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.

Giant African Mantis

While you’re more likely to come across an Egyptian Flower Mantis in the wadis of South Sinai, Giant African Mantises are more often spotted in cultivated gardens.

Also called African Mantis or Bush Mantis, this species (Sphodromantis viridis) is a popular pet around the world. They are native to West Africa, south of the Sahara, so are an introduced species here in Sinai.

I am always so excited to find them in my desert garden. And while I don’t keep them as pets, I have been known to hand-feed them flies that I have swatted inside my house.

Like all mantises, they have a triangular head and forward facing eyes that give them binocular vision, a great advantage in catching prey. Their color can range from bright green to dull brown and are often cryptically-colored to match the background of their habitat. Females can grow up to 10 cm in length and males are always smaller. As adults, both have distinctive white spots on their wings, which you can see in the photo below if you look closely.

Males will frequently become victims of sexual cannibalism, being eaten by the females prior to, during, or after copulation. A few days after mating, the female will produce one – or several – ootheca, or egg mass.

The eggs are laid on a twig in a frothy, foam-like substance that then hardens. After three to six months, up to 300 nymphs can hatch from a single ootheca.

Mantises develop by gradual metamorphosis, molting six to nine times or more. Each time they molt, their hard exoskeleton splits and a soft-skinned mantis pushes itself out. This allow for a larger exoskeleton to grow. As they wait for their new skin to harden, they hang upside down and are quite vulnerable to predators, particularly birds. The time range between molts is usually nine to fifteen days and the mantises will eventually become adults and develop wings.

Besides lacking wings, the abdomens of nymphs are folded, but they are still skillful ambush predators, waiting quietly for prey to approach.

They are general predators, eating all types of arthropods – mosquitoes and gnats when the mantises are small and moving on to larger critters like bees, moths, grasshoppers, and crickets as they grow. They will even eat other mantises.

They have grasping front legs to catch and hold their prey and extremely strong mouth parts.

An interesting side note: praying mantises may have had religious significance in Ancient Egypt. It might have been believed that the mantises served as guides to the deceased on their journey to the afterlife. And in one excavation in Luxor, a small clay coffin was found that held the remains of a praying mantis wrapped in linen.

Have you spotted a Giant African Mantis in Sinai?

Blister Beetles

Blister beetles, in the Meloidae family of beetles, earned their name from their defense system. They secrete a caustic chemical, cantharidin, which is an effective repellent for predators and can cause blisters on the skin when the beetles are handled.

The bodies of blister beetles are usually long and slender and often bi-colored. Their antennae are threadlike or beadlike.

Blister beetles use their strong jaws to chew the flowers and foliage that they feed on.

Mylabris sp.

The bright red and black pattern on the blister beetle pictured above is a warning sign of their toxicity to predators.

Mylabris sp.

Sinai Agama

A common critter to come across in the wadis, the Sinai Agama (Pseudotrapelus sinaitus) is known in Arabic as qadi sina’, or the “judge of Sinai”, due to a stance they take – raising themselves high up on their limbs and tilting their head.

Males take this stance when they sit in prominent look-out locations, defending their territory. Sinai Agamas also raise themselves up to avoid the extreme heat of the rocks. Notice that the toes are also not in full contact with the hot ground.

Sinai Agamas have triangular-shaped heads with large ear openings in line with the mouth. They are slender lizards, their body up to 10 cm in length, with long, thin limbs. Characteristic of this species, their third hind toe is longer than the fourth.

Their color varies greatly between the sexes and depending on the breeding season, during which time the head, throat, and neck of the males become a bright blue and females display several red-brick bands on their backs.

Sinai Agamas live in dry, rocky mountainous and hilly areas. They are ectothermic, or cold-blooded, and active in the hottest part of the day. You can often find them basking in the sun atop boulders, cliffs, and piles of stones. If you’re quiet and don’t make any sudden movements, I’ve found the agamas will stay put and let you admire them for a few minutes (which is one reason I have so many photos of these adorable lizards).

Maybe it’s because I spot them in cooler weather, when their metabolism is lower. Typically, apparently, when alarmed, the Sinai Agama will quickly run off. Unless the outside temperature is lower and they are incapable of sudden bursts of speed. Then their instinct it to stand their ground and attack their aggressors.

I came across a Sinai Agama in Wadi Beida once. He was a couple of meters ahead of me when I spotted him and stopped to take a photograph. He had noticed my presence and as I photographed him, his head turned more and more blue. He then turned and ran full speed at my feet, as if he was going to attack me. I didn’t move. Neither did he. After a moment or so, he turned around, headed back to the boulder he had come from, and went back to munching on ants as I continued to photograph him. It seemed he had accepted I was no threat to him and could carry on as usual.

