Sauropus quadrangularis (Willdenow) Müller Argoviensis

Sauropus quadrangularis has distinctive ovaries and fruits, longer than wide and with usually erect stigmas inserted in an apical depression delineated by a distinct rim. Varieties based on variation in stem morphology, whether the branchlets are 4-angled or compressed and only 2-angled (var. compressus), and in indumentum (var. pubescens), are not well-founded as these characters can vary within populations.

Erect shrubs to 1 m tall, monoecious, glabrous [to hirsute] throughout; stem gray-brown; branchlets 4-angled or compressed. Stipules lanceolate [to sometimes strongly falcate], 1-2[-2.7] × 0.7-1.2[-3.5 when falcate] mm; petiole 1-1.3 mm; leaf blade ovate, elliptic, or rounded, 5-20(-25) × 3-12 mm, membranous or thinly papery, base rounded or obtuse, apex rounded or obtuse, mucronate; venation pinnate, lateral veins 4 or 5 pairs, slender, obliquely ascending, not raised. Inflorescence subtended by leaves, 1- or 2-flowered. Male flowers 2-3 mm; calyx discoid, ca. 1.5 mm in diam., 6-lobed; sepals apex obtuse or retuse; disk scales very short; anthers spreading. Female flowers: pedicels 2.3-4.3 mm; sepals subobovate, apex acute; disk 6-lobed; ovary small, apex concave, with crenulate rim; stigmas erect. Capsules ovoid, 5-5.5 × ca. 4 mm, rather woody when dry, with lobed rim around stigmas, exocarp thin, spreading, ± stellate when dry. Seeds 3-angled, ca. 3.5 × 2 × 2 mm. Fl. Jun-Oct, fr. Sep-Dec.

Guangxi, Xizang, Yunnan [Bhutan, Cambodia, India, Laos, Myanmar, Nepal, Thailand, Vietnam].

Open forests or valley scrub, broad-leaved forests; 100-2100 m.

Phyllanthus quadrangularis Willdenow, Sp. Pl. 4: 585. 1805; Aalius ceratogynum Kuntze; A. compressa (Müller Argoviensis) Kuntze; A. pubescens (J. D. Hooker) Kuntze; A. quadrangularis (Müller Argoviensis) Kuntze; A. rigida (Thwaites) Kuntze; Ceratogynum rhamnoides Wight; P. leschenaultii Müller Argoviensis var. tenellus Müller Argoviensis; P. rhamnoides Roxburgh (1832), not Retzius (1788); Sauropus ceratogynum Baillon; S. compressus Müller Argoviensis; S. concinnus Collett & Hemsley; S. pubescens J. D. Hooker; S. quadrangularis Müller Argoviensis var. compressus (Müller Argoviensis) Airy Shaw; S. rigidus Thwaites.

Rau ngót vuông (danh pháp khoa học: Sauropus quadrangularis) là một loài thực vật có hoa trong họ Diệp hạ châu. Loài này được (Willd.) Müll.Arg. miêu tả khoa học đầu tiên năm 1863.

方枝守宫木（学名：Sauropus quadrangularis）为大戟科守宫木属下的一个种。