Herbs, perennial or annual. Roots thin or tuberous. Leaves 2-ranked or spirally arranged, not glaucous; blade sessile or petiolate. Inflorescences terminal, leaf-opposed; cymes 1–2, enclosed in spathes, proximal cyme several-flowered, distal cyme vestigial or with 1–several staminate flowers; spathes often filled with mucilaginous liquid, margins distinct or basally connate; bracteoles usually absent. Flowers bisexual and staminate, bilaterally symmetric; pedicels well developed; sepals distinct or proximal 2 connate, unequal; petals distinct, proximal petal often different color than distal 2, smaller or subequal, distal 2 blue (occasionally lilac, lavender, yellow, peach, apricot, or white), clawed; stamens (5–)6, proximal 3 fertile, medial different in form, size from others, distal (2–)3 staminodial; filaments glabrous; antherodes commonly 4–6-lobed; ovary 2–3-locular, ovules 1–2 per locule, 1-seriate. Capsules 2–3-valved, 2–3-locular. Seeds 1–2 per locule; hilum linear; embryotega lateral. x = 11–15.

Distribution

Almost worldwide, mainly tropical.

Discussion

Species ca. 170 (9 in the flora).

Selected References

Brashier, C. K. 1966. A revision of Commelina (Plum.) L. in the U.S.A. Bull. Torrey Bot. Club 93: 1--19.

Faden, R. B. 1993b. The misconstrued and rare species of Commelina (Commelinaceae) in the eastern United States. Ann. Missouri Bot. Gard. 80: 208--218.

Pennell, F. W. 1916. Notes on plants of the southern United States—I. Bull. Torrey Bot. Club 43: 96--111.

Lower Taxa

Commelina benghalensis, Commelina caroliniana, Commelina communis, Commelina dianthifolia, Commelina diffusa, Commelina erecta, Commelina forskaolii, Commelina gambiae, Commelina virginica

Key

1	Spathes with margins distinct to base.	> 2
1	Spathes with margins connate basally.	> 5
2	Perennials with erect to ascending stems; roots tuberous; leaves linear to linear-lanceolate	Commelina dianthifolia
2	Annuals or perennials usually with decumbent to scandent stems; leaves narrowly lanceolate to ovate-elliptic.	> 3
3	Spathes generally whitish or pale green toward peduncle with contrasting, dark green veins; proximal petal white or paler than others; capsules 2-locular; seeds rugose pitted-reticulate	Commelina communis
3	Spathes without contrasting veins; proximal petal ± concolorous with others; capsules 3-locular; seeds reticulate or smooth to faintly alveolate.	> 4
4	Spathes not at all to slightly falcate; distal cyme usually vestigial (rarely well developed, 1-flowered); seeds smooth to faintly alveolate	Commelina caroliniana
4	Spathes usually distinctly falcate; distal cyme in larger spathes usually well developed, 1–several-flowered; seeds reticulate	Commelina diffusa
5	Flowers apricot- or peach-colored	Commelina gambiae
5	Flowers blue (rarely lilac to lavender or white).	> 6
6	Leaf sheaths with auricles at summit; roots stout; proximal petal white, minute; locules all 1-seeded	Commelina erecta
6	Leaf sheaths not auriculate; roots thin; proximal petal blue to lilac or lavender, conspicuous; some locules usually 2-seeded.	> 7
7	Perennials with erect to ascending stems; leaf sheaths with red hairs at summit; leaf blades 6–20 cm; spathes 1.5–3.5 cm; subterranean, cleistogamous flowers absent	Commelina virginica
7	Annuals or perennials with ascending to decumbent, repent or scrambling stems; sheaths with or without red hairs at summit; leaf blades 1.5–7(–9) cm; spathes 0.5–2 cm; subterranean, cleistogamous flowers sometimes present.	> 8
8	Leaf blades ovate to lanceolate-elliptic; sheaths often with red hairs at summit; lateral stamen filaments not winged; capsules usually 5-seeded	Commelina benghalensis
8	Leaf blades oblong to lanceolate-oblong or oblong-elliptic; sheaths without red hairs; lateral stamen filaments winged; capsules usually 1-seeded	Commelina forskaolii