Cleistocacti are mostly columnar cacti from several South American countries, though one or two species do have a sprawling habit. Several of them will produce their hummingbird pollinated, tube-like flowers when still quite small, though C. strausii needs to get to maybe 600mm (2 feet) tall before it will oblige. Its silvery spined stems branch from the base and then grow straight upwards towards the greenhouse roof, making a pleasant backdrop for the more numerous globular cacti.
The picture was taken at the Desert Museum, Tucson Arizona, but the plant grows easily under glass in the UK.

 
Photograph by : John Ellis