or bipinnately divided into linear segments up to 2 mm wide; corolla rotate, the tube shorter than the lobes

                                16 Leaves not lobed or divided, or the segments broader; corolla tubular, campanulate, or funnelform, the tube much longer than the lobes.

                                  17 Corolla orange, tubular, the tube narrow and straight, > 5× as long as the diameter

                                  17 Corolla yellow, campanulate or funnelform, the tube conical, < 4× as long as the diameter.

                                    18 Anthers pubescent; lower leaves < 12 cm long

                                    18 Anthers glabrous; lower leaves 20-40 cm long

1 Inflorescence an involucrate 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

1 Inflorescence, flower, and fruit structure various, but not with the combination of features as above (sometimes the flowers in a head, e.g. Pycnanthemum in LAMIACEAE, but then with other features differing, such as stamens 4, or green calyx present, or fruit a schizocarp of mericarps, etc.).

  2 Leaves scale-like, stems fleshy; flowers embedded in the fleshy stem, no perianth present; [saline environments (coastal or rarely inland)].

  2 Leaves small to large; stems not fleshy; flowers sessile or on pedicels; [collectively of many habitats, saline and not].

    3 Ovary inferior or partially inferior.

      4 Perianth of a single whorl (petals absent) (note that in Mirabilis in NYCTAGINACEAE the petaloid calyx is subtended by a 5-lobed fused set of involucral bracts).

        5 Leaves herbaceous, suborbicular, about as long as wide or wider than long; calyx 3- or 4-merous; stamens 4, 8, or 12.

          6 Plant ascending, with a single node (2 leaves); leaves > 6 cm long and wide; calyx 3-merous, brown to yellowish; stamens 12

          6 Plant creeping, with many nodes; leaves 3-15 mm long and wide; calyx 4-merous, yellow to greenish; stamens 4 or 8

        5 Leaves fleshy, linear, lanceolate, to broadly ovate, at least slightly longer than broad; calyx 5-merous; stamens 3, 5, or 10.

             7 Flowers axillary, sessile or nearly so, solitary or a few; petaloid sepals widely spreading, separate; leaves linear to oblanceolate; stamens 5 or 30-50

             7 Flowers in terminal cymose panicles; petaloid sepals connate into a narrow tube (reminiscent of the corolla of Ipomoea); leaves lanceolate, elliptic, ovate, or broadly ovate; stamens 3 or 5

      4 Perianth in 2 whorls (sepals and petals both present).

               8 Petals distinct; inflorescence diffuse.

                 9 Leaves distinctly 3-veined from the base, the 3 veins converging again at the leaf apex

                 9 Leaves with prominently pinnate venation

               8 Petals connate into a tube (at least basally); inflorescence often a head or dense terminal cyme (also axillary, or solitary on long peduncles).

                   10 Petals 5; stamens 3, 4, or 5

                     11 Creeping subshrub; flowers paired at tip of an upright peduncle

                     11 Upright herb; flowers in axils or terminal corymbs

                       12 Flowers in terminal corymbs; fruit dry

                       12 Flowers axillary; fruit fleshy

                   10 Petals 4 (or 6 or 8 in Richardia in RUBIACEAE); stamens 4, 6, or 8.

                          13 Inflorescence a head, subtended by 4 large bright white bracts

                          13 Inflorescence a head or more diffuse (see below), sometimes subtended by green bracts.

                            14 Leaves serrate; corolla bilaterally symmetrical (especially the flowers near the outer edge of the head); inflorescence a head

                            14 Leaves entire; corolla radially symmetrical; inflorescence a head or more diffuse (see below).

                              15 Petals acute; flowers in terminal panicles, cymes, or panicles, or axillary; plant habit various, not simultaneously with all the characters below

                              15 Petals broadly rounded; flowers axillary, solitary; plant a diffusely branched herb with linear leaves

    3 Ovary superior.

                                16 Perianth of a single whorl (petals absent) or missing entirely (petals and sepals both absent). {key lead number needs adjusting}

                                  17 Inflorescence a cyathium, consisting of a single pistillate flower (reduced to a single 3-carpellate pistil) and 2 or more staminate flowers (each reduced to 1 stamen), borne in a cup-like involucre, the involucre bearing pointed or rounded glands, these sometimes brightly colored and petaloid, mimicking an individual flower (the cyathia then secondarily arranged in terminal cymes, or solitary and axillary, etc.); fresh plants with milky juice; fruit a 3-lobed, 3-locular capsule

                                  17 Inflorescence not a cyathium (and staminate or bisexual flowers with > 1 stamen, except Callitriche in PLANTAGINACEAE); fresh plants lacking milky juice; fruit various, not as above.

