Discocactus placentiformis
Discocactus placentiformis is a species of flowering plant in the family Cactaceae. It is found in Brazil.
Description
Discocactus placentiformis is a small, solitary cactus characterized by its depressed, globular stem, which can reach 3.5 to 13.4 cm in height and 6 to 29 cm in diameter. Its epidermis is dark green and it possesses branched roots. The stem features 9 to 26 distinct ribs, arranged vertically or slightly spirally, divided into tubercles with shallow grooves between areoles. These oval to elongated, sunken areoles, measuring 0.3 to 1.5 cm long and 0.2 to 1.2 cm wide, are located above ground and there are typically 3 to 9 per rib. Spines are gray to brown and flattened or rounded in cross-section, consisting of a single central spine, sometimes absent, that is 0.9 to 2 cm long and 1 mm in diameter, along with 3 to 10 radial spines ranging from 0.5 to 4.5 cm long and 1 to 4 mm in diameter.Adult plants develop a woolly cephalium at their apex, measuring 0.5 to 7 cm high and 1 to 11 cm in diameter. This sometimes depressed structure, composed of white wool and dark bristles on its margin, protects the plant's sensitive tip from cold and intense UV radiation and is thought to attract pollinators due to its showy appearance even before flowering. The flowers, which emerge from the cephalium's edge, are white, fragrant, and funnel-shaped, opening at night and attracting moths. They can be solitary or in clusters of 2 to 16, reaching up to 8.5 cm in length and 7.5 to 8.5 cm in diameter. The ovoid pericarpel, 5 to 7 mm long and 4 to 6 mm wide, varies in color from white and reddish-brown to pink. The slender floral tube, 3.4 to 5 cm long and 0.7 to 1.2 cm wide, has fleshy, olive to brown scales. Inner perianth segments are 1.5 to 3 cm long and white, while outer segments are 1.8 to 3.5 cm long and greenish-white. Stamens have 4 to 5 mm long filaments and 0.75 to 2 mm long yellow anthers. The style is 3 to 4.5 cm long and the stigma has 4 to 8 cream to white lobes, enclosing ovules arranged in clusters of 1 to 5.
The fruits are club-shaped, white to reddish at the apex, and measure 3 to 5 cm long and 0.5 to 1.5 cm wide. They split longitudinally when ripe and retain persistent floral remnants. Inside, they contain shiny, oval, black seeds measuring 1.2 to 1.9 mm long and 1 to 2 mm wide, with a testa covered in irregularly distributed nipple-shaped tubercles.