Flowering from April to June; fruiting from May to August.
Geranium robertianum is occurring in Guizhou, Hubei, Hunan, Sichuan, Taiwan, Xizang, Yunnan, Zhejiang of China, Japan, Kazakhstan, Korea, Kyrgyzstan, Nepal, Pakistan, Russia, Tajikistan, Turkmenistan, Uzbekistan; Africa, W Asia, Europe.
Biennials or sometimes annuals. Stem 10-55 cm tall, erect, not rooting at nodes, with patent glandular trichomes. Stipules ovate, distinct. Leaves opposite; petiole with retrorse not appressed nonglandular trichomes and patent glandular trichomes; leaf blade 3-9 cm long, palmately divided, pilose with glandular trichomes; segments 5, rhombic, with a petiolule on middle segment, 16-40-lobed in distal half. Cymules solitary, 2-flowered; peduncle 1-6 cm long. Pedicel 0.5-2 cm long; bracteoles lanceolate. Sepals 6-8 mm long, mucro 1.8-2.5 mm, outside with 0.3-0.5 mm ± patent nonglandular trichomes and 0.4-3.2 mm patent glandular trichomes, inside glabrous. Petals purplish, 7.5-10 mm long, erect to patent, glabrous, apex rounded. Staminal filaments pinkish, lanceolate with an abruptly narrowed apex, glabrous; anthers purplish, 0.4-0.6 mm long. Nectaries 5, hemispheric, glabrous. Stigma pinkish. Fruit 1.9-2.5 cm long, erect when immature; mericarps reticulate, ridges sparse and scarcely anastomosing in basal half but denser apically and forming 1-2-overlapping collar-like keels at apex, without a basal callus, glabrous or sometimes with nonglandular trichomes, small glands, or both; rostrum 1.7-1.9 cm long, with a 4-5 mm narrowed apex; stigmatic remains 1-1.3 mm. Seeds 2.1-2.2 mm.
The chromosomal number of Geranium robertianum is 2n = 64 (Arohonka, 1982; Laane and Lie, 1985; Lövkvist and Hultgård, 1999).
Growing in forest; 1000-3500 m.
