Heliotropium tenellum (Nutt.) Torrey, pasture heliotrope. Annual, taprooted, 1–stemmed at base, not rosetted, erect with spreading branches from principal axis above midplant, in range to 30 cm tall; shoots with only cauline leaves, strigose and short–strigose with appressed, upward–pointing hairs.
Stems cylindric, to 2 mm diameter, tough and wiry, lower stem exfoliating surface with hairs.
Leaves helically alternate, simple, short–petiolate, without stipules; petiole to 2 mm long; blade linear, 10—25(—45) × 0.9—1.5(—5) mm, entire with inrolled margins (revolute), acute at tip, 1–veined with midrib sunken on upper surface and raised on lower surface, lower surface densely strigose with upward–pointing hairs
Inflorescence cyme, racemelike, several–flowered, terminal, not bracteate, green tissue densely strigose with upward–pointing hairs; peduncle < 0.7 mm diameter; pedicel to 6 mm long.
Flower bisexual, radial, 9—9.5 mm across; calyx unequally 5–lobed, densely strigose with upward–pointing hairs; tube short; lobes scarcely fused at base, ascending, narrowly triangular, the longest lobe 5—7.3 × to 1.2 mm, the shortest lobes < 3 × 0.4 mm, dark green, 1–veined, not inrolled, strigose on both surfaces; corolla 5–lobed, trumpet–shaped (salverform), 8.6—9 mm long, ca. 4 mm green to green–yellow and short–hairy and white above, in bud exposed corolla cream–colored; tube cylindric, lower portion 0.4 × 0.7 mm, pale green and glabrous, upper portion 0.8 mm long, densely short–hairy; throat with lower portion expanded around anthers, above anthers narrowed and 5–ridged, flaring upper portion white, inside with a set of short hairs at the base of each stamen; lobes broadly elliptic to ovate, 3.1—4 × 2.2—2.3 mm, white, flaring upper throat and lobes with stripe of strigose hairs on lower surface; stamens 5, fused at top of corolla tube 1.2 mm from base, sessile; anthers basifixed, dithecal, 1 mm long, white, minutely hairy subterminal on inner side, longitudinally dehiscent; pollen white; pistil 1, 1.3—1.5 mm long; ovary superior, 4–lobed, ca. 0.5 × 0.5 mm, green, at anthesis without hairs (beaded above midpoint), 4–chambered, each chamber with 1 ovule; style 0.9 mm long, enlarged above base (to 0.4 mm diameter), 2–branched, green below fork, the branches erect, acute, 0.25 mm long, white, and stigmatic.
Fruit nutlets, 4, intact width > length, with erect style; nutlets 3–sided rounded on back, ± 1.5 mm long, gray–brown with darker ribs, densely short–hairy; calyx with unequal lobes, < 3—11 mm long.
A. C. Gibson