Arrow poison plant, hierba de la fleche Arrow poison plant, hierba de la fleche

Sebastiania bilocularis S. Watson, Proc. Amer. Acad. Arts 20: 374. 1885; Sapium biloculare (S. Watson) Pax; S. biloculare var. amplum I. M. Johnston

Shrubs or small trees, 1–8 m. Leaves distichous, clustered at branch tips; stipules triangular, 0.8–1 × 1.5–2.5 mm, erose, hyaline; petiole 1.2–4 mm, glands 0–2, orbicular, axil with tuft of coarse glandular hairs; blade lanceolate, 2–7 × 0.5–1.8[–3] cm, base acute, margins with fine teeth bearing setae, teeth sometimes replaced by orbicular glands, apex acute. Inflorescences: peduncle 0.2–0.6 cm; fertile portion 3–6 cm; staminate cymules numerous, condensed, each with 3–10 flowers per bract; pistillate flowers 0–4 per inflorescence, 1 flower per bract; bracts ovate, 1.5–2 mm, subtended on each side by row or cluster of 5–7 elliptic glands, 0.1–0.3 mm diam. Pedicels 0–2 mm. Staminate flowers yellowish green; sepals 0.5 mm; filaments 0.3–0.8 mm, anthers 0.2–0.3 mm. Pistillate flowers yellowish green; sepals ovate, 1–2 mm; styles 2.5–3.5 mm, connate 1/3 length, free portion coiled. Capsules subglobose, 0.5–-1 cm diam. Seeds 4–5 mm, wider than long; seed coat silver and brown mottled, smooth with verrucose patches. 2n = 22.

Flowering and fruiting year-round. Sonoran desert scrub, thorn scrub; 0–1000 m; Ariz.; Mexico (Baja California Sur, Sonora).

Pleradenophora bilocularis reaches its northern limit of distribution in southwestern Arizona and is widespread in adjacent Sonora, Mexico. Across its range, there is a six-fold variation in leaf width with collections from Baja California being much wider (to 3 cm) and formerly recognized as a distinct variety (V. W. Steinmann and R. S. Felger 1997). The species is a minor source for “Mexican jumping beans” from seeds parasitized by moth larvae. Indigenous populations used the latex as arrow and fish poison (C. E. Bradley 1956).