1 Flowers sessile, axillary; plants to 4 cm tall; petals absent; sepals fused into a cuplike hypanthium

1 Flowers either (1-) 5-50+ in terminal corymbose cymes, or if solitary and axillary on pedicels 10-40 mm long; petals present or (in Sabulina fontinalis) absent; sepals separate.

..2 Flowers (1-) 5-50+ in terminal corymbose cymes; petals present.

....3 Sepals acute to acuminate at the tip; sepal venation prominently 3- or 5-veined, or (in Geocarpon nuttallii) obscure.

......4 Plants perennial from woody crowns; leaves rigid, with axillary fascicles; pedicels glabrous

......4 Plants either annual or perennial from slender wintering stems; leaves flexuous, lacking axillary fascicles; pedicels sparsely to densely stipitate-glandular.

........5 Stems prostrate or decumbent, leafy throughout; [of moist habitats]

........5 Stems erect, leafy mostly near the base, the stem leaves few in number and reduced in size upward; [of moist to dry upland habitats].

..........6 Sepals 3-nerved; leaves narrowly lanceolate to narrowly oblanceolate, (0.6-) 1.5-3.2 mm wide; seeds 0.7-0.9 mm long, the surface appearing pebbled or with short papillae, black

..........6 Sepals 5-nerved or 5-ribbed; leaves narrowly oblinear to linear, 0.5-1.5 (-1.8) mm wide; seeds 0.5-0.7 mm long, the surface tuberculate, reddish brown to black

....3 Sepals obtuse or rounded at the tip; sepal venation obscure.

............ 7 Leaves rigid, closely imbricated, with axillary fascicles of leaves; pedicels densely stipitate-glandular; plants perennial from a very long and deep, woody taproot; [xeric sands; Coastal Plain NY to FL Panhandle]

............ 7 Leaves flexuous, not imbricated, lacking axillary fascicles of leaves; pedicels either glabrous or (in Geocarpon nuttallii) stipitate-glandular; plants either annual or perennial from a basal mat of offshoots, taproots filiform; [thin soils over rock outcrops; inland provinces].

............ ..8 Pedicels stipitate-glandular; [west of the Mississippi River in AR, LA, OK, and TX]

............ ..8 Pedicels glabrous; [east of the Mississippi River].

............ ....9 Leaves oblanceolate, 1-3 mm wide, very thin in texture and prominently though minutely veined; flowers in cymes of mostly 1-3 flowers; [shaded Cumberland Plateau rockhouses of s. KY and n. TN]

............ ....9 Leaves linear, mostly < 1 mm wide, thicker in texture, then veins not readily apparent; flowers in cymes of mostly 3-25+ flowers; [collectively of sunny thin-soil-over-rock habitats of the Piedmont and Appalachians].

............ ......10 Seeds 0.4-0.6 mm long, suborbicular, lacking an adaxial groove; petals oblanceolate, not clawed

............ ......10 Seeds 0.5-0.8 mm long, obliquely triangular, with an adaxial groove; petals clawed, broadly obovate.

............ ........11 Plants annual, 10-20 cm tall (thus populations often consisting of many single stemmed individuals); cymes mostly 9-15-flowered; sepals 3-4 mm long; petals 4-6 (-8) mm long; [of Piedmont and low mountain granitic flatrocks and other outcrops]

............ ........11 Plants perennial from a basal mat of offshoots, 5-10 (-15) cm tall (thus populations often consisting of multi-stemmed clumps); cymes mostly 3-7-flowered; sepals 3.5-5.5 mm long; petals 6-10 mm long; [of mountain peaks and Piedmont monadnocks]

1 Flowers (1-) 5-50+ in terminal corymbose cymes; petals present.

..2 Stems prostrate or decumbent, leafy throughout; [of moist habitats]

..2 Stems erect, leafy mostly near the base, the stem leaves few in number and reduced in size upward; [of moist to dry upland habitats].

....3 Seed surface pebbled-papillose; mature leaves narrowly lanceolate or oblanceolate, 1.5-3 mm wide; sepal nerves 3

....3 Seed surface tuberculate with low ridges, resembling a brain; mature leaves linear, < 1.5 mm wide; sepal nerves 3 or 5.

......4 Plants perennial from woody crowns; leaves rigid, with axillary fascicles; stem and inflorescence axes strictly glabrous; sepal nerves 3

......4 Plants either annual or perennial from slender wintering stems; leaves flexuous, lacking axillary fascicles; stem and inflorescence variously stipitate-glandular to glabrous, sepal nerves 3 or 5.

........5 Sepal nerves 3 (occasionally weakly 5), widely spaced, not appearing ribbed; inflorescences divaricately-branching at maturity, forming a diffuse tangled mound in robust specimens; seeds 0.8-0.9 mm across; flowering time centered May through June

........5 Sepal nerves 5, typically closely spaced and appearing elevated and ribbed (widely spaced in some specimens); inflorescences ascending to spreading at maturity; seeds 0.5-0.7 (-0.75) mm across; flowering time centered April through May

1 Styles 5 (-6); capsule opening by 5 (-6) shallowly bifid valves

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]

....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