1 Styles 3' capsule opening by 6 valves.

  2 Leaves narrow, usually linear, lanceolate, oblanceolate, or narrowly elliptic, the blade 3-10× as long as wide, 0.8-10 mm wide; stems prominently 4-angled.

    3 Sepals 2.0-3.5 mm long; petals 0-3.0 mm long, shorter than the sepals or absent; seeds 0.3-0.9 mm long.

      4 Inflorescence a leafy (or with obvious bracts) terminal cyme of (1-) 5-50 flowers; seeds 0.7-0.9 mm long, smooth or slightly rugose.

        5 Bracts subtending the pedicels green, herbaceous throughout; [Larbreae clade, Foliaceo-bracteatae subclade]

        5 Bracts subtending the pedicels scarious (membranous), not foliaceous; [Larbreae clade, Parviflorae subclade]

      4 Inflorescences axillary, solitary or in small cymes of 2-5 flowers; seeds 0.3-0.8 mm long, distinctly papillose.

          6 Flowers in axillary inflorescences of 1-5 flowers; sepals 5; petals 5; seeds 0.3-0.4 mm long, with small, rounded tubercles; [widespread]; [Larbreae clade, Uliginosae subclade]

          6 Flowers solitary in leaf axils; sepals 4 (-5); petals absent; seeds 0.6-0.8 mm long, with stalked, knoblike tubercles; [of c. KY and TN]

    3 Sepals 3.5-9 mm long; petals 3.5-13 mm long, equaling or longer than the sepals; seeds 0.7-2.5 mm long.

             7 Seeds 2-2.5 mm long; bracts of the inflorescence herbaceous; petals notched < halfway to the base

             7 Seeds 0.7-1.2 mm long; bracts of the inflorescence scarious; petals notched > halfway to the base; [Larbreae clade].

               8 Sepals 4.5-5.5 (-7) mm long, strongly 3-nerved, narrowly lanceolate to triangular; leaves usually widest below the middle; seeds 0.8-1.2 mm long, coarsely tuberculate; inflorescence diffuse, many-flowered; [Gramineae subclade]

               8 Sepals (2-)3.5-4-5 mm long, weakly 3-nerved, ovate-elliptic; leaves usually widest at or above the middle; seeds 0.7-1.0 mm long, obscurely sculptured and appearing almost smooth; inflorescence more compact, fewer-flowered; [Parviflorae subclade]

  2 Leaves broad, usually ovate, obovate, or broadly elliptic, the blade 1-2.5× (or to 4×) as long as wide, 4-30 mm wide (if > 2.5× as long as wide, then definitely > 10 mm wide); stems terete or 4-angled.

                 9 Leaves long-petiolate, the petiole about as long as the blade, the blades cordate to truncate at the base; sepals 2.5-3.5 mm long, obtuse to broadly acute; seeds 0.6-0.8 mm long; stem glabrous or glandular-puberulent (the pubescence not in lines); [Petiolares clade]

                 9 Leaves sessile, short-petiolate, to long-petiolate (if long petiolate, the blades cuneate), the blades rounded to cuneate at the base; sepals 2.5-11 mm long, broadly acute to acuminate; seeds 0.4-2.0 mm long; stem puberulent to short-pilose (the pubescence in vertical lines or not).

                   10 Leaves (1.0-) 2.5-10 cm long (with strong dimorphism between sterile and fertile shoots, the leaves of sterile shoots much larger); seeds 1.7-2 mm long; sepals 4-11 mm long; stem pubescence in vertical lines or uniformly distributed; perennial, the stems strong and ascending to erect; [native]; [Insignes clade].

                     11 Sepals 7-11 (-12) mm long, acuminate, ciliate, but more-or-less glabrous on the back; [of the mountains]

                     11 Sepals 3.5-7 mm long, acute, ciliate and more-or-less pubescent on the back; [widespread in our area]

                   10 Leaves 0.3-4.0 cm long; seeds 0.6-1.7 mm long; sepals 2.5-6.5 mm long; stem pubescence always in vertical lines; annual, the stems weak and in part prostrate, the tips or vigorous growth ascending; [exotic]; [Petiolares clade].

                       12 Sepals 5.0-6.5 mm long; stamens 8-10; seeds 1.1-1.7 mm long

                       12 Sepals 2.5-5.2 (-6.0) mm long; stamens 1-5 (-8); seeds 0.4-1.3 mm long.

                          13 Stamens 3-5 (-8); sepals 4.5-5.2 (-6.0) mm long, lacking red band at base; seeds 0.9-1.4 mm long; petals usually present

                          13 Stamens 0-3 (-5); sepals 3.0-4.0 mm long, frequently with a red band at the base; seeds 0.4-0.9 mm long; petals usually absent

1 Petals absent; fruit a 1-seeded, indehiscent utricle; styles 2; [tribe Sclerantheae]

1 Petals present (rarely obsolete or essentially absent); fruit a few-many seeded capsule; styles 3-5.

  2 Leaves fleshy; seeds > 3 mm long; [of seabeaches and dunes] ; [tribe Sclerantheae]

  2 Leaves membranaceous or stiff; seeds < 2 mm long; [of various habitats].

    3 Styles 4-5.

      4 Leaves linear-subulate, < 2 mm wide; styles 4-5.

        5 Leaf bases not forming a scarious cup; valves or teeth of the capsule twice as many as the styles; [tribe Alsineae]

        5 Leaf bases usually forming a conspicuous scarious cup; valves or teeth of the capsule as many as the styles; [tribe Sagineae]

      4 Leaves ovate, obovate, > 4 mm wide; styles 5; [tribe Alsineae].

          6 Capsule cylindric, dehiscent by 10 apical teeth

    3 Styles 3.

             7 Inflorescence umbelliform; petals irregularly denticulate at apex; [tribe Alsineae]

             7 Inflorescence cymose or racemiform; petals entire, notched, or deeply cleft.

               8 Petals shallowly to deeply 2-cleft, notched at least 1/4 of the length, often divided nearly to the base and then appearing almost as 10 petals; [tribe Alsineae].

                 9 Capsule cylindric, twice as long as the sepals; petals 2-cleft 1/5 - 1/2 length; styles (3-) 5 (-6), 0.5-2 mm long

                 9 Capsule spherical, ellipsoid, or globose, as long as or slightly longer than the sepals; petals 2-cleft 2/3-3/4 length (1/2 length in Rabelera); styles (2-) 3 (-5), 0.2-7 mm long

                   10 Stems square; petals 2-cleft ca 1/2 of length

                   10 Stems round or roundish; petals 2-cleft 2/3 to 3/4 of length

               8 Petals entire, or emarginate.

                     11 Valves or teeth of the capsule as many as the styles.

                       12 Leaves strongly basally disposed, most in the lowermost 1/3 of the stem, and overlapping (the internodes < the leaf length; leaves firm, with axillary fascicles of leaves; [tribe Sagineae]

                       12 Leaves evenly distributed along the stem and widely spaced (the internodes > the leaf length); leaves herbaceous to slightly fleshy, generally without axillary fascicles of leaves.

                          13 Sepals 4; petals 0; [tribe Sagineae]

                          13 Sepals 5; petals 5; [tribe Sclerantheae]

                     11 Valves or teeth of the capsule twice as many as the styles.

                            14 Seeds with an aril; [tribe Arenarieae]

                            14 Seeds lacking an aril.

                              15 Capsule straight; petals entire or barely emarginated; [tribe Arenarieae]

                              15 Capsule cylindrical, and often somewhat curved; petals emarginate to bifid; [tribe Alsineae]