Desert Plant Adaptations (III) ~ Drought-escaping Plants

I’ve written about two general strategies that plants employ to survive in desert habitats – succulence and drought-deciduousness. Today I’ll introduce the most successful adapters to life in the desert – drought-escaping plants. Plants escape drought in one of two ways. They either survive only as seeds or they use taproots.

Annuals are plants that wither and die during the dry seasons but not before completing their life cycle, sometimes in just a few weeks. Their seeds are covered by a thick protective coat and are dispersed, only to wait underground as part of the desert’s “seed bank”. Contained within their seed coats are certain chemicals that prohibit germination. The seeds must wait for rain to wash these chemicals away before they can sprout. These are the plants that amaze us here in Sinai when our desert sands are suddenly covered in green after a spring rainstorm. These are also the plants that are so important to the Bedouins’ herds of goats and sheep. Some of these annuals that survive dry seasons as seeds include Astragalus spp., Artemisia spp., Diplotaxis spp., and Tribulus spp. and are pictured below.

Using taproots is also a successful strategy to avoid the problems associated with drought. A taproot is a very thick and long root that grows directly downward. Think of a carrot. The taproot is the main central root which other smaller roots grow off of. The long taproot allows the plant to reach water stored deep underground, providing an almost constant source of water. The taproots of Convolvulus lanatus, pictured below, and Artemisia monosperma are also covered with a thick bark that helps the roots to withstand the withering caused by wind.

You can learn more about these desert plants in my book, Wandering through Wadis: A nature-lover’s guide to the flora of South Sinai.

Desert Plant Adaptations (II) ~ Drought-deciduous Plants

It’s been longer than I had planned, and I’m not sure where the time went (well, a lot of it went to waiting for a new computer when my old one bit the dust), but I’m finally back with more information about how the plants in South Sinai have adapted to survive the harsh desert conditions! In the first installment of this series, I talked about succulence, the ability of plants to store water in their leaves, stems, and/or roots.

Lycium shawii, Desert Thorn

Today, I’ll discuss drought-deciduous plants. Instead of storing water like succulents, these plants use a different method to deal with drought conditions. During the dry seasons, they drop their leaves, allowing them to save water that would otherwise be lost during transpiration (similar to sweating in humans).

Because these plants don’t have their leaves to make food in the summer, their stems take over the photosynthesis process. (More on this in a future post.) Drought-deciduous plants also slow down their metabolism, making only enough energy to keep the plant alive. This means when conditions for growth are favorable again, the plants don’t have to start from zero. They’re already idling and ready to go, if we think in car terms; they don’t have to turn the ignition on first.

Lycium shawii, or Desert Thorn, is one example of a plant that is completely leafless in the summer. (It also has succulent leaves, so more than one adaptation to help it survive.) And because I don’t hike in the summertime, I don’t have photographs of this plant without leaves. But here’s a pic of their beautiful lush leaves:

In my next post, I’ll discuss the most successful adapters to life in the desert – the drought-escaping plants – so be sure to follow the blog or the Facebook page so you don’t miss out!

Desert Plant Adaptations (I) ~ Succulence

Plants that have adapted to living in dry habitats are called xerophytes, and they are the characteristic plants of deserts and semi-deserts. Over the next few weeks, I’ll be explaining some of the adaptations that allow them to survive in such a harsh desert environment. And it is harsh! Besides the limited supply of water, these plants must also survive high daytime temperatures, high levels of solar radiation, high levels of salinity, and strong winds. Water, however, is the most important ingredient in their lives and they must prevent water loss and overheating to survive. In general, to overcome these obstacles, desert plants can be classified into three main groups according to how they deal with the drought conditions – succulence, drought-deciduous, and drought-escaping. Today, I’ll talk about succulence.

Succulence is the ability of plants to store water in their leaves, stems, and/or roots. Cacti are a classic example. Succulent plants have shallow roots, allowing them to quickly absorb any available moisture, including dew. These plants can begin to grow 24 – 48 hours after rain. You may have noticed that there aren’t many cacti growing in the wadis of South Sinai, but there several species of succulents.

Species with Succulent Leaves

If you think back to your high school biology class, you’ll recall that photosynthesis is the process that allows plants to use the sun’s energy to convert carbon dioxide (CO2) and water into sugar. Basically, it’s how plants make their food. There are pores, called stomata, on the leaves that open and close to absorb carbon dioxide from the air and release oxygen. When these stomata open and close, water vapor is also released and evaporated. This release of water is called transpiration. It’s similar to sweating in humans and can help cool the plant. And we know that if we sweat a lot, we should drink more water to stay hydrated. However, desert plants do not receive a lot of rain to replace this lost water. So they have adapted to conserve as much water as possible.

Species with Succulent Stems

One way succulents do this is to use a different type of photosynthesis, one that allows the plants to make food without losing a lot of water to transpiration. It’s called crassulacean acid metabolism, or CAM photosynthesis. Plants that use CAM open their stomata at night when temperatures are cooler and keep them closed during the day. Instead of using sunlight to convert the CO2 to food right away, plants store the CO2 they absorbed at night as crassulacean acid. As the day begins and the temperature starts to rise, the acid is changed back into carbon dioxide and then used in photosynthesis. This allows the plants to conserve water and use it to make food instead of losing it to evaporation.

