Haworthia tessellata 'Neat' shooting a bloom stalk. Can you see the windows in the leaf tops?

Haworthia tessellata is one of my favorite plants. At least that’s what I tell people. One friend has complained that I say that about so many plants that it can’t possibly be true.

The latin name tessellata comes from the tiled pattern in the leaf faces. Attractive, yes, but the bigger truth about these odd, waxy leaf faces is this: they evolved to be natural windows. Many Haworthia have adapted this way. Sunlight enters the plant body through these translucent windows and is converted into energy by many layers of chlorophyll-rich cells.

Haworthia limifolia, a close relative of H tessellata but lacking obvious windows in its leaves. It resembles opaque, molded plastic rather than translucent, carved wax.

This is especially useful in the arid climates where Haworthia tessellata makes its living; the primary photosynthesis tissues are not exposed to the drying elements.

Haworthia tessellata 'Fang', a select clone named for the teeth and tubercles on the leaf undersides.

Leaves with window tops are described as fenestrate, from the Latin for window: fenestra.

Haworthia tessellata 'Super Tessellata', a beautiful, select clone

What’s more, like many succulents, Haworthia tessellata can photosynthesize using Crassulacean Acid Metabolism (CAM). During CAM photosynthesis, the plant opens its stomata only during the cool of the night. It “inhales” in carbon dioxide and stores it in its thick, succulent tissues (while “exhaling” oxygen). During the heat of the day, the carbon dioxide stored deep in the plant can be used in photosynthesis because sunlight passes through the leaf windows, deep into the center of each leaf.

Haworthia tessellata (synonym Haworthia venosa ssp tessellata) is found many places in Southern Africa, especially central South Africa, also extending northward into Namibia. This stemless plant sends underground stolons up to 14cm (5.5 inches) away from the mother plant. This vegetative reproduction results in a mat of plants, and also makes it easier to propagate of select clones such as those pictured here.

See Also

Convergent Evolution in Succulent Desert Plants: Comparing Haworthia and Aloe (Africa) With Agave (America)

Breuer, Ingo. (2010). The Genus Haworthia – Book 1. Alsterworthia International. Softcover, Illustrated, 86 pages. ISBN 13: 9780955272677.
Breuer classifies Haworthia tessellata as a separate species, disagreeing with Bayer, who calls it a subspecies of Haworthia venosa.

Bayer, Bruce. (2003). Haworthia Update – Volume 1. Umdaus Press. Hardcover, Illustrated, 64 pages. ISBN 10: 1919766219

Court, Doreen. (Third Edition, 2010). Succulent Flora of Southern Africa. Cape Town, South Africa: Struik Publishers. ISBN-10: 1770075879. ISBN-13: 978-1770075870.

You can’t wade very far into the study of evolution, plant taxonomy — or the pursuit of growing exotic succulents at home — without smacking right into convergent evolution. That’s the notion that certain distantly related plants have evolved features which make them seem much more alike than their DNA (or evolutionary pedigree) would predict.

Hoodia pilifera, 3.5″ tall, like a tiny saguaro South Africa (Western Cape, Little and Great Karoo) photo by Sentient Meat

As I’ve learned more about it, I’ve come to the conclusion that there are two kinds of convergent evolution: the superficial, obvious kind and the subtle, fool-a-scientist kind. The more subtle kind of convergent evolution — the kind that can fool a scientist — shows up in the study of plant taxonomy (the classification of plants into species, genus, and family based on how closely they’re related). Just as DNA science has revolutionized how crimes are solved (and revealed that some imprisoned felons are actually innocent), the study of DNA in plants has revealed that plants once believed by scientists to be closely related (due to similarities in stem, leaves, flowers, or seeds) are actually quite distant relatives. They developed their similarities independently — and well after their ancestors had split off from each other. As a result, the family tree (for example, of Euphorbia¹) has been in a state of ongoing upheaval as the contemporary field of molecular phylogenetics revises our knowledge of evolutionary relationships and reveals many cases of subtle, scientist-fooling, convergent evolution.

Actual saguaro, approx 100x taller than our H pilifera photo by Leonard G. / Wikipedia – Creative Commons ShareAlike 1.0 license

In grade school we learn the more obvious kind of convergent evolution — a sort of gee-whiz, ain’t-Nature-grand, intercontinental shape-matching game, in which we are amazed that plants from Africa (like spiny euphorbs and today’s feature, Hoodia pilifera) bear such a striking, if superficial, resemblance to desert cactus (like the majestic saguaro, pictured), which hail exclusively from the Americas.
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