^{(Photograph: Cleistocactus smaragdiflorus flower, Peter A Mansfeld)}

Introduction

Cleistocactus means “closed” or “hidden” cactus. The flowers are narrow and barely open in some species, hence they are closed (the interior of the flower is hidden). Cleistocactus species are found in Argentina, Bolivia, Ecuador, and Peru where some species grow at 2,000 m or higher (over a mile in altitude).

The Details

It is not clear how many species there are in the genus because some authors lump a lot of plants (e.g., Hildewintera, Borizicactus, Seticereus, and more) into Cleistocactus. Other authors keep these genera separate.

The typical Cleistocactus plant has few to many upright stems that can be several-feet tall. The stems are 1-2 inches in diameter. Flowers can be red, orange, or even greenish depending upon the species.

There are two special things about Cleistocactus species. The flowers are hummingbird pollinated. Hummingbirds are just perfect for the narrow (almost tubular) flowers that are open during the day.

The second thing is that Cleistocactus species have a cephalium. A cephalium is a specialized area on the plant with bristly, woolly, or woody growth where flowering occurs. Flowers are only produced in the cephalium. In Cleistocactus, the cephalium is on the side of stem, near the top.

Additional Information: Flower Density on Cleistocactus