Calyx 4-lobed, persistent; the lobes in fruit distant. Corolla salver-form or funnel-form, usually much longer than the calyx-lobes, 4-lobed, the lobes valvate in the bud. Stamens 4; anthers linear or oblong. Style 1; stigmas 2. Ovary 2-celled. Pod top-shaped, globular, or didymous, thin, its summit or upper half free from and projecting beyond the tube of the calyx, loculicidal across the top. Seeds rather few (4–20 in each cell), peltate and saucer-shaped or globular-thimble-shaped, pitted.—Small herbs, with short entire stipules connecting the petioles or narrowed bases of the leaves, and cymose or solitary and peduncled flowers. These are dimorphous, in some individuals with exserted anthers and short included style; in others the anthers included and the style long, the stigmas therefore protruding. (Named for Dr. Wm. Houston, an English botanist who collected in Central America.)
[*] Small and delicate, vernal-flowering; peduncles 1-flowered; corolla salver-form; upper half of the broad and somewhat 2-lobed pod free; seeds globular, with a very deep round cavity occupying the inner face.
[+] Perennial by delicate filiform creeping rootstocks or creeping stems; peduncles filiform, 1–2´ long.
1. H. cærùlea, L. (Bluets. Innocence.) Glabrous; stems erect, slender, sparingly branched from the base (3–5´ high); leaves oblong-spatulate (3–4´´ long); peduncle filiform, erect; corolla light blue, pale lilac or nearly white with a yellowish eye, with tube much longer than its lobes or than those of the calyx.—Moist and grassy places, N. Eng. to Ga., west to Mich. and Ala.; producing from early spring to midsummer its delicate little flowers.
2. H. serpyllifòlia, Michx. Like the last, but filiform stems prostrate, extensively creeping and rooting; leaves orbicular to ovate (2–4´´ long); corolla rather larger, and deep violet-blue.—Along streamlets and on mountain-tops, Va. to Tenn. and S. C.
[+][+] Winter-annuals, branching from the simple root; peduncles much shorter.
3. H. pàtens, Ell. An inch to at length a span high, with ascending branches and erect peduncles; leaves spatulate to ovate; corolla much smaller than that of n. 1, violet-blue or purplish without yellowish eye, the tube longer than its lobes, twice the length of the calyx-lobes.—Dry or sandy soil, S. Va. to Tex. and Ill. (?)
4. H. mínima, Beck. More diffuse, commonly scabrous; stems at length much branched and spreading (1–4´ high); lowest leaves ovate or spatulate, the upper oblong or nearly linear; earlier peduncles elongated and spreading in fruit, the later ones short; tube of the purplish corolla not longer than its lobes or the ample calyx-lobes (1½´´ long).—Dry hills, Mo. to Tex. March–May.
[*][*] Erect, mostly perennial herbs (6–20´ high), with stem-leaves sessile, and flowers in small terminal cymes or clusters; corolla funnel-form, purplish, often hairy inside; seeds meniscoidal, with a ridge across the hollowed inner face.
5. H. purpùrea, L. Pubescent or smooth (8–15´ high); leaves varying from roundish-ovate to lanceolate, 3–5-ribbed; calyx-lobes longer than the half-free globular pod.—Woodlands, Md. to Ark., and southward. May–July.—Varying wonderfully, as into—