Herbs, perennial or annual, spreading. Stems decumbent to scandent. Leaves: blade narrowly lanceolate to lanceolate-oblong, lanceolate-elliptic or ovate, 1.5--14 × 0.5--3.3 cm, margins scabrous, apex acute to acuminate, glabrous. Inflorescences: distal cyme 1--several-flowered, usually exserted; spathes solitary, bright green, without contrasting veins, pedunculate, usually distinctly falcate, (0.5--)0.8--4 ´ 0.4--1.2(--1.4) cm, margins distinct, glabrous or scabrous, sometimes also sparsely ciliate or ciliolate basally, apex usually acuminate, usually glabrous or nearly so; peduncles 0.5--2(--4) cm. Flowers bisexual and staminate; petals all blue (rarely all lavender), proximal petal smaller; medial stamen anther connective usually with transverse band of violet; staminodes 2--3; antherodes yellow, medial often absent or vestigial, cruciform. Capsules 3-locular, 2-valved, 4--6.3 mm. Seeds 5 (or less through abortion), brown, 2--2.8(--3.2) ´ 1.4--1.8 mm, deeply reticulate.
The name Commelina nudiflora Linnaeus has been incorrectly used for this species.
Fibrous-rooted annual, diffusely branched, decumbent and rooting from the lower nodes, to 1 m; lf-blades lanceolate, the larger 3-8(-11) נ1-1.5(-2) cm; sheaths 0.5-1 cm; spathe (folded) semicordate and ±falcate, 1.5-2.5 cm, nearly as wide, acute or short-acuminate, glabrous or finely ciliate, its margins free, its stalk 1-2 cm; larger spathes usually with a 1-few-fld upper cyme in addition to the well developed lower one; blade of upper pet 6-8 mm; lower median pet blue; anthers 5 or 6 (2 or 3 sterile); fr 3-locular, the lower locules each 2-seeded, the upper one 1-seeded; seeds of the lower locules 2-2.8(-3.2) mm, deeply reticulate; 2n=28-60. Wet woods and river-banks; native to the Old World, only intr. in N. Amer., where mainly in se. U.S., n. sometimes to Del., O., Ill., Minn., and Kans.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.