1 Cauline leaves palmately compound.

..2 Cauline leaves essentially sessile, and also palmately cleft to the base, and further lacerately divided into linear or oblanceolate segments

..2 Cauline leaves petiolate, with 3-5, sessile or petiolulate, ovate, elliptic, or obovate leaflets (these serrate and sometimes with additional lobes).

....3 Inflorescence a spherical umbel of many flowers; fruit a drupe with 2-3 seeds; stem leaves 3-5

......4 Leaflets 3 (-5), sessile or subsessile, the petiolules 0-3 mm long; larger leaflets 4-8 cm long, 0.5-2.5 cm wide, averaging about 2.5× as long as wide, the apex obtuse to acute; fruit yellow-green when ripe, longitudinally winged and ribbed in ×-section; petals white (rarely tinged with pink); inflorescence nodding in bud; underground storage organ a spherical tuber

......4 Leaflets (3-) 5, petiolulate, the petiolules (7-) 10-25 mm long; larger leaflets 6-15 cm long, 3.5-7 cm wide, averaging about 1.8× as long as wide, the apex acuminate; fruit bright red when ripe, smoothly elliptical in ×-section; petals light green; inflorescence erect in bud; underground storage organ an +/- elongate root, this vertical or horizontal, and sometimes branched

....3 Inflorescence of single terminal flowers on the 1-several branches; fruit an aggregate of achenes; stem leaves 3

1 Cauline leaves simple.

........5 Inflorescence an involucrate head subtended by phyllaries, heads solitary or many, variously arrayed in secondary inflorescences; fruit a cypsela

........5 Inflorescence various, but not as above; fruit various, not as above (sometimes the flowers tightly grouped, but then with other features differing, such as stamens 4, or green calyx present, or fruit a schizocarp of mericarps, etc.).

..........6 Fruit a 3-lobed, 3-locular capsule; 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

..........6 Fruit various, not as above; inflorescence not a cyathium (and staminate or bisexual flowers almost always with > 1 stamen); fresh plants lacking milky juice.

............ 7 Leaves succulent, the terminal whorls closely juxtaposed; pistils 4-5; fruit an aggregate of follicles

............ 7 Leaves herbaceous, thin in texture, whorls separated; pistil 1, of 2-5 fused carpels; fruit a capsule, achene, or drupe.

............ ..8 Larger whorled leaves on a plant < 10 mm wide [some taxa keyed here and under the second lead].

............ ....9 Inflorescence a cymule, either axillary, or axillary and terminal; ovary inferior.

............ ......10 Leaves markedly variable in shape or size in each whorl; fruit a capsule; petals 5

............ ......10 Leaves similar in size and shape in each whorl; fruit dry or fleshy, indehiscent; petals (3-) 4

............ ....9 Inflorescence a terminal raceme, panicle, spike, cyme, corymb, or umbel; ovary superior.

............ ........11 Corolla bilaterally symmetrical, the petals connate; carpels 2; stamens 4, 6, or 8.

............ ..........12 Stamens 4; corolla blue or almost white

............ ..........12 Stamens 6 or 8; corolla pink or yellow

............ ........11 Corolla radially symmetrical, the petals separate; carpels 2, 3, or 5; stamens 5, 10, or many.

............ ............ 13 Inflorescence an axillary umbel; leaves narrowly linear and more than 10× as long as wide, > 20 mm long and < 2 mm wide; whorls of 3-6 leaves

............ ............ 13 Inflorescence a terminal cyme, raceme, panicle, or umbel; leaves as above, or broader in shape, narrower, or shorter; whorls of 3-16 leaves.

............ ............ ..14 Inflorescence a terminal cyme or umbel; corolla white; carpels 5.

............ ............ ....15 Leaves narrowly linear, 12-16 in each whorl; stamens 5

............ ............ ....15 Leaves ovate or obovate, 3 (-4) in each whorl

............ ............ ..14 Inflorescence a terminal raceme or panicle; corolla reddish, maroon, or yellow.

............ ............ ......16 Corolla reddish or maroon

............ ............ ......16 Corolla yellow

............ ..8 Larger whorled leaves on a plant > 10 mm wide.