The Sinai Agama that “attacked” me

Sinai Agamas feed on insects, mainly ants, and other arthropods, as well as plants. They are “sit-and-wait foragers” and agile climbers, darting off quickly to chase after insects when they spot them nearby.

Sinai Agamas are one of my favorite critters to encounter while wandering through wadis! What are yours?

References:

Aly, D. & Khalil, R. (2011). Wildlife in South Sinai. Cairo.Funded by the E.U. in cooperation with G.O.S.S.

Baha El-Din, Sherif. (2006). A Guide to the Reptiles and Amphibians of Egypt. Cairo: The American University in Cairo Press.

Wikipedia: Sinai agama

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.

Flower Crab Spider

Crab spiders are abundant in my desert garden at home and can also be spotted out in the wadis. Belonging to the Thomisidae family of spiders, they earned their common name from the way they extend their front pairs of legs in a crab-like fashion.

Female Flower Crab Spider (Thomisus citrinellus) on a flower bud of a caper bush.

Flower crab spiders belong to the genus Thomisus and there are about 150 species worldwide. They earned their name from the fact that they are ambush predators, sitting and waiting motionlessly in or nearby flowers for prey to approach. Today, I will introduce you to the Flower Crab Spider Thomisus citrinellus.

Female Flower Crab Spider (Thomisus citrinellus) on horsemint (habaq) flowers.

Like all crab spiders, the males are much smaller and differently-colored than the females. Female spiders can vary in color – I’ve seen both yellow and white – and the color may depend or change according to the surrounding vegetation. They range from 5 – 7.3 mm in size, whereas males grow from 2.1 – 2.6 mm long. Females usually have dark spots on the points of their abdomens. The first two pairs of legs are longer and thicker and have spines. On the first pair of legs, there are four distinctive dark bristles, often seen as dots in the field. These dark bristles distinguish this from other similar Thomisus species.

Female Flower Crab Spider with a male riding piggyback.
Male Flower Crab Spider (Thomisus citrinellus) on a caper flower.

Flower Crab Spiders prey on a variety of insects – flies, hoverflies, bees, and sometimes other spiders.

Thomisus citrinellus with prey (hoverfly).
Thomisus citrinellus with prey (fly).
A white female, with a male riding piggyback, preying on a yellow female.

Flower Crab Spiders do not build webs, but they will spin silk thread to use as a drop line or to fold leaves into a tent-like structure where they can hide in ambush. Eggs are also laid in a silk dish covered with a lid.

Thomisus citrinellus with silk folding a leaf of a caper bush.
Thomisus citrinellus with its silk drop line visible.
A baby Flower Crab Spider (Thomisus citrinellus)

Common Black Scorpion

In all my time in the deserts and wadis of South Sinai, I have encountered scorpions only twice. And that’s okay with me. They kind of creep me out, just like their arachnid cousins, spiders, used to. But I’ve learned to love spiders and so maybe one day I’ll feel differently about scorpions too. Indeed, I was simultaneously freaked out and fascinated when we encountered this Common Black Scorpion (Nebo hierichonticus) in a wadi last spring.

Common Black Scorpions can grow up to 11 cm in length, not including the tail. Their color ranges from light or reddish brown to dark brown with their legs and large pincers being slightly lighter in color.

I was relieved, once I was able to identify this scorpion, to learn that while their venom is quite toxic, causing hemorrhage and necrosis to small prey, their stings are generally harmless to humans, being compared to the sting of a honeybee. The scorpions prey mainly on big insects and spiders and sometimes on small vertebrates like geckos.

Common Black Scorpions live in and under big stones and rocks or in cracks and burrows in deserts and arid mountainous regions.

Sinai is home to a variety of scorpion species, including two of the most dangerous in the world – the Arabian Fat-tailed Scorpion (Androctonus crassicauda) and the Death Stalker (Leiurus quinquestriatus). You can also find Egyptian Pillar-tailed Scorpions, Egyptian Sand Scorpions, and Large-clawed Scorpions in Sinai, although this list is not exhaustive.

The Bedouin of South Sinai “have devised their own version of a primitive vaccine that is believed to provide their children with immunity against venomous stings of scorpions and wasps.” The process of immunization differs among tribes, but for the Jebaliya tribe, it involves collecting, roasting, and grinding a spider wasp and a young Death Stalker scorpion along with a bit of sugar. To this powder, spit from someone believed capable of passing on their immunity is added. This mixture is then given to a child sometime before they eat their first solid food.*

References:

*Aly, D. & Khalil, R. (2011). Wildlife in South Sinai. Cairo.Funded by the E.U. in cooperation with G.O.S.S.

Jericho Scorpion – Nebo hierichonticus – Mahmiyat.ps