Cereus spegazzinii aka Moonlight Cactus

Cereus spegazzinii is a slim cactus with stems that branch. It belongs to the cactus family, Cactaceae. It also goes by the name Monvillea spegazzinii. People call it moonlight cactus and nightblooming cereus. It is native to Bolivia, Brazil, Paraguay, and northern Argentina. Kew places it in the tropics, where seasons bring dry spells. It grows in dry forests and at their edges. LLIFLE lists several provinces in northern Argentina where it grows. These include Chaco and Salta.

This succulent shrub grows many shoots from its base. The shoots form a clump as the plant grows. Its stems may stand up or lie in part along the ground. They reach about 5.9 feet [1.8 metres] long, sometimes more. This is their length, not a fixed height above ground. The stems branch and have patches of blue, green, and purple. Its fleshy roots have a tuber-like form. Roots that grow away from the main root system become fleshy too.

Each stem has three to five angular ribs, most often four. Deep notches break the edges of these raised ribs. Small areoles, which bear spines, sit on the raised tips. Young growth tends to have three sharp, dark spines per areole. Two point up, and the third points down. Older stem parts have five radial spines around one central spine. The longer spines reach about 0.05 feet [0.015 metres]. These traits help tell young shoots from older stem growth.

Flowers open in the early evening and bloom at night. LLIFLE lists April to September as the bloom season. Each flower is about 0.33–0.43 feet [0.10–0.13 metres] long. A thin tube holds the perianth segments, or flower parts. The outer parts are reddish; the inner ones are white. Flowers grow on the stem sides near their tips. Buds point up, then bend down as they open. The fruit has smooth red skin and juicy flesh. Wilted flower parts stay on its tip as they dry.

The flowers and patchy stem colors give the plant its garden appeal. LLIFLE says it is still widespread and common. In some places, it grows in large numbers. LLIFLE gives it a Least Concern conservation status. It notes no major threats and groups in protected areas. The supplied species evidence does not state its growing needs or cold limits. It confirms no food use and gives no toxicity assessment. Nor does it name any specific pest problems.