                                    18 Flowers 1 (or 2) in leaf axils; leaves entire.

                                       19 Flowers unisexual; sepals 0; flowers (staminate) with 1 stamen

                                       19 Flowers bisexual; sepals 4; flowers with 2, 4, or 6 stamens.

                                         20 Leaves of an opposite pair markedly different in size

                                         20 Leaves of an opposite pair essentially the same size

                                    18 Flowers many, in axillary spikes, cymes, or glomerules, or in terminal spikes, heads, cymes, or panicles; leaves entire or serrate.

                                           21 Fruit a 2-locular capsule

                                           21 Fruit single-seeded, an achene or utricle.

                                             22 Leaves serrate, regularly and sharply so; plants with stinging hairs (or not)

                                             22 Leaves entire, or with a few very obscure crenations (Iresine) or basally disposed rounded lobe-like teeth (Atriplex); plants without stinging hairs.

                                               23 Leaves of a pair slightly to strongly different in size

                                               23 Leaves of a pair the same size.

                                                 24 Styles 1-2 (-3); leaves 2-30 mm long, 0.5-8 mm wide, linear or narrowly elliptic

                                                 24 Style 1; leaves generally either longer than 30 mm, or wider than 8 mm (if linear and smaller than those dimensions, then fleshy).

                                                    25 Tepals scarious; inflorescence of heads, spikes, or panicles

                                                    25 Tepals herbaceous; inflorescence of glomerules, these axillary or arrayed in spikes or panicles

                                16 Perianth in 2 whorls (sepals and petals both present).

                                                      26 Gynoecium of 4-many pistils, each 1-carpellate.

                                                        27 Pistils 4-5, in a single whorl; stamens 4, 5, 8, or 10; fruit an aggregate of follicles

                                                        27 Pistils many, spiral; stamens many; fruit an aggregate of plumose achenes

                                                      26 Gynoecium either of 1 pistil (with 1 or more carpels), or of 2 pistils, united only by the style and stigma (APOCYNACEAE).

                                                          28 Petals not at all connate, not even at their bases.

                                                            29 Leaves with pellucid punctate glands (most easily visible with transmitted light); stamens often fascicled into 3, 4, or 5 fascicles; petals yellow or pinkish

                                                            29 Leaves lacking pellucid punctate glands; stamens not fascicled; petals variously colored.

                                                              30 Sepals 2; stamens opposite the petals

                                                              30 Sepals 3-7; stamens opposite the sepals.

                                                                 31 Petals 3; sepals 5, dimorphic, the 2 outer sepals narrower than the 3 inner and concave sepals; stamens (3-) 5-15 (-25)

                                                                 31 Petals 4-7; sepals 4-7, normally monomorphic; stamens 4, 5, 6, 8, 10, or 12 (or sometimes rarely 2 or 3).

                                                                   32 Capsule 2-5 (-6) locular; style 1; perianth 4-7-merous; stamens 4, 6, 8, 10, or 12

                                                                   32 Capsule either 1-locular of 10-locular; styles 2-5; perianth 4-5-merous; stamens 4, 5, 8, or 10 (or rarely 2 or 3).

                                                                     33 Capsule 1-locular, dehiscent apically by teeth or valves; sepals connate into a tube or separate; styles 2-5; perianth 4-5-merous; stamens 4, 5, 8, or 10 (or rarely 2 or 3)

                                                                     33 Capsule 10-locular (each of the 5 carpels divided at maturity), septicidal; sepals distinct or nearly so; styles 5, perianth 5-merous; stamens 5

                                                          28 Petals connate at least for a short distance at their bases.

                                                                       34 Corolla radially symmetrical (or so slightly bilaterally symmetrical as to be mistakable as radially symmetrical); stamens as many as the corolla lobes (or 1 less in Ruellia in ACANTHACEAE, Buchnera in OROBANCHACEAE, Trichostema in LAMIACEAE, and Verbena in VERBENACEAE); carpels 2 or 3.

                                                                         35 Pistils 2, united only by the style and stigma; fruit a schizocarp of 2 1-carpellate follicles (often single by abortion); plant with milky juice when fresh (except Catharanthus); leaves entire

                                                                         35 Pistil 1 (of 2-5 fused carpels); fruit either a 2-5-carpellate capsule or of 2 or 4 1-seeded nutlets derived from 2 carpels; plant lacking milky juice; leaves entire or serrate.