............ ............ ........17 Inflorescence a spike; perianth absent; fruit a drupe

............ ............ ........17 Inflorescence various, but not a spike; perianth present; fruit various, but not a drupe.

............ ............ ..........18 Inflorescence of terminal involucrate clusters; perianth of 6 tepals; fruit an achene; stamens 9; [plants of very dry habitats]

............ ............ ..........18 Inflorescence various, but not as above; perianth of 2 whorls (the calyx often obsolete in Galium in RUBIACEAE), 3-, 4-, 5-, 6-, or 7-merous; stamens 2-7; [plants of dry-mesic to very wet habitats].

............ ............ ............ 19 Fruit dry or fleshy, indehiscent; petals (3-) 4; ovary inferior

............ ............ ............ 19 Fruit a capsule or follicle, dehiscent; petals 4-7; ovary superior.

............ ............ ............ ..20 Inflorescence an umbel; fresh plants with milky juice

............ ............ ............ ..20 Inflorescence not an umbel; fresh plants with clear juice.

............ ............ ............ ....21 Corolla pink-purple, 6-merous, the petals separate and borne on the edge of a hypanthium; stamens 8, 10, or 12; [plants of wetlands]

............ ............ ............ ....21 Corolla white, yellow, or greenish, 4-, 5-, or 7-merous, the petals fused at least basally into a tube (falling as a unit), not on a hypanthium; stamens 2, 4, 5, or 7; [plants of mesic habitats].

............ ............ ............ ......22 Stamens 2; corolla bilaterally symmetrical

............ ............ ............ ......22 Stamens 4, 5, or 7; corolla radially symmetrical.

............ ............ ............ ........23 Petals yellowish-white, with prominent green streaks; biennial or monocarpic plant, 10-30 dm tall when fertile; leaves 15-35 cm long

............ ............ ............ ........23 Petals white or yellow; perennial plants, 1-15 dm tall; leaves 1-15 cm long.

............ ............ ............ ..........24 Leaves punctate; stem without swollen nodes

1 Calyx immediately subtended by 1-3 pairs of bracts; [tribe Caryophylleae].

..2 Calyx 20-40-nerved

..2 Calyx 15-nerved

1 Calyx lacking subtending bracts.

....3 Sepals 25-62 mm long; calyx lobes longer than the calyx tube, the lobes as long as or longer than the corolla lobes; [tribe Sileneae]

....3 Sepals (1-) 10-28 (-40) mm long; calyx lobes shorter than the calyx tube, the lobes much shorter than the corolla lobes (except Gypsophila).

......4 Styles 2; fruit valves 4; petals appendaged or not; [tribe Caryophylleae].

........5 Sepals 1-5 mm long, the commissures between the sepals scarious.

..........6 Leaves lanceolate to ovate, (1-) 2-20 (-35) mm wide; plants few-branched, or if diffusely-branched, only in the upper half of the plant's length

..........6 Leaves linear, 0.2-2 (-3) mm wide; plants diffusely branched from near the base upwards

........5 Sepals 7-25 mm long, lacking commissures.

............ 7 Calyx tubular, 20-nerved; petals appendaged; perennial

............ 7 Calyx ovoid, 5-nerved; petals not appendaged; annual

......4 Styles 3-5 (or 0 in staminate plants); fruit valves 3, 4, 5, 6, 8, or 10; petals generally appendaged; [tribe Sileneae]

............ ..8 Plant glabrous; calyx glabrous, narrowly funnelform, dilated above the midpoint; petals pink; stem with glutinous zones on upper internodes

............ ..8 Plant glabrous or pubescent; calyx glabrous or pubescent, either tubular (nearly the same diameter through its length) or broadened below the middle (flask-shaped); petals white or pink (rarely absent); stem lacking glutinous zones (except S. antirrhina).

............ ....9 Styles mostly 5; capsule with 5 or 10 teeth; calyx tubular at anthesis, becoming strongly inflated later in S. dioica and S. latifolia.

............ ......10 Petal limbs deeply divided into 4 linear segments; [or, former Lychnis section Uebelinia]

............ ......10 Petal limbs unlobed, emarginate, or shallowly 2-lobed.

............ ........11 Leaf blades with dense silky white hairiness; flowers bisexual; [or former Lychnis section Agrostemma]