Discocactus hartmannii

Discocactus hartmannii is a small, solitary cactus with a disc- or globular shape. It measures 4–7 cm in height and 7–19 cm in diameter, featuring dark green epidermis and branched roots. The plant has 14–22 spiral ribs with deep grooves (>2 cm) between areoles, arranged in a spiral and divided into elongated, conical tubercles supported by 3–7 oval to elongated areoles (2–6 mm long, 1.75–4 mm wide). Areoles appear sunken. Spines start yellowish to horn-colored, turning gray-brown with age. They are curved, rounded in cross-section, with a single central spine (sometimes absent) 0.1–0.8 cm long, and 3–12 radial spines measuring 0.2–2 cm. At the apex of mature plants, a woolly cephalium (1.3–3.5 cm high, 2.7–6 cm diameter) forms, composed of white wool with bright to dark bristles (0.2–4 cm). It protects the apex from cold and UV radiation and attracts pollinators. The white, fragrant, tubular flowers emerge at the cephalium's edge, opening at night and pollinated by moths. They are 7–7.6 cm long and 4.2–5.5 cm in diameter, with light brown to olive-green buds. The floral tube is 4.5–5.8 cm long, with white to light olive-green scales inside and outside. Inner perianth segments are 2.3–2.6 cm long; outer segments are 2.2–2.8 cm. Stamens have filaments 0.4–1.1 cm long with yellow anthers (1–2 mm). The style is 3.7–5.1 cm long, with a stigma of 5–8 lobes. …

The native range of Discocactus hartmannii species extends from Amambay, Concepción, San Pedro, and Canindeyú departments in Paraguay to west-central Brazil specifically in the states of Goiás and Mato Grosso do Sul and grows primarily in the seasonally dry tropical biome. Plants grow in sandy grassland soils and stony hills composed of silt, sand, gravel, or rocky soil with a high concentration of mica, at elevations of 280 to 700 meters above sea level.