Herbs, perennial. Roots fleshy, stout, tufted. Stems cespitose, usually erect to ascending (rarely decumbent, rooting at nodes). Leaves: leaf sheath auriculate at apex; blade sessile or petiolate, linear to lanceolate (rarely lanceolate-ovate), 5--15 ´ 0.3--4 cm, apex acuminate (rarely acute). Inflorescences: distal cyme vestigial, included; spathes solitary or clustered, green, pedunculate, not at all to strongly falcate, 1--2.5(--4) ´ 0.7--1.5(--2.5) cm, margins longly connate, glabrous except along connate edge, apex acute to acuminate, sometimes purple, usually variously pubescent; peduncles 0.5--1(--2) cm. Flowers bisexual and staminate, 1.5--4 cm wide; proximal petal minute, white, distal petals blue (rarely lavender or white); staminodes 3, staminodes and medial stamen entirely yellow; antherodes cruciform. Capsules 3-locular, 2-valved (very rarely 3-valved), 3.5--4.5 ´ 3--5 mm; abaxial locule warty, indehiscent (very rarely smooth and dehiscent); adaxial locules smooth, dehiscent. Seeds 3, brown, with soft, whitish tissue at both ends or in a band, 2.4--3.5 ´ 2.3--2.8 mm, nearly smooth. 2n = 60. Flowering spring--fall. Rocky woods and hillsides, scrub oak woods, pine woods and barrens, sand dunes, hummocks, shale barrens, roadsides, railroad rights-of-way, fields, and occasionally a weed in cultivated ground; Ala., Ark., Ariz., Colo., Del., D.C., Fla., Ga., Ill., Ind., Iowa, Kans., Ky., La., Md., Miss., Mo., Nebr., N.C., N.J., N.Mex., N.Y., Okla., Pa., S.C., Tenn., Tex., Va., W.Va., Wis.; Central America. Commelina erecta grows in temperate regions of North and Central America, as well as in tropical regions. This is by far the most variable species of Commelina in the flora. Three freely intergrading varieties may be recognized, although they are of questionable significance: C. erecta var. erecta, with larger leaves lanceolate to lanceolate-ovate, (1.5--)2--4 cm wide, and spathes (2.2--)2.5--3.6 cm, occurs throughout our region; C. erecta var. angustifolia (Michaux) Fernald, with leaves linear to narrowly lanceolate, 0.3--1.5 cm wide, and spathes 1--2 cm, is mainly southern but extends as far north as Virginia; and C. erecta var. deamiana Fernald, with leaves linear to narrowly lanceolate, 0.5--1.7 cm wide, and spathes 2--3.5 cm, occurs in midwestern United States south to Texas.
Perennial from a cluster of thickened fibrous roots; stems erect or ascending, to 1 m, usually branched; principal lvs linear to lanceolate, 4-15 נ0.5-4 cm, the sheaths white-ciliate, somewhat prolonged at the summit into rounded, often flaring auricles; spathes arising near the summit of the culm, solitary or in small clusters, short-peduncled, broadly semi-deltoid, often with conspicuous radiating cross-veins, the margins connate in the lower third, upper pet 10-25 mm, the lower one much smaller and white; 2n=56-120. Dry, usually sandy soil; s. N.Y. to Pa., O., Mich., se. Minn., Io., and Wyo., s. to S. Amer.; also Old World. Highly variable, but only with difficulty divisible into vars. Var. erecta (C. virginica, misapplied; C. elegans), with lanceolate or lance-ovate lvs 10-15 ױ.5-4 cm, and with the spathes glabrous or nearly so, is mainly Ozarkian (with us), but extends Ҵhroughout the range of the sp. Var. angustifolia (Mich.) Fernald (incl. C. crispa), with linear lvs 4-10cm and small spathes 1-2 cm, centers in Tex., but extends irregularly into our range. Var. deamiana Fernald, with linear lvs 10-15 cm, the spathes 2.5-3.5 cm and often pilose at base, occurs mainly on sand dunes from Ind. and s. Mich. to Neb., occasionally s. and w. to Tex. and Ariz.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.