Origin and Habitat: Melocactus deinacanthusSN|2270]]SN|2270]] is a rare and isolated species, endemic to east of the Rio Sao Francisco in southern Bahia (Brasil)
Altitude. 500–540 m.
Habitat: Grows on large plates of exposed granite/gneiss rock often in large numbers with several rare plants in crests form. It is a co-dominant element of the rupicolous vegetation. The 2 only population known are seriously threatened by agriculture development and by inundation from the “represa de spradinho” a large dam lake on Rio São Francisco.

• Melocactus deinacanthus Buining & Bredero

• Melocactus ernestii Vaupel
• Melocactus oreas subs. ernestii (Vaupel) P.J.Braun
• Melocactus azulensis Buining & Bredero
• Melocactus oreas f. azulensis (Buining et al.) P.J.Braun
• Melocactus deinacanthus Buining & Bredero
• Melocactus diamantinus hort.
• Melocactus sp. Mercedes de Diamantina, Minas Gerais, Brazil
• Melocactus ernestii var. multiceps hort.
• Melocactus azulensis f. multiceps
• Melocactus multiceps
• Melocactus oreas f. multiceps
• Melocactus erythracanthus Buining & Bredero
• Melocactus oreas f. erythracanthus (Buining & Bredero) P.J.Braun
• Melocactus interpositus F.Ritter
• Melocactus longispinus Buining & Bredero
• Melocactus oreas var. longispinus (Buining & Bredero) P.J.Braun
• Melocactus nitidus F.Ritter

• Melocactus ernestii subs. longicarpus (Buining & Bredero) N.P.Taylor
• Melocactus deinacanthus subs. longicarpus (Buining & Bredero) P.J.Braun
• Melocactus longicarpus Buining & Bredero
• Melocactus florschuetzianus Buining & Bredero
• Melocactus deinacanthus subs. florschuetzianus (Buining & Bredero) P.J.Braun
• Melocactus deinacanthus var. florschuetzianus (Buining & Bredero) P.J.Braun
• Melocactus montanus F.Ritter
• Melocactus mulequensis Buining & Bredero
• Melocactus deinacanthus f. mulequensis (Buining & Bredero) P.J.Braun
• Melocactus neomontanus Van Heek & Hovens

Description: It is a large species strictly related to Melocactus ernestiiSN|2270]]SN|2264]]
Stem:Usually solitary, globose to cylindrical about 35 cm tall and 25 cm in diameter.
Ribs: 10 to 12 sharp-edged.
Cephalium: Up to 25 cm tall and 9 cm in diameter. In contrast to the typical cephaliums covered with reddish bristles, in Melocactus deinacanthusSN|2264]]SN|2270]], the upper portion of the cephalium tends to remain white, with few bristles to poke out beyond an abundant layer of woolly fibers. The immature plant looks like a smallish barrel cactus, and there is nothing in its appearance that would suggest a Melocactus.
Central spines: 4-7 reddish-brown up to 5,3 cm long.
Radial spines: 11-14 slightly curved up to 8 centimetres long.
Flowers: Up to 2,6 cm long and 1,2 cm in diameter in various gradation of pink-magenta
Fruit: Club-shaped pure white 1,2 to 2,2 centimetres long.

Notes: The most remarkable part of a Melocactus is its cephalium a bristle-coated structure on the summit of the plant, only Melocactus, and the similar genus Discocactus possesses this type of permanent, apical, hatlike appendage. It’s only when a Melocactus reaches maturity that the cephalium begins to grow. Cylindrical, with a diameter distinctly smaller than that of the plant body below, the cephalium will keep growing for the rest of the plant’s life, but the body of the plant stops growing the moment the cephalium starts to form. As the plants age the cephalium doesn’t increase in circumference it will steadily grow taller

Cultivation and Propagation: These cacti are not the easiest things to grow and aren’t plants for beginners. Melocactus deinacanthus grows from April to October, it can’t endure long stretches of total dryness, and also too much water will rot it, as its weak root systems tends to be inefficient at sucking up water from wet soil. Nonetheless, again as a result of their tropical origins, they need a fair amount of water, but allow the soil to dry quite a bit before watering again. Melocactus rests from October to April but can’t stand cold, or even fairly cool temperatures, so is indispensable to keep it above 8-12°C at all times, severe damage or death occurring at temperatures that the great majority of cacti wouldn’t mind in the least and prefer more frequent water in winter than other cacti, say once a month. Do not feed in winter.
The root system is weak and generally resents being repotted and can take a long time to re-establish. The soil mix should be very quick draining, prefers very bright light, not as much as the most arid growing cacti, but plenty nonetheless.
Propagation: Exclusively by Seeds. Sow in February-march in a light, sandy, porous soil. Cover germinating tray with glass to prevent seed from drying out. Germination is most successful at a temperature of 18 to 22° C.