Botanising in the UAE
Updated: Dec 11, 2020
Al Hajar Mountain range in the United Arab Emirates (UAE) makes up part of the eastern border of the country, shared with Oman. The range forms an impressive divergence from the rolling deserts that make up 80% of the UAE’s land mass. Thrust from the oceanic crust around a hundred million years ago, the Hajar Mountains are rough and jagged. The rocks are predominantly metamorphic with a low silica content. Erosion leads to very alkaline, nutrient deficient soils. Rust-brown in colour, they are especially attractive when the sun is low in the sky at daybreak and sunset.
The mountains are home to the highest concentration of native plant diversity in the UAE, where differences in altitude, aspect, hydrology, temperature, and bedrock provide suitable habitats for plants to establish.
Exploring the mountains is quite easy, much is open and accessible. From experience, the ascent is best done by first finding a wadi (valley) running down the mountainside and bouldering up its path. Climbing is relatively easy, as you ascend, but there are a few major factors to bear in mind. Firstly, rocks can be incredibly fragile and crumbly, so great care needs to be taken when exploring.
In my experience, rocks within the wadi beds are either more stable to clamber over or comprise scree that can be scrambled over. Secondly, wadis can rapidly become raging torrents of water, so ensure no rain is forecast. Finally, you are unlikely to encounter anybody during an expedition, so make sure you are self-sufficient in water and food and inform somebody of your route and return time. Mobile phone signal is generally good, but like most remote places, there are areas where the signal fails to reach.
North-facing wadis can be especially rewarding to climb, as these are protected from the harshest summer weather and hence have greater plant diversity. The composition of vegetation changes as you increase in altitude. At around 600m you start encountering plants not found at lower altitudes and unsurprisingly this pattern increases the higher you climb. Although the mountains are not high by world standards, the zonation of different plants is distinct.
From 600 meters, you may be lucky to find two attractive members of the dogbane family (Apocynaceae), Desmodorchus arabica with purple flowers and D. flava with yellow blooms. These two species are rarely seen in the UAE. Some accounts suggest both are rare and endangered, but those with sharp-eyes and in the right location are likely to encounter several during a day’s hike. They are cryptic species due to the colouration of their succulent stems, and in my experience tend to grow beside large rocks. It would be easy to wander right past them and never notice, which probably accounts for the suggestion that they are rare.
When not in bloom the two Desmodorchus species are all but impossible to distinguish. If they happen to be in flower their unpleasant, carrion-like smell may be the first indication of their presence. The odour is not overly strong, but if you end up being downwind you are sure to notice.
Desmodorchus belongs to the subfamily Asclepiadoideae. This family’s flowers are some of the most elaborate and complex in the flowering kingdom, and to that extent, comparable only to orchids. Looking more closely at the ends of D. arabica and D. flava’s petals you may notice feather-like projections. They are not visible on all flowers, so may be associated to a developmental stage of the plant. These projections wave in the wind, and I had first assumed they were glandular and associated with scent dispersal. However, discussions with Professor Diego Demarco, of the Laboratory of Plant Anatomy, University of Sao Paulo, Brazil suggests their function is unknown at present (So, any suggestions to their purpose, please add them to the comments section of this blog).
If you are fortunate to find a mountain wadi that safely delivers you to around 1000 meters then you may notice another member of the subfamily, Glossonema varians. Apparently, they occur at lower altitudes, but I have only been fortunate to encounter them higher up. G. varians is unlike Desmodorchus, G. varians is not succulent but has branching annual stems from the base with broad, wavy-edged, almost triangular leaves with grey hairs. It is particularly attractive and has ellipsoid fruits with spines that harden when dry.
The mountains of the UAE are full of surprises with many other notable species. This makes a visit to the mountains an extremely rewarding experience for anybody interested in nature.
This account was written from numerous expeditions into the mountains of the UAE during my time as Senior Executive Officer of Sharjah Botanic Garden for His Highness Sultan bin Muhammad Al Qasimi, the Ruler of Sharjah.