Annual herb ± 0.9–1.5 m., glabrous, much branched from near the base,with numerous, long and slender, divergent branches; stem fistular, it and the branches terete, striate, sometimes with a whitish bloom.. Basal leaves withered at time of flowering; lower stem leaf (only one seen) ± 18 × 12 cm., the lamina oblong-elliptic, bipinnate with 8 pairs of sessile pinnae, all pinnules but the lowest decurrent along the axis and ± fusing with the rest, margins irregularly sharply toothed, teeth with a long acute mucro; petiole rather short, composed mostly of the tapering, ridged sheath; median stem leaves similar but rapidly reducing with smaller and especially much narrower segments, soon becoming sessile; uppermost leaves very much reduced, very narrowly divided into ± setaceous segments; all sheaths with broad white-membranous margins.. Umbels numerous, with 6–10 glabrous rays 1.5–4 cm. long; involucre conspicuous, of ± 3–6 short to very long, 2–35 mm. glabrous bracts, narrowly linear or rarely one divided in a lower umbel; partial umbels 7–20-flowered; pedicels 1.5–6 mm., glabrous; involucel of 6–8 linear sharply mucronate bracteoles, 1.5–4 mm.; peduncles 4–9 cm., glabrous.. Calyx obsolete.. Petals white, obcordate to elliptic-oblong, ± 0.75–1 mm., prominently 1-vittate, glabrous; anthers pale yellow.. Fruit subrotund, ± 1.75–2 × 1.75–2.25 mm., as broad as or slightly broader than long, densely verrucose, ribs obscure; stylopodia very depressed-conical; styles slender but short, 1–1.5 times as long as the stylopodia and disk.. Fig. 15.
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