Iva annua L., seacoast sumpweed, sharp–bracted sumpweed, pelocote. Annual, taprooted, 1–stemmed at base, not rosetted, erect principal axis having paired, ascending branches mostly above midplant, in range 20—170 cm tall; monoecious; shoots with only cauline leaves, foliage scabrous with stiff, upward–pointing short hairs, gland–dotted with colorless heads uniformly distributed in depressions, pleasantly aromatic like Ambrosia.
Stems 6–ridged, in range to 13 mm diameter, with 3 ridges descending from each leaf, tough, internodes to 110 mm long, exposed side often red–purple, hairs upward–pointing aging with bases persistent; lower stem rigid, bark dull brown with ringlike scar at each node; pith narrow.
Leaves opposite decussate but helically alternate in flowering canopy, simple, petiolate having pairs fused across node, without stipules; petiole deeply channeled, to 33 mm long, ridged and grooved on lower side, with raised glands along ridges; blade ovate, 18—105 × (8—)14—70 mm, tapered to broadly tapered or subtruncate at base, low–serrate on margins with several widely spaced teeth per edge, < 12 teeth per blade, the teeth obtuse with a callus, somewhat swollen point at end of vein, acute to acuminate at tip, blade appear somewhat channeled at base on upper surface, 3–veined at base with principal veins raised on the lower surface.
Inflorescence heads, in terminal on main axis and lateral branches, leafy, spikelike arrays, array erect to suberect or ascending, < 30—150+ × 7—12 mm, heads helically alternate, 25+, 1 per node and stiffly nodding, head discoid, 3—5 mm across, in range each head with 3 disclike pistillate (peripheral) flowers, each subtended by a phyllary at its midpoint, and in range 12+ staminate (central) disc flowers, flowers nonshowy, bracteate, with nonglandular hairs and gland–dotted; main axis stemlike, somewhat ridged, tough, yellowish green, pubescent; bract subtending peduncle leaflike, ascending and partially concealing head, acuminate–ovate, < 6—20 × < 3—5.5 mm decreasing upward, tapered at base, entire, 3–veined with veins raised on lower surface; involucre hemispheroid, in range of 3 unequal, cupped phyllaries not fused, ca. 3 mm long, ciliate on margin, green mottled with colorless veins, the widest on outer side broadly obovate to top–shaped and 3—5 mm wide, truncate at top, to the outside of inner, narrower lateral phyllaries 2—3 mm wide, not keeled, pubescent and gland–dotted; receptacle low–domed, with flattened, oblanceolate–linear bractlets (paleae) long–tapered to base, in range 2.5—2.8 mm long, colorless aging red purplish, with orangish knobs (glands) along axis and tip with glandular hairs, palea slightly longer than staminate flower bud.
Peripheral flower pistillate, bilateral, ca. 0.9 mm across, 2.5 mm long; calyx (pappus) absent; corolla inconspicuously and irregularly minutely several–toothed, narrowly tubular, in range ca. 1 × 0.3 mm, white, with glandular hairs, persistent around lower portion of style; stamens absent; pistil 1; ovary inferior, ± trapezoidal compressed front–to–back, ± 0.8 × 0.9 mm, white, with short hairs especially at the top, 1–chambered with 1 ovule; style ca. 2 mm long, 2–branched at midpoint with branches exserted above corolla, white, the branches linear, minutely papillate and stigmatic on margins
Central flower functionally staminate, radial, 1 mm across; calyx (pappus) absent; corolla 5–lobed, to 2.5 mm long; tube curved and narrowly funnel–shaped, 1 mm long; throat abruptly expanded from tube, bell–shaped, ca. 1 × 1 mm, colorless or with minute reddish spots at base; lobes deltate, 0.5 mm, colorless aging red–purple and inrolled, with glandular hairs in bud; stamens 5, fused to corolla near base; filaments free, 0.4—0.5 mm long eventually elongating to push anthers out of corolla, colorless; anthers not fused, dehiscent while included in corolla later exserted, basifixed, dithecal, ± 1.4 mm long including deltate appendages 0.2—0.25 mm long, pale light yellow with colorless appendages, longitudinally dehiscent; pollen copious, pale light yellow, dry; pistil = a vestigial, cylindrc inferior ovary 0.1 mm beneath corolla.
Fruits cypselae, 3, of different ages per head, each with phyllary, obovoid, 2.3—2.8 × 1.7—2.3 mm, plump and compressed front–to–back, glossy black, resinous, with minutely warty glandular faces; pappus absent.
A. C. Gibson