1 Petals blue, red, or pink (rarely white); capsule 5-10 mm long; [section Linum].

  2 Petals red or pink

  2 Petals blue (rarely white).

    3 Inner sepals with minutely ciliate margins; stigmas slender, elongate; capsule 6-10 mm long

    3 Inner sepals entire; stigmas capitate; capsule 5-7 mm long.

      4 Flowers heterostylous (some flowers with stigmas below the anthers, others with stigmas well above the anthers)

      4 Flowers homostylous (flowers with stigmas at about the level to slightly above the anthers)

        5 Perennials; styles 2-12 mm; capsule apices acute

        5 Annuals; styles 1-3 mm; capsule apices obtuse

1 Petals predominantly light to dark yellow (sometimes also with other coloration, including orange, copper, salmon, brown, and red bands or blotches); capsules 1-4 mm long; [section Linopsis].

          6 Outer sepals entire (very rarely sparsely glandular-toothed), the inner sepals entire or sparsely to conspicuously glandular-toothed; leaves without red or brown stipular glands flanking the attachment to the stem.

             7 Fruit as long as broad or longer, its apex acute, apiculate, or obtuse, (2-) 2.2-3.2 (-3.3) mm long; leaves mostly 1.3-4.3 mm wide.

               8 Leaves opposite; fruit subspherical, abruptly short-pointed

               8 Leaves all or mostly alternate (a few pairs of leaves at the base of the stem sometimes opposite); fruit ovoid to pyriform.

                 9 Leaves (1.2-) 2.3-4.3 (-5.6) mm wide, mostly 25-50 below the inflorescence; septa of the fruit sparsely but conspicuously ciliate; false septa incomplete; fruit apex acute, the exposed portions purple

                 9 Leaves (1.0-) 1.3-2.0 (-3.2) mm wide, mostly 50-165 below the inflorescence; septa of the fruit glabrous; false septa virtually complete; fruit apex rounded to apiculate, the exposed portions purple or yellow.

                   10 Fruit 3.4-3.8 mm long, 3.2-3.4 mm in diameter

                   10 Fruit (2.0-) 2.3-3.2 (-3.3) mm long, 1.7-3.1 mm in diameter.

                     11 Fruit ovoid, (2.8-) 3.0-3.2 (-3.3) mm long, 2.5-3.1 mm in diameter, the apex minutely apiculate, the exposed portions yellow; seeds 2.1-2.4 mm long; anthers averaging 1.2 mm long

                     11 Fruit pyriform, (2.0-) 2.3-2.8 (-3.0) mm long, 1.7-2.6 mm in diameter, the apex rounded, the exposed portions purple; seeds (1.6-) 1.7-2.0 (2.1) mm long; anthers averaging 0.8 mm long

             7 Fruit broader than long, its apex depressed, flattened, or broadly rounded, (1.3-) 1.5-2.1 (-2.3) mm long; leaves mostly 1.9-9.3 mm wide.

                       12 Margins of the inner sepals with conspicuous stalked glands (these few or even absent in L. medium); mature fruits of dried specimens usually adhering to the plant.

                          13 Inner sepals conspicuously glandular-toothed; leaf apices minutely apiculate (and translucent); leaves relatively translucent, [widespread in our region]

                          13 Inner sepals sparsely glandular-toothed (or entire); leaf apices obtuse, opaque; leaf blade relatively opaque; [questionably present in n. PA northwards]

                       12 Margins of the inner sepals glandless, or with a few inconspicuous, sessile glands; mature fruits of dried specimens usually shattering and falling freely.

                            14 Styles distinct (free); [collectively widespread in our region].

                              15 Inflorescence paniculate, the lower inflorescence branches not elongate, their tips not nearly reaching the tips of the upper inflorescence branches; branchlets striate-ridged; leaves mostly opposite (usually to beyond the midpoint from the base of the plant to the first inflorescence branch)

                              15 Inflorescence corymbose, some (at least) of the lower branches of the inflorescence elongate, their tips nearly equaling the tips of the upper inflorescence branches; branchlets terete or nearly so; leaves mostly alternate (usually the opposite leaves of the lower stem not extending beyond the midpoint from the base of the plant to the first inflorescence branch)

                            14 Styles connate (united basally); [west of the Mississippi River, in LA, OK, and TX].

                                16 Distal leaves and bracts not ciliate; capsule false septa entirely hyaline, or with cartilaginous portion very narrow, uniform, distal

                                16 Distal leaves and bracts sparsely ciliate; capsule false septa with cartilaginous portion conspicuously broader near base

          6 Inner and outer sepals all very conspicuously glandular-toothed; leaves with 2 red or brown stipular glands flanking the attachment to the stem (these absent or obscure in L. smallii and L. rigidum var. rigidum – but check leaves on the upper and lower stem).

                                  17 Styles distinct (free).

                                    18 Styles 2-3 mm long; petals 4-6.5 mm long; [s. FL]

                                    18 Styles 3-6.5 mm long; petals 7-11 mm long; [TX]

                                  17 Styles connate (united) basally or through most of their length.

                                       19 Capsules dehiscing into 10, 1-seeded segments; sepals persistent.

                                         20 Sepals 2.3-3.5 mm long, acute; inflorescence consisting of 1 or more elongate and racemiform branches; dried plants dark, purple-dotted; [Coastal Plain of FL Panhandle]

                                         20 Sepals (3.1-) 3.6-5 (-7.3) mm long, acuminate; inflorescence an open panicle; dried plants pale green; [widespread, mainly inland provinces except westwards]

                                       19 Capsules dehiscing into 5, 2-seeded segments; sepals persistent or not.

                                           21 Outer sepals ovate or obovate, margins undulate or crenate, with sessile gland near summit of each crenation

                                           21 Outer sepals linear, linear-lanceolate, lanceolate, or narrowly ovate, margins glandular-toothed.

                                             22 Styles 6-9.5 mm long.

                                               23 Petals with prominent wine-colored band below their midpoints

                                               23 Petals reddish below middle.

                                                 24 Sepals green; stigmas green; capsules relatively thick-walled and opaques

                                                 24 Sepals grayish or purplish; stigmas dark gray; capsules relatively thin-walled and translucent

                                             22 Styles 2-6 mm long.

                                                    25 Sepals short-awned; [peninsular FL].

                                                      26 Stem glabrous (or sometimes sparsely puberulent or scabrous near the base); plants (17-) 28-45 (-64) cm tall; petals 11.5-17 mm long; styles 5.1-9.1 mm long; stipular glands usually absent or essentially so

                                                    25 Sepals acute to acuminate; [OK,TX]

                                                        27 Stamens 4-5 mm long

                                                        27 Stamens 6-8 mm long