Desert Plant Adaptations (IV) ~ Leaf Adaptations

Getting back to my series on desert plant adaptations, let’s discuss some of the ways that leaves have adapted to help plants survive the hot and dry conditions of the desert wadis.

Besides dropping all of their leaves like drought-deciduous plants, some plants simply have smaller or fewer leaves. Smaller leaves means there is less surface area open to the wind and sun, and so less water is lost through transpiration. Semi-shrubs and shrubs may have large leaves in the winter that are shed during the dry season and are replaced with smaller leaves in the summer. Artemisia herba-alba and Phlomis aurea both have smaller summer leaves.

Another strategy that helps conserve water is folding or rolling up the leaves so that the stomata are facing inwards, reducing the surface area subject to transpiration. This adaptation is employed by Helianthemum species, Fumana thymifolia, and many perennial grasses.

But it’s not just transpiration that leads to water loss. Leaves also lose water through their cell walls. To combat this, the leaves of some desert plants have a waxy coating or a thick cuticle, the film covering the surface, which helps seal in and protect moisture already in the leaves. Most xerophytes have a thick cuticle.

Hair on the leaves and stems also helps reduce water loss by providing shade and trapping water vapor near the plant’s surface. Artemisia herba-alba, Phlomis spp., Majorana syriaca, and other plants utilize this adaptation.

Plants needs energy from the sun to photosynthesize. What energy they don’t use to make food is used to heat the leaf up. That is very useful for plants growing in cold climates whose leaves need to be a bit warmer to photosynthesize but not so necessary for desert plants, which must reflect some of this solar radiation or risk over-heating. How do they do this? Some plants, like Capparis sinaica, have a waxy coating on their summer leaves which gives them a lighter – and more reflective – color than their winter leaves.

Leaves of Atriplex species also have a different color depending on the season, but they don’t use a waxy coat. Instead, the leaves are covered in vesicular hairs that contain a salty solution. In the winter, the hairs are full and transparent, allowing more absorption of the sun’s energy. In the summer, the water evaporates and the hairs dry out causing the leaves to be a lighter color that reflects the sun’s rays.

You can read more about each of the species photographed above in my book. In the next post in this series, we’ll learn about stem adaptations. Stay tuned!

Pantropical Jumping Spider

Over the past several years, I have really come to enjoy watching the jumping spiders in my garden and, of course, while wandering through wadis. The Pantropical Jumping Spider (Plexippus paykulli) is one of the more common – and dramatically-colored – ones that I can see close to home.

I was not surprised, then, to learn that this species is often associated with buildings and man-made structures and may be found near light sources.

Both sexes of this species have a high carapace (upper section of the cephalothorax, the front part of the body where the legs are attached) and are covered in short grayish hairs.

Males, pictured above, have a black carapace and abdomen with a broad white stripe running through the center. There are also broad white stripes along the sides and a pair of white spots towards the rear end of the abdomen. The face appears to have three white stripes, which you can see clearly in the close-up photo below.

Immature spiders, as well as females like the one pictured below, are brownish-gray in color with a broad tan stripe through the center of the carapace and abdomen. Towards the end of the abdomen, the stripe breaks into chevrons, v-shaped marks.

Like all jumping spiders in the family Salticidae, Pantropical Jumping Spiders have incredibly acute eyesight. They have four pairs of eyes, with the middle pair in the front quite a bit larger than the others.

“Hoppeedderkopp” by hornet81 is licensed under CC BY-ND 2.0

These jumping spiders do not spin webs. Instead they use their silk to build ‘retreats’ in high-up places where they can rest safely when not hunting. Once they have spotted potential prey with those amazing eyes of theirs, the spiders go into stealth mode and approach, leaping only when they are close enough, but not before attaching a dragline. And these spiders can jump! They can cover many times their body length in a single leap.

These aptly-named spiders will pounce on and eat flies, bugs, bees and wasps, butterflies, dragonflies, grasshoppers and other spiders. They can reportedly kill prey that is twice their size. They do this by first injecting the prey with venom and then overpowering them by brute force while the prey is still mobile.

Desert Mantis

Camouflaged against the stones and gravel, desert mantises (Eremiaphila spp.) are so cryptic that they are difficult to spot unless they are moving.

They are well-adapted to arid habitats, and there are 31 different Eremiaphila species recorded in Egypt.

Desert mantises are voracious ambush predators, waiting patiently until their prey is spotted and then pursuing their victims quickly and grasping them with their spiked forelegs. Because their hunting relies heavily on vision, desert mantises are diurnal, or active during the day. They are very flexible, able to move their heads without moving their whole bodies, allowing a large field of vision.

Although flightless, adult desert mantises have small wings, as seen in the magnified inset below.

Have you spotted desert mantises on your wadi wanderings?

Huntsman Spider

I have not been able to photograph a huntsman spider yet, but a friend in St. Katherine has and generously shared her pictures so I could write a post about this beauty!

This is a spider in the huntsman family of spiders (Sparassidae), specifically Eusparassus walckenaeri. There are 33 spiders in the Eusparassus genus, and they can be found in Africa, Asia, Europe, and Peru. Huntsman spiders are known for their incredible speed. In fact, it’s because of their lightning speed that the Jebeleya Bedouin call them beraira.

These huntsman spiders are large with flat bodies that are dark brown to orange-brown in color, with a pattern of spots and chevrons. The bodies can be from 1 to 2.5 cm in length, with the females being larger. The legs have dark bands of color and, although the legs of most spiders are perpendicular to their bodies, the legs of huntsman spiders are not. Their legs are angled and twisted in such a way that they move with a sideways crab-like motion. (Huntsman spiders are sometimes called giant crab spiders.)

Huntsman spiders are nocturnal hunters and feed on small and large insects, especially cockroaches, so a spider would be a welcome find in your home! And there’s no reason to be afraid of them; their venom won’t hurt you.

While these spiders may be imposing hunters, they are, of course, prey to other animals, especially to a family of wasps known as “spider wasps” (Pompilidae). A female spider wasp uses its venomous sting to paralyze a spider and then drags the spider to her nest or burrow. There, she lays an egg on the spider, which is anesthetized but alive. The wasp larva hatches and proceeds to feed on the spider, saving the vital organs for last, until it finally spins a cocoon and eventually emerges as an adult wasp.

These huntsman spiders can be found in open ground, but I have never spotted one in the wadis. They can also be found indoors and I’m pretty sure I have seen (some species of) huntsman spiders scuttle through the communal seating area of a camp in Ras Sidr. Have you spotted these huntsman spiders in South Sinai?

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

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.

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?