What is "cleistocactus"

Cleistocactus is a genus of columnar cacti native to mountainous areas - to - of Peru, Uruguay, Bolivia and Argentina. The name comes from the Greek kleistos meaning closed because the flowers hardly open.

The stems are tall and mostly slender and often many-branched with numerous ribs with closely set areoles and spines. The flowers are tubular and the tips hardly open with only the style and stamens usually protruding.