Species with Succulent Stems and Leaves

That’s a pretty fascinating adaptation, isn’t it? But it’s only the start! Stay tuned for my next post where I’ll discuss drought-deciduous and drought-escaping plants.

Stagshorn Lavender

Many people are surprised to learn that lavender grows in the desert wadis of South Sinai.

Stagshorn Lavender (Lavandula coronopifolia) is one of 47 lavender species in the Lavandula genus and one of two that are native to Sinai. While not as fragrant as its cousins, the leaves of Stagshorn Lavender do have a pleasant scent and are edible, grazed by the local herds of goats, sheep, and camels.

And I can attest to their tastiness! When I had a plant growing in my desert garden, we often added the leaves to our salads.

It is in fact their distinctively branched stems that gave this species its common name – stagshorn. In Arabic, this plant is known as zeiti, diktae, or netash.

Stagshorn Lavender is a small shrub in the mint family and can grow up to one meter in height. Lavandula coronopifolia grows in open rocky habitats, desert plains, and foothills and is the most widespread species of lavender across northern Africa.

The flowers are sky blue to lilac in color and bloom between January and April.

Which means you can seem them in bloom right now! When I was wandering through wadis last weekend, the lavender plants were one of the few plants with flowers. There would be more if the area had received more rain this season, so my fingers are crossed that the small chance of rain forecast for tomorrow comes through!

You can find Stagshorn Lavender – and over 140 other plants – in my book, Wandering through Wadis: A nature-lover’s guide to the flora of South Sinai. Purchase a PDF copy online here.

Dead Sea Apple Tree

The Dead Sea Apple Tree (Calotropis procera) is one you are more likely to see growing in the coastal plains of South Sinai rather than the mountain wadis. They are easy to spot along the main roads and even in the main cities of Dahab and Nuweiba.

Called ‘ushaar ( العشار ) in Arabic, this is a small tree in the dogbane family. It can grow up to four meters in height and the bark is light brown and cracked.

The leaves are large and grayish-green in color and are a popular meal for the larvae, or caterpillars, of the African Monarch Butterfly (Danaus chrysippus).

The small flowers, which grow in clusters, are some of my favorite – small and white with purple tips. They bloom from May to November and are pollinated by Carpenter Bees (Xylocopa sp).

The fruits are large, bright green and inflated like a balloon.

The fruits were traditionally used by the Bedouin of South Sinai as floats for fishing nets and the fibers used to make skull caps as well as stuffing for cushions.

When they are fully ripe, the fruit bursts open, releasing hundreds of seeds with fine, long, white hairs. It is common to see the seeds floating through the air in springtime.

So common in fact, they starred in one my children’s books, The Flying Seed, which you can read and download for free at my Books by Habiba blog where you can find a few other nature-related titles.

Although beautiful, this plant leaks a milky acrid sap when broken that can cause possible irritation to the skin and, I’ve heard, vision impairment.

Calotropis procera is also known as Sodom Apple, Sodom’s Milkweed, Rooster Tree, and Rubber Bush and is one of many plants mentioned in the Bible and Quran.

You can find this plant, and over a hundred others, in my guide book, Wandering through Wadis: A nature-lover’s guide to the flora of South Sinai.

Samwa

Samwa (Cleome droserifolia) is one of the most popular medicinal herbs in Egypt and a common one to come across in the wadis of South Sinai, including around Dahab. It also has one of the most beautiful blooms.

Samwa is an aromatic shrub covered in glandular hairs that give off a distinct scent, one that can sometimes greet you several meters from the plant. I find its sharp fragrance quite pleasant, but not everyone agrees with me.

Samwa grows in rocky, gravelly, and sandy desert wadis and plains. Older bushes are round and can grow quite large, up to 60 cm high.

Bedouin of South Sinai use samwa medicinally to treat a variety of ailments in both people and animals, including bee stings, internal and external infections, and diabetes.

When you stop to have a closer look at samwa bushes, you’re likely to encounter Green Lynx Spiders.

Green Lynx Spider with egg sac on a samwa bush

You can learn about samwa and more than one hundred other plants growing in South Sinai in my book Wandering through Wadis. Check it out.

Wild Mustard ~ Jahag

During the recent Christmas holidays, I spent a day with my family on a desert safari near Wadi Arada. This area has already been blessed by winter rains, so I was thrilled to see some of my favorite plants already sprouting – and in bloom!

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This is a type of wall-rocket (Diplotaxi acris), a wild mustard in the cabbage family, called jahag or yahag by the Bedouin. It is one of the species that appears shortly after seasonal rains in desert plains.

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It is an annual plant with alternate, serrated-edged leaves that grow out from the base in a rosette formation. The leaves are juicy and peppery-flavored and make a tasty addition to a fresh salad. Of course, the goats, sheep, and camels like to graze these greens as well.

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The four-petaled flowers, also edible, are white to pinkish-purplish in color. There is a related species in Sinai, Diplotaxi harra, that has yellow flowers.

Bir Safra Area (53)

Have you ever seen jahag on your desert adventures? Have you ever tasted it?

To learn more about the flora of South Sinai, check out my book, Wandering through Wadis.