There is a small and unusual grouping of plants in the arid regions of the world which have coiled, spiraled, or wavy leaf forms, as opposed to the typical narrow and straight, or wide and flat leaf shapes seen on most other plant species. Several theories have been floated as to why coiled leaves have evolved in dry regions, and especially in windy ones. One is that these twisted leaf shapes are more resistant to motion induced by strong winds, since they roll around without as much fraying and rebound a bit like springs when moved sideways back and forth repeatedly. Another is that coiled leaves are photosynthetically efficient, since a good portion of the leaf surface is always exposed to maximal sunlight at the right angle no matter what time of day.

Since most twist-leaved plants are small bulbs in winter-rainfall climates, the short and cool days demand that increased photosynthetic efficiency is a priority, especially on limited water. Shown here are three African species and one North American alongside a discussion of how this leaf arrangement might confer a survival advantage upon the plants.

This is probably Albuca concordiana, a relatively sizable spiral-leaf bulb found in the Little Karoo region. Even with flowers, Albucas are hard to separate accurately.

The tightly coiled leaf spirals of Albuca concordiana act like springs that rebound from wind motion and do not whip around, unlike the movement of grasses in a meadow for example. While wind motion might not present much of an issue in grasslands that get adequate rainfall, it can damage the small leaves of bulbs that live in very arid habitats with narrow margins of survival. Spiraling prevents much leaf thrashing and the low profile offers further protection as well as water conservation capacity.

Albuca concordiana flower in the Little Karoo near Calitzdorp, Western Cape in September 2016.

The curly leaf shapes of Albuca concordiana resemble metal filings that come from a drill press, at least in shape if not exactly in color.

It is important to note that these curly leaves are not the same thing as tendrils, which are grasping structures found on many familiar climbing plants (like grapes, sweet peas, and squash) which help those species scale rocks, walls, nearby tree trunks, and so forth. Tendrils have a superficially similar appearance, but entirely different purposes, and are usually separate organs present in addition to true leaves. Tendrils may be modified from structures such as leaves, leaflets, leaf tips, or leaf stipules, or even be derived from modified stem branches. But they are generally not the leaf itself.

Moreover, tendrils are tactile and responsive to touch, which is why they reach towards and wrap around nearby objects they encounter, since their purpose is ultimately to support the plant stem they are growing off of as it climbs towards the sunlight. None of these traits apply to the spiral leaves of these bulbs. I add this as a fine point of discussion to better explain why spiral leaves and tendrils are different features with different origins and ecological purposes , since they otherwise might be confused due to similar appearances.

This might be Albuca spiralis, a species with thin, thread-like leaves. Again, without blooms these can be hard to positively identify. There are perhaps 15 to 20 different bulbs in southern Africa in several families and genera that exhibit this leaf growth pattern.

Above is a remarkable example of a spiral-leaved bulb, Trachyandra tortilis, grown in a pot by my Facebook friend Alain Christophe of Plantemania in France. It’s one of the most extreme examples of this, on top of the unusual stacked ribbons look.

Ajo lilies flower on sand dunes near the Colorado River in early March 2017.

While generally speaking the most diverse array of leaf-spiraling plants is located in southern Africa, there are related examples elsewhere, including bulbs in Chile’s Atacama Desert, and in North America’s Sonoran Desert. The photo above depicts probably the most prominent example in the United States, the Ajo lily (Hesperocallis undulata) of Arizona and California. While the leaves of Ajo lily, also known as desert lily, are not tightly spiraled they do have a strong wavy edge as well as a tendency to curl. Both of these shapes help the lilies’ leaves resist excessive motion in their often windy sand dune habitat, which again reduces fraying and wind damage.

Additionally, since the lilies often emerge in the coldest winter months, the various crisped leaf margins are always somewhere exposed to the best sun angle, which maximizes photosynthetic efficiency on short, chilly days. For bulbs living on dry sand dunes it is important to be as efficient as possible with water use. This is why they grow during the cold short days of winter, which does reduce water loss, but costs the plants in terms of it not being the best time of the solar cycle for food production. And since they must expend energy on leaf production at this time of year when winds can be strong, it’s similarly important to not let the leaves be damaged too much via excessive motion.

Welwitschia mirabilis growing in Namibia’s Namib-Naukluft National Park in May 2018.

One final example of an extremely arid-adapted plant that has a strong tendency to grow wavy leaves is Welwitschia mirabilis, a bizarre ancient coniferous plant from Namibia and Angola in southern Africa’s Namib Desert. While neither a small bulb nor a monocot like the other species shown above, welwitschias have a similar growth habit and share a hyperarid ecosystem. The thick, leathery leaves of welwitschias do not really spiral, but as seen in the photo above many of them develop large waves that again, resist motion.

Unlike the other examples in this post, welwitschias are perennially above ground and do not die back to subterranean bulbs like the Albuca and Hesperocallis plants do. They do not have the “luxury” of avoiding the dryness of the Namib Desert – they face it alone, all day, all year, for millennia. The oldest individual welwitschia plants are thought to be over 2000 years old. To live that long in such a dry desert requires special adaptations, one of which is again, leaf waviness that resists wind. I’ll discuss more on the amazing welwitschia in another post soon.

Isn’t life amazing in how it adapts over time?