Iva asperifolia Less. var. angustifolia (Nutt.) B. L. Turner, narrow–leaf sumpweed. Annual, taprooted, 1–stemmed at base, not rosetted, erect principal axis with ascending branches mostly above midplant, in range 30—72 cm tall; monoecious; shoots with only cauline leaves, foliage ± scabrous and at flowering absent to midplant, short–strigose to short–hispid with upward–pointing hairs, gland–dotted with colorless heads uniformly distributed in depressions, pleasantly aromatic like Ambrosia.
Stems cylindric, in range to 2 mm diameter, tough, initially short–strigose and inconspicuously gland–dotted, main axis forming brownish periderm and becoming glabrescent.
Leaves opposite decussate to the lowest pair of lateral branches, helically alternate above, simple, short–petiolate and pairs not connected across node, without stipules; petiole shallowly channeled, to 5 mm long, having the longest hairs with enlarged bases along edges; blade linear to lanceolate–linear or narrowly lanceolate, in range < 6—30(—45) × 1.8—8.8 mm, tapered at base, entire, acute at tip, 1–veined or 3–veined from base with principal veins slightly sunken on upper surface and raised on lower surface.
Inflorescence heads, in terminal, leafy, spikelike arrays on main and lateral shoots, array erect to suberect, 55—80 × 4—5 mm, heads helically alternate, 20+, 1(—2) per node and stiffly nodding, head discoid, 2 mm across, in range each head with (0)1 disclike pistillate (peripheral) flower and 3 staminate (central) disc flowers, flowers nowshowy, bracteate, with nonglandular hairs and gland–dotted; main axis stemlike, pale yellowish green, with sparse nonglandular hairs; bract subtending peduncle leaflike, ascending or curved, linear, to 12 × 0.4—1 mm, ± rounded on back, short–ciliate with stiff hairs and having colorless glands; peduncle ± reflexed, ± bulbous, in range < 1 mm long, glabrous; involucre inversely pyramidal with 3—4 angles, in range 2—3 × 2 mm and slightly longer and wider in fruit, of 3—4 ± equal, phyllaries fused at least 2/3, green portion mostly keeled and connected by membranous panels as wide as green tissue, green tissue with some hairs and gland–dotted, lobes acute; receptacle flat and narrow, with bristlelike bractlets (paleae), palea inconspicuously barbed to above midpoint, 1.5—2 mm long, the threadlike portion ca. 0.05 mm diameter and expanded somewhat above midpoint to 0.1 mm diameter.
Peripheral flower pistillate, bilateral, ca. 2 mm long; calyx (pappus) absent; corolla inconspicuously and irregularly minutely several–toothed, narrowly funnel–shaped, in range 0.7—0.8 mm long, white, persistent around lower portion of style; stamens absent; pistil 1; ovary inferior, compressed–obovoid, pale green covered with darker green glands and becoming resinous, with some short hairs at the top, 1–chambered with 1 ovule; style eventually exserted to 1.5 mm above top of involucre, white, 2–branched, the lower portion 1 mm long, the branches unequal, linear, 1.2—1.5 mm long, thickened, minutely papillate and stigmatic on margins.
Central flower functionally staminate, radial, ± 1.5 mm across, 2—2.7 mm long; calyx (pappus) absent; corolla 5–lobed, ca. 1.6 mm long, white but lobes sometimes aging rose or purplish; tube ± cylindric, ca. 0.4 mm long; throat bell–shaped, ca. 0.8 mm long, with 5 veins to sinuses; lobes recurved, acute–triangular, 0.45—0.5 mm long; stamens 5, fused to corolla near base; filaments free, flattened front–to–back, ca. 0.6 mm long, white; anthers not fused, dehiscent while included in corolla later becoming exserted ca. 1 mm, basifixed, dithecal, ± 1.2 mm long including appendages, pale light yellow, with terminal appendage curved over anther sacs, the appendages triangular to ovate and acute, white or pinkish, longitudinally dehiscent; pollen light yellow; pistil with rudimentary ovary, ovary inferior, narrowly wedge–shaped, ca. 0.8 × 0.15 mm, green, glabrous; style and inconspicuous.
Fruit cypselae, obovoid, in range 2—2.8 mm long, plump or sometimes compressed front–to–back, deep burgundy drying black, resinous, with minutely warty glandular faces; pappus absent.
A. C. Gibson