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In Lawrence of Arabia’s immortal phrase, the sword of summer has been drawn from its scabbard and lays most of us, even those tenacious flies and mosquitoes, low for months. Yet this is precisely when the splendid flowering trees of our streets and parks defiantly come into their own in a dramatic affirmation of continuing life. May and June are months when many trees and shrubs are ablaze with hot summer colours. No delicate pale European pastels here at the T-junction of Africa, Arabia and Asia – it’s all shocking pink, deep crimson, golden yellow, magenta and flame orange, more like the wild, passionate and often, to the Western eye, the violently clashing hues of Africa and India. They are the virile and sensual colours of blood, heat and hot spices, and they transform Oman’s urban landscape, shocking and dazzling us with vibrant pure colour.

But just how much do we know about these exotic and generous blooms? One or two are at home in Arabia, like Oman’s very own Nerium mascatense, better known as the oleander. This shrub has a smaller, deeper-pink flower than the cultivated oleander, Nerium oleander, which originally hails from the Mediterranean. The leaves are lance shaped and leathery, and the sap is milky. A hardy evergreen, it grows well in dry, sandy soils and can withstand heat and drought. All parts of the plant are toxic and a potential problem for children and animals, which might be tempted to eat it. It’s a pity, though, that although the cultivated variety is available in a huge range of colours, and in places like Galveston in Texas is a major attraction, the wild variety here is more often be seen brightening up barren wadis. The oleanders belong to the dogbane family, Apocynaceae, and their poison affects humans in a similar way to digitalis, a heart stimulant found in foxgloves. Oleanders are also known as the Rose of Jericho or the Rose of Ceylon, and come in almost all shades from deep crimson to white. Another local beauty, sporting the same deep pink, is at home in Dhofar but flowering in profusion now at the InterContinental Hotel in Muscat. This is the so-called Desert Rose, Adenium obesum. It’s not a tree, but a succulent shrub, with a weird grey swollen base and spindly branches. It’s actually African, but just squeezes in to southwest Arabia.

Because there are some 500 species of Cassia known worldwide, the large one most obvious in the area between the embassies and ministries in Muscat has escaped my attempts at definite identification. But all Cassia species, regardless of their size, from shrub to tree, typically have upright spikes of canary-yellow flowers with unopened buds at the top of the cluster that look rather like blackened popcorn. And almost all of them contain powerful laxative chemicals (perversely, ‘cassia’ is also the popular name for the fragrant cinnamon-like spice, but this is a mistake, as it doesn’t belong to this purging family at all). The trees have attractive, dark green feathery leaves, which set off the generous heads of flowers. Flowers of the Cassia family have an ingenious arrangement to aid pollination: each contains ten anthers, the male parts of the plant that produce the pollen. Nothing new about that. But two are large, five are middling, and three are small. So? Well, the eight smaller ones produce sterile pollen to attract bees and other insects that eat it. We know it’s a nutritious food for them, and plants produce pollen and nectar to bribe insects into pollinating them. Homing in on the smaller anthers of Cassia, however, the insects dislodge the pollen from the long anthers above them and get a liberal sprinkling of the real thing. With their hairy backs now dusted with potent pollen, the insects go off to visit the next flower and perpetuate the tree species.

But a smaller, more delicate member of the Cassia family is blooming right now, with long, dangling pale yellow blossoms contrasting with last season’s black seedpods. This is Cassia fistula, or the ‘purging fistula’, a rather unfortunate name for such a graceful lovely bloomer. Its beauty has given it a range of much more appealing names: Indian Laburnum, Amaltas and Golden Shower (not to be confused with the orange-flowered creeper of the same name). The drastic senna-pod extract that our great-grandmothers used to threaten us with when we were peaky comes from this family. You’ll recognise them immediately, especially from the area around the InterContinental. The long pod looks like a thin, dried black sausage. For the rest of the year, they hide modestly behind the large leaves, so catch them while they’re in their prime. The active chemical which shocks any lazy colon into action is anthraquinone. This tree comes from the Himalayan foothills, and is something of a cure-all in popular medicine. The root bark is an astringent and useful in treating blackwater fever, and Newcastle disease in chickens. The seeds are emetics, inducing vomiting. The leaves treat skin diseases; the fruit relieves rheumatism and the effects of snakebite; and the bark tans leather well. Most folk, though, just get on with appreciating the tree’s stunning gardening potential and give its ‘opening medicine’ a wide berth.