                                                                           36 Ovary and capsule 3-5-carpellate; capsule 3- or 1-locular.

                                                                              37 Sepals 2

                                                                              37 Sepals 5.

                                                                                38 Inflorescence a terminal cyme; corolla salverform, with an elongated and very narrow tube, pink or white; capsule 3-locular

                                                                                38 Inflorescence various but not cymose, of terminal or axillary racemes or panicles, or of solitary axillary flowers; corolla connate only at the base, the petals appearing nearly separate (not salverform); capsule 1-locular

                                                                           36 Ovary and capsule 2-carpellate; fruit either a 2-locular capsule or of 2 or 4 1-seeded nutlets derived from 2 carpels.

                                                                                  39 Stamens 4-12, the same number as the corolla lobes; corolla (and the flower as a whole) strictly radially symmetrical.

                                                                                    40 Capsule septicidal; corolla white, pink, blue, yellowish white, or greenish white; inflorescence either a terminal or axillary cyme, or a terminal panicle or raceme, or a terminal or axillary cyme reduced to 1 or a few flowers

                                                                                    40 Capsule loculicidal and also deeply 2-lobed; corolla white, pink, or scarlet with a yellow interior; inflorescence of cymosely arranged spikes

                                                                                  39 Stamens either 4, 1 fewer than the 5 corolla lobes, or 2 (with 2 staminodes); corolla usually slightly bilaterally symmetrical (the flower as a whole made bilaterally symmetrical by the 2 or 4 stamens).

                                                                                      41 Leaves entire; corolla tube flaring for all of its length

                                                                                        42 Fruit a schizocarp of 4 1-seeded nutlets; inflorescence terminal, of cymes; corolla ca. 5 mm long; leaves prominently 3-veined

                                                                                        42 Fruit a capsule; inflorescence axillary, of cymes or clusters (often reduced to a solitary flower); corolla > 12 mm long; leaves with single primary vein

                                                                                      41 Leaves serrate; corolla salverform, the tube narrow and nearly the same diameter for most of its length; inflorescence a terminal spike, raceme, raceme of racemes, or head.

                                                                                           43 Fruit a 2-locular capsule; stamens inserted near the base of the corolla tube

                                                                                           43 Fruit a schizocarp of 4 mericarps; stamens inserted near or above the middle of the corolla tube

                                                                       34 Corolla bilaterally symmetrical (or the corolla 2-lipped but the corolla lobes twisted so as to make the flower asymmetrical); fertile stamens fewer than the corolla lobes (except Plantago in PLANTAGINACEAE, which is equal, with 4 each; a few genera have a 5th, sterile, stamen which is obviously different in form than the 4 fertile stamens) (note that many corollas are bilabiate and the number of corolla lobes, 4 or 5, may be difficult to interpret); carpels 2.

                                                                                             44 Carpels 2, each carpel slightly to deeply lobed, separating at maturity into 4 half-carpellate units (not separating in Phyla in VERBENACEAE); fruit a schizocarp of 4 mericarps (or 2 nutlets in Phyla in VERBENACEAE).

                                                                                               45 Inflorescence a thyrse, verticillaster, or terminal cyme, the flowers borne in cymose lateral branches; corolla strongly bilaterally symmetrical (rarely nearly radially symmetrical); stems square in ×-section (or sometimes rounded, especially on older growth); fresh plants often (but not always) aromatic

                                                                                               45 Inflorescence of spikes, racemes, or heads, the flowers or fruits single at nodes; corolla often nearly radially symmetrical; stems rounded in X-section (rarely square); fresh plants usually not aromatic

                                                                                             44 Carpels 2, unlobed; fruit a capsule (or an achene in Phryma).

                                                                                                 46 Stamens 2.

                                                                                                   47 Corolla 4 lobed, almost radially symmetrical; corolla scarious, white, or bluish

                                                                                                   47 Corolla 4-5-lobed, either strongly bilabiate or salverform (Pseuderanthemum in ACANTHACEAE); white, blue, or yellow.

                                                                                                     48 Inflorescence an axillary cluster or spike

                                                                                                     48 Inflorescence of solitary (rarely 2) axillary flower. {add [Hypoestes] ACANTHACEAE}

                                                                                                        49 Sepals 4

                                                                                                        49 Sepals 5, distinct or nearly so.

                                                                                                          50 Corolla barely bilaterally symmetrical, the lobes about as long as the tube; outer sepals ovate, much wider than the inner sepals

