Herbs, perennial, to 75(-100) cm tall. Stems leafy, glabrescent below, simple or with ascending branches from above middle. Leaves opposite below, alternate on branches, petiolate below, upper sessile; petiole 1-3 cm; blade ovate in outline, 4-10 × (2-)4-9 cm, 1 or 2 times pinnatisect, large segments 2-4 cm, divergent or ascending, linear or elliptic-oblong, central rachis 2-6 mm wide. Synflorescences terminal, spiciform, 10-20 cm × ca. 10 mm, usually surrounded by smaller secondary spikes terminating axillary branches, spike primarily of 50-100 male capitula. Male capitula: involucre cup-shaped or turbinate, 3-5 mm in diam.; paleae filiform, apices expanded and pubescent; florets 15-25; corollas pale yellow or greenish yellow, 2-2.5 mm; anthers white, inflexed-subulate, bases obtuse. Female capitula few and inconspicuous, solitary or 2-5 together in sessile leafy-bracteate axillary clusters on nodes beneath male part of spike; floret 1. Bur ± obovoid, 3-4 mm (including beak), 2-3 mm wide including blunt spines, spines 0.5-0.8 mm and thick, body rounded and coarsely reticulate above spines, beak tapering, 0.7-1 mm.
Perennials, 10–60(–100+) cm. Stems erect. Leaves proximally opposite, distally alternate; petioles 0–25 mm (often ± winged); blades deltate to lanceolate, 20–60(–140) × 8–35(–50+) mm, pinnately toothed to 1-pinnately lobed, bases cuneate to truncate, ultimate margins entire or toothed, abaxial and adaxial faces hirsutulous to strigose and gland-dotted. Pistillate heads clustered, proximal to staminates; florets 1. Staminate heads: peduncles 0.5–2 mm; involucres obliquely cup-shaped, 2–4(–5) mm diam., hirsutulous; florets 5–15(–30+). Burs: bodies ± obpyramidal to globose, 2–3 mm, hirsutulous, spines or tubercles 0 or 1–6, mostly distal, stoutly conic to acerose, (0.1–)0.5–1 mm, tips straight. 2n = 18, 27, 36, 45, 54, 63, 72, 100–104, 108, 144.
Mr. A.J.C. Grierson, Royal Botanic Garden, Edinburgh, to whom I am indebted for determinations and other assistance, tells me that a chromosome count of 2n = 108 in a specimen from Durban establishes this plant as the true Western America form of A. psilostachya. It is possibly a recent introduction to Natal and is so far known only from the sandy soils of the Durban Berea, Bayhead and nearby Isipingo Flats.
Perennial herb, up to 1 m high. Stems simple, arising from underground runners. Leaves mostly opposite; blade ovate in outline, bipinnatisect, ultimate leaf segments narrowly oblong, on average < 2 mm wide, lobe apices acute to acuminate, lobe margins entire or minutely dentate, pubescent, light green, somewhat aromatic; petiole ± 10 mm long. Heads unisexual; male heads small, drooping, in slender, terminal racemes up to 120 mm long, arranged in panicles, involucral bracts connate, cup-shaped, containing several, functionally male florets; female heads solitary or 2 or 3 together in leaf axils below male heads, involucral bracts connate, turbinate, enveloping cypsela, containing single female floret, corolla absent. Flowers: disc florets only, whitish; Apr. Fruit with cypsela ovoid, enveloped in turbinate, involucral bracts, with 4-6 spines on shoulders. Pappus absent.
Herbaceous perennial, stems simple, up to c. 1 m tall, arising from underground runners and so establishing large colonies. Leaves mostly opposite, bipinnatisect, the ultimate segments narrowly oblong, on average less than 2 mm broad, acute or acuminate, pubescent, light green, somewhat aromatic. Male heads small, drooping, in slender terminal racemes up to c. 12 cm long, paniculately arranged, female heads solitary or 2-3 together in the leaf axils below them.
Dry Grassland; Mesic Grassland. Weed of disturbed places.