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Keyed in multiple places:

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Key to Linderniaceae

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1 Calyx conspicuously 5-winged (each calyx segment strongly keel-winged)
1 Calyx not winged.
  2 Flowers < 2 mm long.
    3 Leaves elliptic, cuneate at the base; calyx lobes even, all of the sinuses reaching nearly to the base of the calyx
    3 Leaves orbicular, rounded at the base; calyx lobes uneven, 3 of the sinuses extending about halfway to the base of the calyx, the lowermost sinus extending to the base
  2 Flowers > 4 mm long.
      4 Fertile stamens 4; calyx lobes connate at anthesis for > ½ their length, later separating
      4 Fertile stamens 2 (with 2 staminodia without anthers, or with rudimentary anthers); calyx lobes separate, or connate at base for < ¼ the length of the calyx.
        5 Capsule lanceoloid, > 8× as long as its diameter; calyx lobes connate at the base ca. ¼ the length of the calyx
        5 Capsule ovoid to ellipsoid, < 5× as long as its diameter; calyx lobes connate at the base ca. 1/8 the length of the calyx

Key N2: herbaceous dicots with mainly basal, simple leaves

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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 subtended by bracts, e.g. Eryngium in APIACEAE, but then with other features differing, such as stamens 4, or green calyx present, or petals separate, or fruit a schizocarp of mericarps, etc.).
  2 Basal leaves 2-lobed, pinnately lobed, or palmately lobed (not considering cordate, hastate, or auriculate leaf bases as “lobed”).
    3 Basal leaves 2-lobed, hinged between the lobes, each lobe with stiff, marginal, eyelash-like bristles; [Coastal Plain of NC and SC, rarely planted and weakly naturalized elsewhere]
    3 Basal leaves 3-many-lobed, palmately or pinnately; [collectively widespread].
      4 Leaf lobing pinnate.
        5 Gynoecium of separate pistils (each with a single carpel); fruit an aggregate
        5 Gynoecium of a single pistil (with 2, rarely more, carpels); fruit simple.
          6 Stamens many; sepals 2, petals 4; fresh plants with yellow, orange, or white milky juice
          6 Stamens 4, 5, or 6; sepals 4 or 5; petals 4 or 5.
             7 Petals 4, distinct; stamens 6
             7 Petals 5, fused; stamens 2, 4, or 5.
               8 Corolla radially symmetrical; stamens 5
               8 Corolla 2-lipped, bilaterally symmetrical or asymmetrical; stamens 2 or 4.
                 9 Corolla lobes not twisted, the flower bilaterally symmetrical; stamens 2
                 9 Corolla lobes twisted so as to make the flower asymmetrical; stamens 4
      4 Leaf lobing palmate.
                   10 Petiole attachment peltate.
                     11 Leaves < 10 cm in diameter
                     11 Leaves > 15 cm in diameter
                   10 Petiole attachment marginal.
                       12 Ovary inferior.
                          13 Petals 4; stamens 8; fruit a capsule
                          13 Petals 5; stamens 5; fruit a schizocarp of 2 mericarps.
                            14 Fruit tuberculate; leaves 3-lobed
                            14 Fruit smooth; leaves with 5 or more lobes
                       12 Ovary superior, or half-inferior by fusion of a hypanthium a part of the way up the ovary wall.
                              15 Gynoecium of separate pistils (each with a single carpel); fruit an aggregate.
                                16 Perianth of 5 green sepals and 5 colored petals.
                                  17 Carpels partly fused, arrayed in a ring of 10-20
                                  17 Carpels separate, spiral, many
                                16 Perianth of a single whorl of 3-12 petaloid sepals (the petals absent or small and rudimentary).
                                    18 Leaves 2, the single flower terminal and associated with the upper leaf; fruit an aggregate of berries
                                    18 Leaves normally > 2, flowers not as above; fruit an aggregate of achenes, utricles, or follicles
                              15 Gynoecium of a single pistil (with 1-5 carpels); fruit simple.
                                       19 Hypanthium present, partially fused or not fused to the pistil; ovary partially inferior to superior
                                       19 Hypanthium absent; ovary superior.
                                         20 Petals connate at base; leaves sharply toothed
                                         20 Petals distinct; leaves with rounded lobes or teeth.
                                           21 Corolla radially symmetrical; petals 8-12; capsule fusiform, narrowed to both ends, > 5× as long as wide
                                           21 Corolla bilaterally symmetrical; petals 5; capsule ovoid, < 2× as long as wide
  2 Basal leaves not lobed, at most serrate or crenate (and sometimes also cordate, hastate, auriculate, or peltate at the base).
                                             22 Basal leaves petiolate, the blade with a cordate, hastate, auriculate, or peltate base.
                                               23 Leaf margins entire.
                                                 24 Inflorescence a terminal and/or axillary raceme, panicle, or cyme of many small flowers; fruit an achene; perianth uniseriate, of 0, 4-5, or 6 tepals.
                                                    25 Flowers unisexual; staminate flowers 4-5 tepals, pistillate flowers lacking a perianth
                                                    25 Flowers bisexual; flowers with 6 tepals
                                                 24 Inflorescence either a terminal spike, or a 1-7-flowered terminal cyme, or of a solitary axillary or terminal flower; fruit various; perianth biseriate (of differentiated sepals and petals (except uniseriate, of 3 fused sepals in ARISTOLOCHIACEAE).
                                                      26 Flowers bilaterally symmetrical; inflorescence a terminal spike (with > 20 flowers); petals 4, usually scarious, transparent; sepals 4, green; stamens 4
                                                      26 Flowers radially symmetrical; inflorescence either of a solitary flower or of a 1-7-flowered terminal cyme; petals 5, 8-12, or 0; sepals 5 (green), 3 (brown), or 5-9 (yellow); stamens 5, 12, or many.
                                                        27 Gynoecium of separate pistils (each with a single carpel); fruit an aggregate of achenes or follicles; flowers bright yellow, either of 5-9 distinct petaloid sepals, or of 8-12 distinct petals subtended by 3-4 green distinct sepals
                                                        27 Gynoecium either of a single pistil with 6 carpels or of a single pistil with 4 carpels or of 2 nearly separate carpels; fruit a simple capsule (or deeply 2-lobed); flowers white, brown, or greenish, either of 5 fused or distinct white petals and 5 fused or distinct green sepals, or of 3 fused brown or greenish petaloid sepals.
                                                          28 Flowers brown or green, of 3 fused brown or greenish petaloid sepals (and 0 petals); carpels 6; stamens 12; leaves 4-10 cm wide
                                                          28 Flowers white, of 5 white or whitish petals and 5 green sepals; carpels 2; stamens 5; leaves 1-12 (-15) cm wide
