Obregonia denegrii aka Artichoke Cactus

Obregonia denegrii, or artichoke cactus, belongs to the cactus family. It is the sole species in its genus. Kew lists its native range as Nuevo León and Tamaulipas, Mexico. LLIFLE describes a small range near Jaumave in Tamaulipas. It grows in dry shrubland, on lower slopes among limestone gravel. Plants live in open ground and beneath dense shrubs. Rain can wash them from slopes where soil erodes.

This cactus forms a single, low stem near ground level. It reaches about 0.5 feet [0.15 metres] across, sometimes more. The stem ranges from grey-green to dark green. Its shape recalls an artichoke or an upside-down pine cone. A thick taproot anchors it below ground. Triangular tubercles form a spiral around a sunken, woolly centre. These leaf-like bumps have flat tops and ridged undersides. Small areoles sit at their tips and bear wool when young. Young tubercles carry two to four pale or brown spines. These bend with ease, curve slightly, and often fall off soon.

White, funnel-shaped flowers open by day during summer. They rise through the wool at the stem's centre. Blooms reach about 0.08 feet [0.025 metres] across. Their length reaches about 0.10 feet [0.03 metres]. The outer flower parts have a grey tint. Pink or purple-red filaments hold yellow anthers. White, pear-shaped fruits remain tucked within the wool. Their flesh is edible, and the fruits dry as they mature. Old flower remains stay attached. The seeds are black.

Growth is slow, and cultivation calls for care. Use a mineral mix that drains freely, with little organic matter. Light sun helps the stem keep its compact shape. Water sparingly from March through October. Keep it dry in winter, or when nights stay below 10°C. Too much water can produce an elongated, less natural shape. Plants can grow on their own roots or as grafts. Seed is the main means of propagation. Tiny seedlings need careful watering and grow slowly at first. Plants may take seven to eight years to reach flowering size.

Growers raise this species as an ornamental for its sculpted stem. Wild plants face pressure from illegal collecting and livestock grazing. Local people also gather it for use against rheumatism. This records a traditional use, not proof that it works. These pressures affect a cactus with a small wild range.