1 Leaves all scale-like, 1-3 (-5) mm long, appressed to the stem.

..2 Plants green or purplish-brown, with chlorophyll (hemimycoheterotrophic); [tribe Gentianeae, subtribe Swertiinae]

..2 Plants white or cream, lacking chlorophyll (holomycoheterotrophic); [tribe Voyrieae]

1 Leaves larger, spreading or ascending.

....3 Stem leaves whorled; plants robust, 1-3 m tall; [tribe Gentianeae, subtribe Swertiinae]

....3 Stem leaves opposite; plants generally < 1 m tall.

......4 Calyx lobes 6-8; corolla bright yellow

......4 Calyx lobes 0 (or interpretable as 2) or 4-5; corolla pink, blue, white.

........5 Calyx lobes 0 (but the flower subtended by 2 leaflike bracts that have sometimes been interpreted as sepals); stem leaves obovate, widest near the rounded tip), 0.5-1.5 cm long, crowded near the tip of the stem, basal rosette never present; [of nutrient-rich, mesic forests]; [tribe Gentianeae, subtribe Swertiinae]

........5 Calyx lobes 4-5; stem leaves lanceolate, ovate, elliptic or narrowly elliptic (widest near the middle or toward the base, the tip acute or acuminate), mostly > 1.5 cm long, distributed fairly evenly along the stem, basal rosettes sometimes present; [of various more-or-less open habitats (except some species of Gentiana, which can occur in nutrient-rich, mesic forests)].

..........6 Corolla lobes 5-14, longer than the corolla tube, pink or white; [common natives]; [tribe Chironieae, subtribe Chironiinae].

............ 7 Stigmas shorter than the style

............ 7 Stigmas equaling or longer than the style

..........6 Corolla lobes 4-5, shorter than the corolla tube, blue, lavender, pink or white.

............ ..8 Corolla tube < 2 mm wide; [rare to uncommon exotics, naturalized in disturbed areas]; [tribe Chironieae, subtribe Chironiinae].

............ ....9 Style slightly bifid; stigma lobes reniform to shoe-shaped, fleshy; capsule linear

............ ....9 Style not divided or subcapitate; stigma lobes rhombic to fan-shaped, not fleshy; capsule elliptic to ovoid

............ ..8 Corolla tube > 3 mm wide.

............ ......10 Corolla lobes alternating with corolla appendages (appearing as plaits or lobes, these often toothed, notched, or lacerate, sometimes as long as or longer than the true corolla lobes); main stem leaves cuneate at the base; perennial; [tribe Gentianeae, subtribe Gentianinae]

............ ......10 Corolla lobes not alternating with corolla appendages; main stem leaves rounded to cordate at the base; biennial or annual; [tribe Gentianeae, subtribe Swertiinae].

............ ........11 Corolla lobes 4, finely fringed; main stem leaves rounded at base, with lateral veins obscure; biennial

............ ........11 Corolla lobes 5, entire, not fringed; main stem leaves cordate (the cordate bases often overlapping the opposite leaf), with 2-3 well-developed lateral veins (prominently visible on the lower surface); annual