                                                            29 Petals separate; sepals separate; plant glabrous
                                                            29 Petals fused; sepals fused; carpels 2; plant pubescent.
                                                              30 {XXXX}; [common, widespread in our area]
                                                              30 {YYYY}; [rare exotic]
                                               23 Leaf margins crenate, serrate, or incised.
                                                                 31 Gynoecium of separate pistils (each with a single carpel); fruit an aggregate; perianth of 5 green sepals and 5 colored petals.
                                                                   32 Carpels 10-20, partly fused, arrayed in a ring; petals white, pink, red, or purplish
                                                                   32 Carpels many, separate, spiral; petals yellow or white.
                                                                     33 Flowers lacking a hypanthium; fruit an aggregate of achenes or aggregate of follicles
                                                                     33 Flowers with a hypanthium; fruit an aggregate of drupelets or aggregate of achenes
                                                                 31 Gynoecium of a single pistil (with 1-5 carpels); fruit simple.
                                                                       34 Flowers bilaterally symmetrical; inflorescence of a solitary flower; fruit a 3-locular capsule
                                                                       34 Flowers radially symmetrical; inflorescence an umbel (or composite of umbelliform units, or a terminal panicle.
                                                                         35 Ovary superior; inflorescence a terminal panicle or terminal raceme.
                                                                           36 Inflorescence a terminal raceme; perianth of 4 green sepals and 4 white petals; fruit a silique/silicle; fresh foliage in spring and summer with a strong garlic odor; larger leaves < 10 cm in diameter
                                                                           36 Inflorescence a terminal panicle; perianth of 6 cream-colored petaloid sepals; fruit a winged achene; fresh foliage lacking a garlic odor; larger leaves typically > 30 cm in diameter
                                                                         35 Ovary inferior; inflorescence an umbel (or a composite of umbellate units); fruit a schizocarp of mericarps.
                                                                              37 Petiole attachment peltate
                                                                              37 Petiole attachment marginal (the blade cleft to the petiole.
                                                                                38 Leaf blades longer than wide, sharply V-cleft at the base and otherwise shallowly denticulate
                                                                                38 Leaf blades as broad or broader than long, cleft at the base and also irregularly serrate or crenate around the margin
                                             22 Basal leaves petiolate or not, with a truncate, rounded, or cuneate leaf base.
                                                                                  39 Leaves tubular, with a sutured ventral flange, erect or reclining, adapted as a pitfall for insects (flat, phyllodial leaves sometimes present as well, common in the winter in some species, such as S. oreophila)
                                                                                  39 Leaves flat, not sutured into a tubular shape.
                                                                                    40 Stem leaves opposite; perianth 5-merous, at least the corolla bilaterally symmetrical (barely so in VALERIANACEAE), or the parts curved so as to be asymmetrical (Pedicularis in OROBANCHACEAE); stamens 2, 3, or 4.
                                                                                      41 Ovary inferior; stamens 3
                                                                                      41 Ovary superior; stamens 2 or 4.
                                                                                        42 Corolla narrowly tubular, the five lobes flaring at nearly 90 degrees and nearly radially symmetrical
                                                                                        42 Corolla distinctly 2-lipped (with prominently large upper and lower corolla lobes) or hooded (the upper lip hood-like), distinctly bilaterally symmetrical, or the lobes twisted so as to make the corolla asymmetrical.
                                                                                           43 Corolla yellow, the upper lip often slightly to strongly maroon, hooded but the corolla lobes twisted so as to make the flower asymmetrical
                                                                                           43 Corolla white, lavender, or blue, 2-lipped and bilaterally symmetrical.
                                                                                             44 Sepals connate for at least 0.3× their length to form a tube
                                                                                    40 Stem leaves alternate; perianth radially symmetrical (less commonly bilaterally symmetrical); stamens 5, 6-8, 9, 10 (rarely 4).
                                                                                               45 Ovary inferior (or half-inferior in Samolus).
                                                                                                 46 Perianth 4-merous; stamens 8
                                                                                                 46 Perianth 5-merous; stamens 5.
                                                                                                   47 Inflorescence an umbel; fruit a schizocarp of 2 mericarps
                                                                                                   47 Inflorescence an axillary or terminal raceme; fruit a capsule
                                                                                               45 Ovary superior.
                                                                                                     48 Pistils many, each with a single carpel; fruit an aggregate of achenes
                                                                                                     48 Pistil 1, with 1-5 carpels; fruit simple (a legume, silique/silicle, capsule, utricle, or schizocarp of 4 nutlets).
                                                                                                        49 Corolla bilaterally symmetrical (barely so in Limosella in SCROPHULARIACEAE); stamens 2, 4, 6, 8, or 10.
                                                                                                          50 Stamens 6-8 or 10.
                                                                                                            51 Petals separate; stamens 10
