3. Ambrosia psilostachya Candolle, Prodr. 5: 526. 1836.
裸穗豚草 luo sui tun cao
Ambrosia coronopifolia Torrey & A. Gray.
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.
Recently naturalized in Taiwan [native to temperate North America and parts of South America].
The occurrence of this species in Taiwan was first reported by Y. H. Tseng and C. I Peng (Endemic Sp. Res. 6: 71-74. 2004).