Diodia teres Walter, rough buttonweed, poor joe. Annual, taprooted, several–stemmed at base, branching opposite decussate, in range to 28 cm tall; shoots with only cauline leaves, foliage scabrous with short, sharp–pointed hairs.

Stems

Stems somewhat 4–sided (especially at node), to 2 mm diameter, internodes to 38 mm long and streaked red, compressed side–to–side approaching node, with scattered long hairs to 2.2 mm long and curved short hairs.

Leaves

Leaves opposite decussate, simple, sessile, with stipules; stipules = white bristles on stem node, 3—7 per side on flap between leaves, (1—)6(—11) mm long; blade narrowly lanceolate to narrowly elliptic, 13—36 × < 4—10 mm, tapered at base, entire but scabrous on margins, acute with fine point at tip, pinnately veined with midrib sunken on upper surface and raised on lower surface.

Inflorescence

Inflorescence flowers solitary, axillary and only 1 per node, flower sessile

Flower

Flower bisexual, ± radial, ca 4 mm across; sepals 4, opposite decussate and not obviously fused, dimorphic, ascending, ovate, 2—2.2 × 0.9 mm (outer pair) and 1—1.8 mm long (lateral pair), short–toothed ciliate, acute at tip, inconspicuously veined, having several short hairs on lower (outer) surface; corolla 4–lobed, light blue–violet; tube + throat cylindric, 4 mm long, white at base; lobes widely spreading, triangular, 2 × 1.2—1.3 mm, acute at tip, with short hairs on lower surface; stamens 4, fused to corolla at sinuses; filaments ± 0.6 mm long, white; anthers dorsifixed, dithecal, 0.8 mm long, white, longitudinally dehiscent; pollen white; pistil 1; ovary inferior, 2–lobed, pyramidal wedge–shaped, 1 mm long, green, with appressed stiff hairs, 2–chambered, each chamber with 1 ovule; nectary disc at top of ovary surrounding style; style erect, ca. 5 mm long, white; stigma terminal, exserted, umbrellalike (peltate), 0.8 mm across, violet.

Fruit

Fruit schizocarp splitting into 2 dry mericarps, before splitting top–shaped, ca. 4 × 3.5 mm, with 1—3 sepals attached to each mericarp, sepals to 3 mm long; mericarps hemi–ovoid, ca. 4 × 2.6—2.8 × 2 mm, with long hairs above midpoint and having appressed, upward–pointing short hairs.

A. C. Gibson