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Tuwaiq Mountain Range
Plant life in the mountains
The Tuwaiq Mountain Range is like a curved backbone down the middle of the Peninsula, stretching from the Nafud Desert in the north down to the Yemen border in the south. On the west side the mountains drop vertically to a flat-bottomed canyon with isolated pinnacles, sheer cliffs and narrow gorges on either side. In the rainy season the water gushes over the ledges forming little whirling pools and fast streams, spreading out when they reach the flat bottom of the valley and then gradually being absorbed into the parched earth. Even after the water has long disappeared, these dry river beds - are full of plant life.
The east side of the Tuwaiq mountains slopes down gently with many finger-like wadis dissecting the limestone plateau, which open into meadows offlowers in the rainy season. The upper reaches of the wadis have many large shady acacia trees, some over seventy years old. One of the largest and longest wadis is the Hanifah Wadi which passes through Riyadh. It starts high up on the back of the Tuwaiq Range about 100 ki lometres north-west of Riyadh and has many acacia trees growing along it. It is the old «Darb al Hijaz» (Road to the Hijaz and Mecca). The first farms start near the little village of Alayenah and from there to Riyadh there are many farms with palms, fruit trees, tomatoes and other vegetables.
In between the farms and along the rocky sides of the water there are many wiId flowers. The plateau is flanked on the east by ridges of sand - the Dahna Dunes - which curve down from the Nafud Desert to the Rub al Khali or Empy Quarter in the south-east. There are extensive pans of fine silt along the edge of the dunes, called raudha, which, with its diminutive riyadh, signifies valley of flowers. Quite often, in the rainy season parts of these pans are flooded to a depth of several feet, which may remain for two or three months. A carpet of annual plants surrounds these shallow lakes. The Raudha Kharaim, near Rhumah - about 100 kms. north of Riyadhis a favourite pasture for the beduoin and their livestock.
Somewhere deep inside there is a sliver of green which can transform the bush at the first shower of rain (Rhanterium). StiII others have fresh green leaves in the cool season but hard prickly ones in the summer like Blepharis ciliaris, whose deep blue flowers can be seen almost any month of the year.
The hard resistant seed cases of most of them are often protected by hardened sepals which close during dry weather but open up during damp weather to release the seeds (Anvillea). Many of the perennials are poisonous to livestock - Rhazyal Pergularial Calotropis. They mostly produce large seed pods with many seeds. The Acacia seed lings excrete a substance which is off other plantseedlings so reducing competition. The inflated calyx of the Astragalus spinosus can be blown far and wide, carrying the three or four seeds inside, for long distances from the parent plant.
Perennials have several ways of obtaining the all-important moisture. They may have very deep roots reaching down to the humid layers in the soil (Acacia) or they may secrete droplets of calcium chloride or magnesium solution through the skin of the leaves to attract and retain humidity in the air caused by difference in temperature from day to night. The plant can then use the water when it needs it.
Most of the perennials have very extensive root systems. The plants with bulbs have, of course, a store of food, however, they have long, slender leaves, which are tougher than those of more temperate climates. (Iris. Allium) All these plants have adapted in one way or another to the special conditions in which they live and so we find, even in the most inhospitable places, the bright beauty of a flower smiling up at us.