Sp. Pl. 1: 40. 1753; Gen. Pl. ed.; 5:25, 1754.
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.
Almost worldwide, mainly tropical.
Species ca. 170 (9 in the flora).
|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|