Brachycereus nesioticus aka Lava Cactus

Brachycereus nesioticus, or lava cactus, belongs to the cactus family. It is native to the Galápagos Islands of Ecuador. Its range includes Bartolomé, Fernandina, Genovesa, Isabela, Pinta, and Santiago. It lives on dry lava fields near sea level. Roots take hold in cracks where little soil exists. This cactus is among the first plants to settle new lava. Dead stems break down and add humus around the clumps.

This slow-growing succulent forms dense groups of short, columnar stems. Clumps reach about 2 feet [0.6 metres] tall. They can spread to 6.6 feet [2 metres] wide. Individual stems stand upright or lie along the ground. They reach 0.3–1.6 feet [0.1–0.5 metres] long. Each stem has 14–22 ribs beneath a thick spine cover. The many spines give the plant a furry look. Some are stiff, while others bend a little. Young growth looks yellow, then turns brown or black. Older growth takes on a grey tone.

Creamy white flowers grow from the sides of the stems. Each has a narrow funnel shape and a long tube. Small scales and spiny areoles cover the flower tube. The flowers open just before dawn. Most fade by seven or eight in the morning. The fruit turns tan and fleshy as it ripens. Yellow spines cover it, and old flower parts remain attached. Inside are small, dark brown to black seeds. Their shape ranges from round to oval.

In cultivation, this cactus needs rich soil that drains freely. Give it some shelter from strong sun. Water during active growth, but stop when it becomes dormant. Keep it on the dry side through winter. LLIFLE advises winter greenhouse temperatures above 12°C. It also warns against temperatures below 5°C. Its dry native habitat does not mean it needs no water. It can take more water while making new growth.

This species remains rare in cultivation and is hard to propagate. Seeds and plants are difficult to obtain. Cuttings seldom form roots and survive. Grafting has proved the main successful way to raise it. Ecuador bans plant collection in the Galápagos national park. Its wide clumps help establish plant life on bare lava. The supplied sources give no details on garden pests or diseases. They also provide no evidence of food uses or toxicity.