The Beaucarnea-Calibanus clade

In my laboratory, we generally use dicotyledonous woody groups with conventional cambia as study systems. To offer a contrast to these groups, thus hopefully ensuring the generality of our work, we have selected groups with differing stem constructions. One such group is the clade (a group of related species) made up by the genera Beaucarnea and Calibanus, which are members of Ruscaceae. The 15 or so species of this group are mostly restricted to Mexico, and, like most of the groups we study, cover a remarkable range of sizes and shapes. All species of the Beaucarnea-Calibanus clade have bloated stem bases and long grassy leaves. However, the range in size and habitat is striking: some species are 15 meter tall trees of wet tropical forest, whereas some dryland species have no aerial stem, with the leaves springing directly from a giant globular stem below ground. Visit our people page to see who's working on this striking group.

Beaucarnea recurvata

This species is the most commonly cultivated member of the clade. It is a striking member of seasonally dry tropical forests of various parts of Mexico, mostly in the area of the Eastern Sierra Madre. Individuals of this species can reach more than 14 meters in circumference! This species can grow on vertical rock faces, as at left, or lend a surreal effect to dense woods on flat ground, as below. In many cases, the stems are covered with lichens, mosses, and epiphytic bromeliads and cacti, as at below right.

Beaucarnea recurvata in the wild Oaxacan populations of Beaucarnea recurvata tend to have especially thick trunks. The photos here are from a very dense tropical dry forest with very fat but short B. recurvata, the columnar cactus Neobuxbaumia scoparia and an understory of the terrestrial bromeliad Hechtia.
Beaucarnea recurvata in the wild The forest in this area is so dense that it is hard to take photos that do the plants justice. Rather than a clear view, it is more common to see the giant Beaucarneas as apparitions through tangles of branches. The individuals in this population are often 10 meters in circumference and about the same height! This image shows one large Beaucarnea at center and a smaller one at right.
Beaucarnea recurvata growin in the wild with Bursera A massive individual of Beaucarnea recurvata growing with Bursera ovalifolia and Neobuxbaumia scoparia with Hechtia in the foreground. This image was taken toward the end of the dry season. You can see the Hechtia leaves curled from the long drought and other plants leafing out in anticipation of the rains.
Beaucarnea recurvata in the wild A view of the incredibly dense and spectacularly varied forest that these plants grow in.
Beaucarnea recurvata in the wild Beaucarnea recurvata in the wild in Oaxaca, with Julieta for scale. You can get an idea of the size of the massive conical trunk of these plants, and of the relatively short branches of these individuals. The cactus at right is Neobuxbaumia scoparia.
Beaucarnea recurvata trunk The trunk of Beaucarnea recurvata is often swathed in epiphytes. This large individual had its trunk carpeted with the cactus Selenicereus testudo, along with agaves, orchids, bromeliads, and even a seedling of Plumeria.
Beaucarnea recurvata in the wild Because they are so avidly removed by collectors and nurserymen, it is very rare to find Beaucarnea populations that still have small individuals. This population is within a well protected patch of tropical dry forest and is remarkable for still having small plants. This image also shows the carpet of pink Hechtia that makes walking in these woods difficult .

Beaucarnea stricta

This species is smaller than B. recurvata, and grows in much drier tropical forest. It typically has a very thick base and several spindly branches with tufts of bluish leaves. Fairly large individuals are shown in the two photos at left. The branches may die back to the base, leading to strange-looking individuals such as the one being sampled by Alan and Jessica, below. Like many Beaucarneas, this species often grows on steep hillsides, in this case with massive columnar cacti and groves of huge cycads.

Beaucarnea gracilis

Endemic to the Valley of Tehuacán, this species has bark that would look at home on a pine tree. This species grows in dry tropical scrub and has very narrow, stiff bluish leaves. One study suggests that Beaucarnea gracilis is having a hard time in the wild, since too many people are digging up the small plants to use them as ornamentals: Cardel, V. 1997. Ecological status of Beaucarnea gracilis, an endemic species of the semiarid Tehuacan Valley, Mexico. Conservation Biology 11 (2): 367-374.

Beaucarnea purpusii

As is the above species, B. purpusii is restricted in its distribution to a few relatively high dry tropical localities. It is remarkable for being highly branched, often with many stout trunks and a relatively slender base. The leaves of this species are broader than those of B. stricta, which grows nearby, and can accumulate along the branches in very dense, long-lived mats. Like the other dryland species of the clade, the bark of B. purpusii  is very thick and furrowed.


Beaucarnea goldmanii

This species grows in dense woods, where its tall, slender stems poke above the canopy in rocky areas. The individual shown at left was growing on an exposed rock face in dense scrub on the walls of the Sumidero Canyon in Chiapas. In contrast to many other members of the clade, the leaves of B. goldmanii have relatively few adaptations for dealing with drought. The dense grove of B. goldmanii in the photos below is from the dry central depression of Chiapas.
Beaucarnea goldmanii base
Beaucarnea goldmanii   Beaucarnea goldmanii   Beaucarnea goldmanii
Beaucarnea goldmanii in the wild in Chiapas This population of Beaucarnia goldmanii was growing in dense dry tropical forest on a steep limestone slope. The plants were much smaller than in the grove shown above.

Beaucarnea hiriartae

This species was described in the early 90s, despite growing in an area that is relatively well known floristically. That remarkable novelties continue to come to light in Mexico is illustrative of the richness of its flora. This species grows on very hot, rocky hillsides in lowland dry tropical forest of the interior of Mexico. It is a relativaly small species, and has much thinner bark than most of the other species. On relatively deep soil, it may reach heights of 5-6 meters, but on exposed rock, the plants may be half that height.

Beaucarnea compacta

The smallest member of the genus, this species usually has its leaves in sessile or nearly sessile rosettes springing directly from a large globular basal stem. In some cases, as in the two images at left, leaf rosettes are borne on short stems; the individual at lower right had the longest stems that we have encountered. The three photos below show various aspects of a large plant in fruit. Note the long, pendant flower stalk and the way the leaves cover the stem in a dense mat.

Calibanus hookeri

Uncharitably named for the monster in Shakespeare's The Tempest, this species is widespread in the tropical southern extensions of the Chihuahuan Desert. Like the above species, Calibanus hookeri has a large, globular stem with rosettes of slender, stiff bluish leaves scattered directly over its corrugated surface. In C. hookeri, the stem is largely below ground. The above ground parts of the stem are usually protected beneath a dense thatch of leaves. It often grows with cacti, as at lower left, or with the bromeliad Hechtia, below. This clade forms part of the thesis project of Vanessa Rojas, below right.


Calibanus glassianus

The other species known from the genus Calibanus, C. glassianus differs conspicuously from C. hookeri in its stem, which is largely above ground. The bark of C. glassianus varies from large plates to small protruberances. Like C. hookeri, the rosettes of leaves of this species almost always emerge directly from the surface of the globular stem, without any elongated trunks.  Perhaps the  most striking thing about this species is its incredibly close resemblance to B. compacta. Ongoing phylogenetic studies will reveal valuable information regarding the relationships within this remarkably varied clade.


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