This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol3", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Perennial, glabrous, fleshy, glaucous, branched, 1° - 1 1/2° high, the branches ascending. Leaves spatulate, indistinctly veined, 2' long or less, obtuse at the apex; scorpioid spikes 2-5; flowers 3"-4" broad, white, or bluish; calyx-segments ovate-lanceolate, acute; fruit rather larger than that of H. curassavicum.
Prairies, plains and meadows, Iowa to North Dakota, Assiniboia, Chihuahua and California. June-Sept.
5: 188. 1833-37. H. tenellum Torr. in Marcy's Rep. 304. pl. 14. 1853.
Annual, strigose-canescent; stem erect, slender, paniculately branched, commonly leafless below, 6-18' high. Leaves linear, entire, 1/2'-1 1/2' long, 1"- 2" wide, narrowed at both ends, sessile, or the lower petioled; flowers white, about 2\" long, sessile at the ends of short lateral branches, bracted by 1 or 2 leaves; calyx-segments unequal, the 2 or 3 larger ones about as long as the corolla; corolla-tube canes-cent, slightly longer than the limb, its lobes entire; anthers obtuse; stigma subulate-tipped; fruit depressed, 4- lobed, strigose-pubescent, separating into 4 1-seeded nutlets.
In dry soil, Kentucky to Kansas, south to Alabama, Texas and New Mexico. April-Aug.
Enploca convolvulacea Nutt. Trans. Am. Phil. Soc. (II.)
Annual, strigose-canescent, usually much branched, 6'-15' high, the branches ascending. Leaves oblong, ovate, or lanceolate, entire, short-petioled, obtuse or acute at the apex, narrowed at the base, 1/2'-1 1/2' long; flowers numerous, fragrant, very short-peduncled, terminal and lateral, mostly solitary and opposite the leaves; calyx-segments lanceolate, acuminate, equal; corolla white, strigose, 8"-10" long, about 6" broad, its tube narrowed at the throat, longer than the calyx and the angulate-lobed limb; anthers inserted on the tube of the corolla, slightly cohering by their tips; style filiform; stigma with a tuft of bristly hairs; fruit 2- lobed, pubescent, each lobe splitting into 2 1-seeded nutlets.
In dry sandy soil, Nebraska to Texas, Utah and Mexico. July-Sept.
Heliotropium indicum L. Sp. Pl. 134. 1753.
Annual, more or less hirsute or hispid; stem commonly branched, 1°-3° high. Leaves ovate or oval, obtuse or acute at the apex, obtuse rounded or sub-cordate at the base, 2'-6' long, 1'-3 1/2' wide, repand or undulate, borne on margined petioles 1/2'-21/2' long; flowers blue, 2"-3' broad, sessile in terminal dense bractless usually solitary scorpioid spikes which become 3'-6' long in fruit; calyx-segments lanceolate, acute, shorter than the strigose corolla-tube; style very short, deciduous; fruit deeply 2-lobed, glabrous, the lobes divergent, each finally splitting into 2 nutlets, each of which is ribbed on the back.
In waste places, North Carolina to Kentucky, Illinois, Missouri, Florida and Texas. Naturalized from India. Also in ballast about the northern seaports. Widely distributed in warm regions as a weed. Turnsole. May-Nov.