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Plant Highlight: Peniocereus serpentinus

September 2016

Peniocereus serpentinus belongs to a group of Peniocereus which were formerly put in the genus Nyctocereus. Some taxonomists feel that the 2 groups should be kept separate, so it is sometimes listed as Nyctocereus serpentinus. It is native to southern Mexico, and is widely grown for its attractive fragrant flowers. Common names for this cactus include Night-Blooming Cereus and Queen of the Night, but these names are also applied to other cacti with large nocturnal flowers, such as Selenicereus grandiflorus.

The slender stems of Peniocereus serpentinus are cylindrical and up to 10 feet (3 m) long, and they put out offshoots at the base to form a cluster. Initially they are upright, but as they lengthen they sprawl to the side unless supported by surrounding vegetation. In cultivation, they may be attached to a trellis or fence for support. There are 10 to 17 ribs running down the length of each stem, with grooves between these. At close intervals along the ribs, there are clusters of needle-like spines. These are reddish-brown with darker tips initially, and they whiten with age.

Although Peniocereus serpentinus is night-blooming, the flowers remain open the following morning. The flowers are 6 to 8 inches long (15-20 cm) and about 3 inches across (8 cm). The lower part of the flower consists of a long tube, and this is spiny at the base (the part outside of the ovary), with the spines giving way to hairs above this, and then smooth at the upper part of the tube. The “petals” are referred to as tepals, because there is no clear line between the sepal-like outer ones, which are greenish with a red tinge, and the petal-like inner ones, which are white.

At the Ruth Bancroft Garden, this species flowers in the latter part of summer, with the fruits coming ripe primarily in August through October. The tasty round fruits are green at first, but turn bright red at maturity. They are about 1½ inches in diameter (4 cm) and are spiny on the outside, but the spines detach easily when the fruit is ripe.