1 Corolla lobes fimbriate; ovules 2 to each of the 2 placentae (or 4 in P. gilioides); seeds 4 (or 6-8 in P. gilioides) per capsule.

..2 Corolla lobes conspicuously pilose on the back; ovules 4 per placenta (carpel); seeds (6-) 8 per capsule

..2 Corolla lobes glabrous or glabrescent on the back; ovules 2 per placenta (carpel); seeds 4 per capsule.

....3 Corolla white (rarely slightly lavender); pubescence of the stem spreading; lobes of cauline leaves mostly obtuse; seeds 3.0-3.5 mm long

....3 Corolla lavender to blue; pubescence of the stem appressed; lobes of cauline leaves mostly acute; seeds 1.5-3.0 mm long

......4 Ovary below the apex pubescent; outer (lower) surface of corolla lobes usually pubescent; pedicels often short (< 12 mm long)

......4 Ovary below the apex glabrous; outer (lower) surface of the corolla lobes glabrous (or rarely with a very few hairs); pedicels usually > 8 mm long

1 Corolla lobes entire; seeds 4-15 per capsule.

........5 Stamens 1.5-2 mm long; style 1.5-2 mm long; corolla tubular; seeds globose-ovoid, nearly spherical, 4 per capsule.

..........6 Pubescence of the middle stem (from 2nd to 5th node from the base) consisting of appressed to ascending, stiff, pointed hairs, sometimes also with a few gland-tipped hairs < 2 mm long; terminal leaflet of leaves directly subtending an inflorescence with acute to cuneate bases; flowers medium blue; [of rivers in the Atlantic drainage, also west of the Appalachians in rivers of the Mississippi drainage]

..........6 Pubescence of the middle stem spreading or even retrorse, most of the hairs weak and twisted, and many of them glandular-tipped and > 2 mm long; terminal leaflet of leaves directly subtending an inflorescence with obtuse to rounded or truncate bases; flowers light blue; [of rivers in the Mississippi drainage]

........5 Stamens 3-10 mm long; style 3-15 mm long; corolla rotate to broadly campanulate; seeds ovoid-angled, 4-15 per capsule.

............ 7 Corolla 10-15 mm across, blue; plant 10-60 cm tall; seeds 2.5-4 mm long, black; ultimate segments of the leaf 15-45 mm long, 10-25 mm wide; pedicels recurved in fruit; branches of the inflorescence glandular-pubescent

............ 7 Corolla 5-11 mm across, white to blue; plant 5-40 cm tall; seeds 1.5-2.2 mm long, brown; ultimate segments of the leaf 5-15 mm long, 5-9 mm wide; pedicels ascending to spreading in fruit; inflorescence branches variously pubescent, but not glandular.

............ ..8 Basal leaves shallowly toothed or lobed; fruiting pedicels strictly erect, usually shorter than the fruiting calyx

............ ..8 Basal leaves pinnate or deeply pinnatifid; fruiting pedicels ascending or divergent, usually as long as or longer than the fruiting calyx.

............ ....9 Pubescence of the stems, peduncles, and pedicels spreading; calyx lobes spreading at anthesis

............ ....9 Pubescence of the stems, peduncles, and pedicels appressed; calyx lobes ascending or erect at anthesis.

............ ......10 Sepals 4-8 mm long, linear or oblanceolate; marginal bristles of sepals spreading, 1.0-1.5 mm long; plants mostly erect

............ ......10 Sepals 2-4 mm long, narrowly ovate; marginal bristles of sepals appressed, 0.3-1.0 mm long; plants mostly decumbent, branched from the base.

............ ........11 Upper rosette/lowest cauline leaves usually less dissected (< 6 leaflets) and rarely with additional lobing, and a wider terminal leaflet 4-10 mm × 3-7 mm; cauline leaves (third below inflorescence) with 1-4 leaflets, rarely with additional lobes; corolla larger, lobes usually > 4 mm × > 3 mm.

............ ..........12 Corolla more dish-shaped; that is, shallowly concave (best viewed on live specimens), lobes > 4.5 mm wide; upper rosette/lowest cauline leaves usually with < 4 leaflets + lobes, terminal leaflet wider than other leaflets; [calcareous glades and surrounding areas of the Nashville Basin]

............ ..........12 Corolla bowl-shaped or more deeply concave, lobes usually < 5.5 mm wide; upper rosette/lowest cauline leaves usually with > 4 leaflets + lobes; terminal leaflet equal to or wider than other leaflets; [east of the Cumberland Plateau].

............ ............ 13 Upper rosette/lowest cauline leaves usually with 2–6 leaflets sometimes with a few additional lobes, terminal leaflet smaller (approximately 5.5 mm × 4.0 mm); terminal leaflet of cauline leaf (third below inflorescence) usually smaller (approximately 5.0 mm × 2.5 mm); corolla lobes 3.5–5.2 mm × 3.0–4.8 mm; granite outcrops and peripheral areas including roadsides; [Piedmont of SC (and adjacent NC?) and Allendale and Bamberg counties, SC]

............ ............ 13 Upper rosette/lowest cauline leaves usually with 0–4 leaflets, very rarely with additional lobes, terminal leaflet larger (approximately 7.0 mm × 5.0 mm); terminal leaflet of cauline leaf (third below inflorescence) usually larger (approximately 7.0 mm × 3.5 mm); corolla lobes > 4.5 mm long and > 4.0 mm wide; rocky woods, floodplain forests, shale barrens, and ruderal areas including roadsides and railroad embankments; [Mountains, Piedmont, Coastal Plain; PA and south, in the uplands to n. GA, and Coastal Plain to Charleston Co., SC]

............ ............ ..14 Sepals (in flower) 2.6-4.0 mm long; petals 4-6 mm long; marginal bristles of sepals 0.6-0.9 mm long; basal leaves with 1-3 pairs of lateral leaflets, the terminal leaflet larger and usually 3-lobed; cauline leaves with 1-3 pairs of rather broad lobes; [of various habitats (including granitic flatrocks and domes].