Without any quibbling, though, pride of place among flowering trees must be given to the Royal Poinciana, whose pre-eminent regal status is emphasised in its Latin name, Delonix regia. It can reach heights of 15m. Now a popular ornamental tree all over the drier tropics, its bravura performance begins with shedding all its tiny compound leaves for dramatic effect, and then putting out great clusters of fiery blossoms in a kind of reverse botanical strip-tease. Planted singly or in rows, the impact of these trees is stunning. On closer inspection, the blossoms, which can be up to 8cm across, reveal a palette of dazzling intensity which can vary from tree to tree: from deep, dark oxblood crimson to brick red, vermilion and flame orange, with speckles and splashes of yellow, or even the odd cream petal. In India it’s the Gulmohur. Its other popular names are Peacock Flower, Flame-of-the-Forest, Flame Tree and Flamboyant, the last like the name of the man who introduced it to the world, a Frenchman christened Phillipe de Longviliers de Poincy. The seeds are contained in 60cm-long, flattened woody pods, and give that Latin American instrument the maracas the right rattling effect. Oddly enough, it was only in 1932 that the natural home of the tree was traced to the dry forests of Madagascar, where it’s now a sadly endangered species in its wild state. We are fortunate in having a more muted, but still beautiful, wild member of the family in Oman. This is the white to pale-yellow or orange-flowered Delonix elata, happily a common tree in Dhofar, where it is one of the first to welcome the monsoon by budding in June; its flowers have long, red delicate stamens. In earlier times, its wood was used on the Salalah plain to make quicklime for building and plastering, and an infusion of the leaves eased childbirth for both women and livestock. The botanical garden in the grounds of Muscat’s Museum of Natural History has a nice specimen, together with other indigenous trees.

The tamarind tree, whose tart fruit flavours those English staples HP and Worcesterchire sauces, is naturalised in Oman. Although it’s scientifically Tamarindus indica, the ‘Indian date’, it is a native of tropical Africa, and probably made the move with prehistoric man to South Asia. It’s a fine, stately tree that can reach a venerable age. The timber is hard and dark red and is good for furniture making. It’s just a shame that so many of the older ones are being bulldozed in the name of urban development instead of being incorporated into new landscapes and gardens. The seeds are embedded in an acidic, Vitamin C- and potassium-rich pulp which makes superb sauces for fish or meat dishes and also a great polish for brassware and silver. In Indian ayurvedic medicine, it’s recommended for gastric problems and malaria, while all over the Middle East, it’s used for so many ailments as a tonic it really deserves its common name – tamar hindi is actually Arabic for Indian date. The tree’s yellow, recurved flowers are not as conspicuous as those of its other family members, but the brown segmented knobbly pods are distinctive.

Cassia, Caesalpinia, Delonix and tamarind trees are all related and classified as Caesalpinoideae, themselves all members of the huge Leguminosae family, to which peas and beans belong. All these plants are nitrogen-fixers, and thus help to recycle organic nitrates, one of the basic nutrients of life. With all these essential properties, trees and plants deserve closer study and nurturing, especially in this age of heightened ecological sensitivity with the dangers of global warming and environmental abuse. It is to the credit of the Ministry of Regional Municipalities, Environment and Water Resources that an ongoing programme of carefully selected planting and regeneration beautifies our surroundings. The species were all chosen for their visual effect and for their high tolerance of extreme heat and low water requirements. Spare a thought for the quiet army of gardeners assigned to take care of them and keep them trimmed and attractive, and hats off to those responsible for their selection.

And by way of conclusion, watch the rapidly ripening dates that are already festooning the palm trees. As summer draws to its long close, still deeper and more delicious tones will darken the dates: gamboge, carnelian, sepia, maroon, burnt umber, amber and liquid gold – a sensuous melting together of colour and taste, and well worth the long ordeal of summer. Like the blooms above, dates must be stimulated by intense heat to develop and mature. Summer in Arabia comes at a price, but has its own unique reward.