                                                                                                            51 Petals fused; stamens 10 or 6-8.
                                                                                                              52 Stamens 10, monadelphous
                                                                                                              52 Stamens 6-8, epipetalous
                                                                                                          50 Stamens 2 or 4.
                                                                                                                53 Stamens 2
                                                                                                                53 Stamens 4.
                                                                                                                  54 [plants of coastal wetlands]
                                                                                                                  54 [plants of uplands or inland seeps or fens]
                                                                                                                     55 Flowers (and subtending bracts) red or yellow
                                                                                                                     55 Flowers purple, blue, or lavender
                                                                                                        49 Corolla radially symmetrical; stamens 5, 10, 4-6, or 9.
                                                                                                                       56 Perianth of 6 tepals; stamens 4-6 or 9; carpels 3
                                                                                                                       56 Perianth of green sepals and more brightly colored petals; stamens 5 or 10; carpels 2, 3, 4, or 5.
                                                                                                                         57 Leaves covered with sticky, gland-tipped hairs (often red), as flypaper traps for insects
                                                                                                                         57 Leaves lacking sticky gland-tipped hairs.
                                                                                                                           58 Fruit a schizocarp of 4 nutlets (ovary obviously 4-lobed in flower)
                                                                                                                           58 Fruit a capsule or silique/silicle (or utricle in Limonium in PLUMBAGINACEAE).
                                                                                                                             59 Inflorescence of a solitary, terminal flower; carpels 2-3 (-4).
                                                                                                                               60 Corolla with a long tube and flaring corolla lobes (united > ½ its length)
                                                                                                                               60 Corolla of separate petals or united only for a short length (< ¼ its length).
                                                                                                                                  61 Leaves serrate
                                                                                                                                  61 Leaves entire
                                                                                                                             59 Inflorescence of several to many flowers; carpels 5 (3 in Galax in DIAPENSIACEAE).
                                                                                                                                    62 Inflorescence an umbel; petals recurved, pink to almost white
                                                                                                                                    62 Inflorescence a raceme or panicle.
                                                                                                                                      63 Fruit a silique/silicle; petals 4; stamens 6
                                                                                                                                      63 Fruit either a capsule or a utricle; petals 5; stamens 5 or 10.
                                                                                                                                        64 Inflorescence a somewhat to very diffuse panicle, with 3 or more orders of branching, not giving at all the impression that the overall inflorescence is made of racemose units.
                                                                                                                                          65 Leaves entire; stamens 5; [plants of tidal marshes]
                                                                                                                                          65 Leaves serrate or crenate; stamens 10; [plants of various habitats, especially rock outcrops and bottomland forests and streambanks, never in tidal marshes]
                                                                                                                                        64 Inflorescence either a single terminal raceme (sometimes spike-like), or of 1 to several terminal and axillary racemes (these sometimes combined into a diffuse panicle, but one whose structure is clearly made up of many racemes).
                                                                                                                                            66 Inflorescence of 1-several terminal and axillary racemes, the plant typically well-branched, especially from the base; stamens 5
                                                                                                                                            66 Inflorescence of a single, terminal raceme, the plant unbranched; stamens 10 (or 5, with 5 staminodes)
                                                                                                                                               67 Inflorescence spike-like, the flowers many (> 40), barely pedicelled; capsule 3-locular
                                                                                                                                               67 Inflorescence a raceme, the flowers fewer (< 20) and distinctly pedicelled; capsule 5-locular

Key S1: herbaceous dicots with opposite, simple, and unlobed leaves on the stem

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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 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 pink (sometimes almost white), often lined with yellow inside; leaves narrowly linear, often filiform (except lanceolate in A. auriculata); plants usually blackening on drying (some species do not); corolla not strongly bilabiate
                                                                                                                                        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
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