豚草 tun cao

Ambrosia artemisiifolia var. elatior (Linnaeus) Descourtilz; A. elatior Linnaeus.

Annuals, 20-150 cm. Stems erect. Leaves opposite and alternate; petiole 2.5-3.5(-6) cm; blade deltate to lanceolate or elliptic, 2.5-5.5(-9) × 2-3(-5) cm, pinnately 1- or 2-lobed, abaxially sparsely pilosulose to strigillose, adaxially strigillose, both surfaces gland-dotted, base cuneate, ultimate margin entire or toothed. Female capitula clustered, proximal to male; floret 1. Male capitula: peduncles 0.5-1.5 mm; involucres shallowly cup-shaped (usually without black veins), 2-3 mm in diam., glabrous or hispid to pilosulose; florets 12-20. Burs ± globose to pyriform, 2-3 mm, ± pilosulose, spines or tubercles 3-5, near middle or apex, conical to acerose, 0.1-0.5 mm, tips straight. Fl. Jul-Oct, fr. Sep-Oct. 2n = 34, 36.

Introduced noxious weed of wet to dry soils; below 1000 m. Widely distributed in China [native to Central and North America; introduced and widely distributed in Asia and Europe].