                                                                                                          50 Corolla distinctly bilabiate, the lobes shorter than the tube; sepals of nearly the same width.

                                                                                                            51 Sterile stamens (the lower pair) consisting of slender filaments

                                                                                                            51 Sterile stamens minute or completely absent

                                                                                                 46 Stamens 4.

                                                                                                              52 Corolla 4 lobed, nearly radially symmetrical; corolla scarious

                                                                                                              52 Corolla 5-lobed, distinctly bilabiate or in some nearly radially symmetrical; corolla colored.

                                                                                                                53 Flowers in terminal racemes, panicles, or spikes, the inflorescence not interspersed with large, leaf-like bracts.

                                                                                                                  54 Sepals separate to the base or nearly so, not forming a tube

                                                                                                                  54 Sepals connate for at least 0.3× their length to form a tube (this cup-like and flaring in Scrophularia in SCROPHULARIACEAE).

                                                                                                                     55 Inflorescence a diffuse panicle; corolla 5-11 mm long, reddish-brown (sometimes with some yellow); fruit a septicidal capsule

                                                                                                                     55 Inflorescence of 1 or more terminal (and sometimes upper axillary) spikes or racemes; corolla 10-50 mm long (6-8 mm long in Phryma in PHRYMACEAE), white, pink, blue, purple, or yellow; fruit either a loculicidal capsule (OROBANCHACEAE) or a single seeded achene (Phryma in PHRYMACEAE).

                                                                                                                       56 Corolla 10-50 mm long, pink, blue, purple, or yellow; fruit a loculicidal capsule

                                                                                                                       56 Corolla 6-8 mm long, white to pale pink; fruit a 1-seeded achene contained in the accrescent calyx, this “lopping down” against the inflorescence axis

                                                                                                                53 Flowers axillary and solitary, borne in the axils of normally-sized leaves or somewhat reduced but still large and leaf-like bracts [some taxa keyed here and below].

                                                                                                                         57 Sepals separate to the base or nearly so, not forming a tube.

                                                                                                                           58 Corolla distinctly bilabiate

                                                                                                                           58 Corolla not bilabiate, only slightly bilaterally symmetrical.

                                                                                                                             59 Leaves serrate, 2.0-4.5 cm long; plant usually blackening on drying

                                                                                                                             59 Leaves entire, either mostly larger or smaller [see below]; plant not blackening on drying

                                                                                                                               60 Leaves 0.6-2.8 cm long, round, obovate, or broadly elliptic, < 1.8× as long as wide; plants creeping, ascending to 3 dm tall; [plants of wet places]

                                                                                                                               60 Leaves 3-30 cm long, narrowly elliptic to lanceolate, > 2× as long as wide; plants erect or the stems sprawling; [plants mostly of uplands]

                                                                                                                         57 Sepals connate for at least 0.3× their length to form a tube.

                                                                                                                                  61 Corolla yellow, orange, or red.

                                                                                                                                    62 Calyx lobes longer than the tube, or as long as the tube, corolla 25-50 mm long; plants usually blackening on drying

                                                                                                                                    62 Calyx lobes shorter than the tube; corolla 14-22 mm long; plants not blackening on drying.

                                                                                                                                      63 Corolla red or orange, with a very narrow, cylindrical tube, the lobes then flaring into a limb about 1 cm across; plants blackening on drying; [rare exotic, in crop fields, a noxious hemiparasitic weed under quarantine]

                                                                                                                                      63 Corolla yellow, not narrowly cylindrical, the lower lip arched; plants not blackening on drying; [rare, in seepage wetlands]

                                                                                                                                  61 Corolla white, pale blue, lavender, or pink (sometimes with some yellow).

                                                                                                                                        64 Corolla white, blue, or combinations of blue and white (sometimes with some yellow markings); leaves broader, mostly lanceolate; plants not blackening on drying; corolla strongly bilabiate.

                                                                                                                                          65 Upper lip of the corolla hooded, enfolding the anthers

                                                                                                                                          65 Upper lip of the corolla not hooded and enclosing the anthers; plants not blackening on drying.

                                                                                                                                            66 Corolla blue; lower lip of the corolla arched upwards into the throat; plants perennial from rhizomes or crowns, 3-13 dm tall

                                                                                                                                            66 Corolla bicolored, the upper lip white or very pale blue, the lower lip bright blue; lower lip of the corolla folded downward into a pouch enfolding the anthers; plants annuals, 0.5-4 dm tall