Aloe pillansii (Bastard quiver tree)

aloe-pillansii-on-cornells-kop
An Aloe pillansii on Cornell’s Kop in Richtersveld National Park. Image from http://www.u4ba.nl.

It is an unlikely place to be found within a biodiversity hotspot: a dry, desolate wilderness where temperatures can reach upwards of 50 degrees Celsius (120 degrees Fahrenheit) and flora and fauna must survive on the moisture of the fog that sweeps in early each morning from the cold waters of the Atlantic Ocean. Nonetheless, the Richtersveld National Park region of Namaqualand in southern Namibia and the Northern Cape province of South Africa is part of the Succulent Karoo, the most biologically diverse arid region in the world, and the home of approximately one-third of the planet’s 10,000 succulent plant species.

succulent-karoo
The Succulent Karoo of the west and the Nama Karoo of the east.

“The flora of Southern Africa is extremely remarkable, not merely for the number of its species and their generally very restricted range, but also for the frequent singularity of their aspect and manner of growth. In each of these particulars the genus Aloe is no exception to the general rule,” wrote Sir William Turner Thiselton-Dyer, future director of the Royal Botanic Gardens, Kew, in “The Tree-Aloes of South Africa” in the journal Nature in 1874.

A more contemporary description of the landscape and its tree aloes is given in Wild Flowers of South Africa by Colin Paterson-Jones and John Manning. “A lunar landscape of forbidding mountains and arid plains blasted by both sun and wind marks the northern limits of Namaqualand. Here, the austere beauty is barely softened by a sparse covering of plants adapted to survive in this harsh land of searing summers and scant winter rain. Yet this forbidding country harbours the richest diversity of succulents in the world, dominated by the gaunt silhouettes of giant tree aloes.”

Despite the visual prominence of these gaunt silhouettes, there are actually very few trees endemic to the Succulent Karoo region—three, to be precise, and one of them isn’t really a tree.

Pachypodium namaquanum Halfmens
The Pachypodium namaquanum, or Halfmens. Photo © Martin Heigan (http://www.flickr.com/photos/martin_heigan)

The half-tree is a half-man, or so its name and local Khoisan legend would have it. The Pachypodium namaquanum, or Halfmens (Afrikaans for human-like or half-human), is a tree-like stem succulent whose vaguely human form is said to be the consequence of the Khoisan people’s yearning for their homeland. Driven from the Kalahari by invading tribes, some of them turned for a final glance at their birthplace and were transformed into the northward-leaning halfmens.

The two succulent species endemic to the Karoo that are actually trees are the Aloe dichotoma (Common quiver tree) and the Aloe pillansii (Bastard quiver tree). Though they’re found within the same area, they were “discovered” more than 150 years apart—a sign of how difficult the Karoo could be to botanize.

A. dichotoma and A. pillansii are visually similar, but A. pillansii can be distinguished by its drooping yellow flower spikes (A. dichotoma’s grow upwards) and white thorns (A. dichotoma’s thorns are yellow). A. pillansii also has larger leaves and fewer, thicker, and more erect branches.

In her book The Plant Hunters, Alice M. Coats states that A. dichotoma was discovered in November 1774 by Francis Masson (the Kew Gardens’ first plant hunter) and Carl Peter Thunberg (one of Carolus Linnaeus’ collectors, and an important figure in the history of Japanese botany). Unfortunately, the pair missed the main flowering season by two months. While in the Karoo, Coats writes, “they found [a] ‘great treasure’ of new succulents, but dared not stop to botanize; to save the lives of their oxen they were obliged to press on to the next water, nearly three days’ journey away.”

A. pillansii was not collected until over 150 years later, when the South African botanist Neville Stuart Pillans found it on Cornell’s Kop in Richtersveld in Little Namaqualand, the southern/South African portion of Namaqualand, in October 1926. Pillans’ name was given to the tree aloe two years later by Louise Guthrie, but unfortunately for Pillans’ memory this taxonomic name is joined to a common name that is a real attention-getter.

aloe-pillansii-in-richtersveld
An Aloe pillansii in the Richtersveld. Photo by Alberto Ballerio (http://www.pbase.com/philharmostes).

The name “bastard quiver tree” suggests all kinds of colorful etymological possibilities, but its definition is actually a sort of portmanteau referring to the tree’s location and usage. The tree aloes of the Succulent Karoo are also commonly known as Kokerboom trees. Kokerboom is Afrikaans for quiver (as in arrow quivers, not shaking and trembling). The Khoisan Bushmen would hollow out the interior of the tree’s soft branches, seal one end, attach a strap, and use them to carry their arrows.

The “bastard” portion of the name is likely a remnant of Southern Africa’s legacy of racism. A. pillansii could be found in the Richtersveld region that was one of the Baster states of South Africa, lands that were populated by the biracial descendants of white colonists and indigenous Khoi. There are still some 35,000 Basters remaining in South Africa today. The website http://rehobothbasters.org is dedicated to their history and current legal status.

Succulents are uniquely suited to surviving in the hostile environment of the Richtersveld. For example, the waxy surface of their leaves helps them to retain water, and they’re more efficient photosynthesizers than other plants. Yet the challenges to survival that A. pillansii faces are formidable, and its place in the region has become highly precarious. It’s one of the world’s most endangered plants, and is protected by law in South Africa and included in Appendix 1 of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). It’s also on the International Union for Conservation of Nature (IUCN) Red List of Threatened Species.

bastard-quiver-tree
A young Aloe pillansii. Photo by Alberto Ballerio (http://www.pbase.com/philharmostes).

In 1997, the journal Biodiversity and Conservation published an article entitled “Population ecology of tree succulents (Aloe and Pachypodium) in the arid western Cape: decline of keystone species” by J.J. Midgley, R.M. Cowling, H. Hendricks, P.G. Desmet, K. Esler, and P. Rundel. In it, Midgley et al. examined the ongoing population decline of A. dichotoma, A. pillansii, and P. namaquanum (aka halfmens).

“In the Richtersveld,” Midgley et al. wrote, “all three species have very few [seed] recruits and both Aloe species have a high incidence of mortality especially of large individuals… This is especially serious for A. pillansii because it is endemic to a small area…” In fact, A. pillansii is “near endemic” to the Richtersveld Community Conservancy, particularly Cornell’s Kop, according to the Conservancy’s website (http://www.richtersveld-conservancy.org).

Midgley et al. cited “excessive, but localized, herbivory by baboons and porcupines,” who gnaw the stems of the trees, as a leading cause of their endangerment. Theft by plant collectors was also cited by a 2006 Vegetatio article as a probable cause for the loss of seedlings.

Were Aloe pillansii or its fellow tree succulents to disappear from the Richtersveld, it wouldn’t merely be the loss of an aesthetically interesting plant, Midgley et al. added.

“Besides their human intrigue which encourages visitors to the area, they appear to be a moderate form of keystone species. They are often the only tall plants in an area and thus they are vantage points for raptors and are safe sites for birds which nest amongst the leaves or which bore into the stem.”

Little has changed since the article’s publication, despite above-average rainfall and favorable seed recruitment conditions in recent years. The likely fate of A. pillansii within the Succulent Karoo is summed up best by the description of its population on the 2009 IUCN Red List: “A serious decline in the population has reduced the numbers to less than 200 individuals. There is no recruitment and the older plants are dying.”

Comments are closed.