Eye-catching Calibanus is easy to grow
There are not many plants with Shakespearean names, but we have an unusual one at the Ruth Bancroft Garden — Calibanus hookeri, named after the character Caliban in Shakespeare’s play “The Tempest.” In the play, the character is grotesque, and apparently it was the plant’s swollen base and craggy surface that led to the name.
Calibanus hookeri is native to east-central Mexico, where it grows on rocky hillsides along with various kinds of cactus and dry-growing shrubs. Its blue-green leaves are wiry and grass-like, arising in tufts from the dome-like base. Growing up to a foot long, they remain on the plant throughout the year. The base starts out as a little lump, but on old plants it can grow to be as much as two to three feet across, with corky bark and deep fissures.
Often, these plants grow wedged between rocks, and they can be hard to spot because the impression is of grasses growing among boulders. On closer inspection, some of the rocks are not rocks at all, and the grasses are clumps of leaves emerging from them.
Calibanus hookeri is summer-blooming, with short branched flower stalks arising among the leaves. Rather than growing straight up, the stalks arch to the side, and the branches bear many tiny white flowers. Any given plant is either a male or a female; the males can be recognized by their stamens tipped with yellow pollen. The females lack pollen, but they alone are capable of producing seeds, provided they are pollinated successfully by visiting insects. The reddish fruits are round or oval and about the size of a marble. They stand out among the blue-green leaves, and are much showier than the small flowers, which can easily be overlooked.
Although Calibanus hookeri is an unusual plant with a unique appearance, it does have a more commonly-grown close relative, the ponytail palm. This latter plant is named Beaucarnea recurvata, and it is not really a palm at all. In Beaucarnea, the seeds are held in a papery capsule with three wings, rather than in a berry-like fruit, as in Calibanus.
More conspicuously, the shoots of the ponytail palm do not remain as just little tufts coming out of the large base, as they do in Calibanus. Instead, they elongate to form tall branching trunks, each with a clump of leaves at the end. A mature Beaucarnea can reach over 20 feet in height, with a base as big as a VW beetle.
Despite these differences, the two are so closely related that it is possible to hybridize between them. As might be expected, the hybrid is intermediate between the two parents. The shoots elongate, but not so much as to become tree-like.
In the garden, both Calibanus and its hybrid are easy to grow, needing only excellent drainage and occasional water during their growing season in the summer months. The combination of the large woody base and the grassy foliage makes them wonderful focal points and conversation pieces.