Diodia virginiana L., butterweed.  Annual, taprooted, several–stemmed at base, in range prostrate to low–spreading; shoots ± 2–dimensional (plagiotropic), with only cauline leaves, glabrous.

Stems

Stems cylindric, to 3.5 mm diameter, at node with pair of ledges when leaves withered.

Leaves

Leaves opposite decussate, simple, sessile with sheath and fused across node, with stipules; stipules 2 between pair, sheath 2—2.5 mm long and expanded at base, 3–forked above, 6—7 mm long, central lobe 4—5.5 mm long with several hairs at tip, lateral lobes bristlelike and diverging at 45°, 2.5—3.5 mm long, hairs somewhat tufted approaching tip; blade narrowly elliptic or elliptic to narrowly oblanceolate or narrowly ovate, (< 5—)7—38 × < 3—10 mm, tapered to long–tapered at base, minutely toothed on margins, acute at tip, pinnately veined with midrib raised on lower surface, lateral veins paired.

Inflorescence

Inflorescence solitary, axillary and only 1 per node with a new unexpanded axillary shoot on upper side of shoot, ovary concealed by leaf sheath and ovary and fruit expanding and eventually breaking leaf sheath; bractlets subtending flower and partially encircling ovary 2, = a diminutive pair of stipules < 1.5 mm long, each bractlet 3–forked, the lobes mostly colorless but often purple–red at tips.

Flower

Flower bisexual, radial, ca. 7 mm across; hypanthium 0.3—0.4 mm long, short–fringed with 2 calyx lobes missing; calyx deeply 2–lobed, lobes ascending, narrowly lanceolate folded inward from midvein, 4—4.5 × 0.8—1 mm, subequal to unequal, green with purplish red along midvein, acute at tip, short–ciliate on margins; corolla 4–lobed, white; tube curved away from stem, 4.5—5 × 0.7—0.9 mm, glabrous on outer surface; lobes lanceolate, 3—4 × 1.5—1.7 mm, thickish, with scattered hairs on upper surface or continued from tube; stamens 4, arising from near top of corolla tube opposite sinuses; filaments exserted, 2.2—2.4 mm long, white; anthers dorsifixed, dithecal, ± 1.7 mm long, white, longitudinally dehiscent; pollen white; pistil 1, appressed to stem internode; ovary inferior, 2–lobed, each part hemi–ellipsoid, 2.5 × 2 × 1—1.2 mm, light green, glabrous, 2–chambered, each chamber with 1 ovule; style slender, ca. 11 mm long, 2–branched, the branches stigmatic, threadlike, 4+ mm long

Fruit

Fruit schizocarpic of 2 mericarps, ± ellipsoid to ellipsoid–ovoid, 6.5—7.8 × 4—4.5 mm, with 2 erect calyx lobes to 5 mm long, aging 8–ribbed and corky, with scattered short hairs along ribs above midpoint, having minute dark hairs above midpoint.

A. C. Gibson