The Curly-Whirly Plants of South Africa

Gethyllis villosa

Gethyllis villosa

In a region of South Africa traditionally referred to as Namaqualand there exists a guild of plants that exhibit a strange pattern in their growth habits. These plants hail from at least eight different monocot families as well as the family Oxalidaceae. They are all geophytes, meaning they live out the driest months of the year as dormant, bulb-like structure underground. However, this is not the only feature that unites them.

A walk through this region during the growing season would reveal that members of this guild all produce leaves that at least one author has described as "curly-whirly." To the casual observer it would seem that they had left the natural expanse of the desert flora and entered into the garden of someone with very particular tastes.

Albuca  sp.

Albuca sp.

What these plants have managed to do is to converge on a morphological strategy that allows them to take full advantage of their unique geographical location. The region along the coastal belt of Namibia is famous for being a "fog desert." Despite receiving very little rain, humid air blowing in from the southwestern Atlantic runs into colder air blowing down from the north and condenses, carrying fog inland. This produces copious amounts of dew.

Normally dew would be unavailable to most plants. It simply doesn't penetrate the soil enough to be useful for roots. This is where those curly-whirly leaves come in. Researchers have discovered that this leaf anatomy is specifically adapted for capturing and concentrating fog and dew. This has the effect of significantly improving their water budget in this otherwise arid region. What's more, the advantages are additive.

The most obvious advantage has to do with surface area. Curled leaves increase the amount of edge a leaf has. This provides ample area for capturing fog and dew. Also, by curling up, the leaves are able to reduce the overall size of the leaf exposed to the air, which reduces the amount of transpiration stress these plants encounter in their hot desert environment. Another advantage is direct absorption. Although no specific organs exist for absorbing water, the leaves of most of these species are nonetheless capable of absorbing considerable amounts.

Dipcadi crispum

Dipcadi crispum

Albuca  sp.

Albuca sp.

Finally, each curled leaf acts like a mini gutter, channeling water to the base of the plant. Many of these plants have surprisingly shallow root zones. The lack of a deep taproot may seem odd until one considers the fact that dew dripping down from the leaves above doesn't penetrate too deeply into the soil. These roots are sometimes referred to as "dew roots."

I don't know about you but this may be one of the coolest plant guilds I have ever heard about. This is such a wonderfully clear example of just how strong of a selective pressure the combination of geography and climate can be. What's more, this is not the only region in the world where drought-tolerant plants have converged on this curly strategy. Similar guilds exist in other arid regions of Africa, as well as in Turkey, Australia, and Asia.

Albuca spiralis

Albuca spiralis

Photo Credits: Cape Town Botanist (http://bit.ly/1PzPkP7), www.ispotnature.org, roncorylus (http://bit.ly/1PzPoi6), and Wolf G. (http://bit.ly/1n4Mo6b)

Further Reading: [1]

A Curious Case of Gerbil Pollination

The hedgehog lily a.k.a. Massonia depressa hails from arid regions of South Africa. As with most plants from this region, it is highly adapted to its semi-desert environment. Its bizarre yet beautiful appearance belies something peculiar - a pollination syndrome that may surprise you. The hedgehog lily is pollinated by desert rodents such as gerbils.

Let's back up a second though. The genus Massonia has a certain level of confusion hanging around. For starters, despite its common name, it is not a lily at all. It was originally placed in the family Hyacinthaceae but now resides in the family Asparagaceae.

During the hot summer months this plant goes dormant, retreating underground in the form of a bulb. Come winter, two broad leaves are produced that lay flat on the ground. The positioning of the leaves may serve a few different purposes for the hedgehog lily. For starters, leaves laying flat on the ground may help the plant avoid herbivory. It may also help reduce water loss from both the underside of the leaves as well as from the soil surrounding its roots. Finally, it may also play a role in temperature regulation. Many different plant families in this region seem to have converged on a similar strategy.

Now let's get back to the flowers. Winter is also the flowering season. A stunning inflorescence is borne between the leaves. The cream colored flowers lay flush with the ground and are quite stiff. What is most peculiar about these blooms is that they emit a yeasty odor. All of these are adaptations for attracting its pollinators - rodents.

A study published in 2001 showed that when rodents were excluded from the flowers, seed set was highly reduced. Throughout the study, the authors noted four different species of rodents visiting the flowers at night. Two of these rodents were gerbils. Another adaptation for rodent pollination, albeit a subtle one, is extremely viscous nectar. The nectar of the hedgehog lily is 400 times more viscous than other nectar solutions with a similar sugar content.

This allows the rodents to effectively lap up the nectar, thus enticing them to visit the flowers more often. The authors also found that these rodents are often covered in hedgehog lily pollen throughout the blooming season. It coats their fur and makes up a large portion of their feces. Though this is not the only plant species to utilize rodents as pollinators, this is nonetheless a rare pollination syndrome.

Photo Credits: Graham Duncan, Kirstenbosch Botanical Garden and Steven D. Johnson, Anton Pauw, and Jeremy Midgley

Further Reading: [1] [2]

Snowdrops

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Few plants in temperate horticulture signal the end of winter better than snowdrops. Come February in the northern hemisphere, these herbaceous bulbs begin popping up, often through a layer of snow. They refuse to be beaten back by freak snow storms and deep frosts. 

Snowdrops are native to a wide swath of the European continent. Like many spring ephemerals, they love moist, rich forests and will often escape into the surrounding environment. Taxonomically speaking, there are something like 20 species currently recognized. From what I can tell, this number has and continues to fluctuate each time someone takes a fresh crack at the group. What is certain is that the original distributions of many species have been clouded by a long history of associating with humans. For instance, whereas Galanthus nivalis is frequently thought of as being native to the UK, records show that it was only first introduced in 1770. 

Because we find them so endearing, snowdrops have become commonplace in temperate areas around the world. Reproduction for most of the garden escapees occurs mainly by division of their bulbs. As such, most plants you see in gardens and parks are clones. Pollination in snowdrops is frequently quite poor. This has been attributed to the lack of pollinating insects out and about during the cold months in which snowdrops flower. Bumblebees are some of the few insects up early enough to take advantage of their white blooms and, when seed set does occur, the plants rely on ants as their main seed dispersers. 

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Contrary to their ubiquitous presence around the globe, the IUCN lists some snowdrop species as near threatened in their home range. The genus Galanthus contains some of the most heavily collected and traded wild bulbs in the world. Pressure from the horticultural trade coupled with habitat destruction and climate change may push some species to the brink of extirpation throughout Europe in the not-so-distance future. 

Photo Credit: [1] [2]

Further Reading: [1] [2] [3] [4]

http://www.arkive.org/snowdrop/galanthus-nivalis/