The Phyto-Philes: Dragon Tree
Created | Updated Dec 21, 2014
The Canary Islands Dragon Tree
Willem is a wildlife artist based in South Africa. He says "My aim is simply to express the beauty and wonder that is in Nature, and to heighten people's appreciation of plants, animals and the wilderness. Not everything I paint is African! Though I've never been there, I'm also fascinated by Asia and I've done paintings of Asian rhinos and birds as well. I may in future do some of European, Australian and American species too. I'm fascinated by wild things from all over the world! I mainly paint in watercolours. . . but actually many media including 'digital' paintings with the computer!"
This time I bring you one of the most surreal-looking plants in the world. This is the Canary Islands Dragon Tree, Dracaena draco. While we have dragon trees in South Africa as well, our species are nowhere near as big or impressive as their Canary Islands relative. This species also occurs in the Cape Verde Islands, the Azores and Madeira, these also being off the coast of northwest Africa. It has also been found on the African continent, in Morocco. The great dragon tree is perhaps a remnant of subtropical forests that once covered much of North Africa, but retreated during the recent aridification that produced the Sahara Desert. Similar, related species are found in northeast Africa, and on the island of Socotra (which I hope to feature numerous more times here). Other, less impressive (but still fascinating) species of dragon tree are found in the moister parts of sub-Saharan Africa as well as in Asia, and on Indian Ocean islands like the Mascarenes. There's one species in tropical America. The Sansevierias are close relatives.
A Vegetable Dragon
The dragon tree has a very unique, craggy appearance. It consists of a trunk branching into individual branches, each tipped with a crown of leaf rosettes, the leaves being long, fibrous, tough and spiky. The trunk is not conventionally woody like that of a normal tree, but fibrous and pulpy. This species is in fact one of only a few monocotyledonous (= having a single seed leaf) plants that grow to tree size. The only monocots that as a matter of routine reach tree size are the palms. The dragon tree is not a palm. It is in fact more closely related to asparagus plants! It belongs to a group of asparagaceous plants that are very big and robust, many growing into stoutly-trunked trees. Of those, it is the largest. Dragon trees can exceed 20 m/67' in height, with a trunk circumference (NOT diameter!) of about the same. This means the trunk would be five to six metres/yards wide at ground level. I often see confusion in sources between circumference and diameter. If you remember that pi comes to a bit more than three, you can work out that a tree's circumference (total measurement around the trunk) would come to about three times its average diameter (width of the trunk). Tree trunks are never perfectly circular in cross section, so this is a rough but relatively dependable guideline.
The dragon tree's weird shape comes from its unique way of growth. A young dragon tree has an unbranched trunk bearing a single crown of leaves. When it reaches the age of about 10 to 15 years, it flowers for the first time. The inflorescence is a large branched structure emerging from the centre of the leaf rosette, bearing many individual small white flowers. After flowering, each pollinated flower is replaced by a red berry. Then when all the berries have fallen or have been eaten by birds, the inflorescence itself also detaches. Now, at the tip of the crown of leaves, new growth buds develop. Each of these develops into a separate crown and so from the first original crown, several new, separate branches grow. These keep growing for another 10-15 years, and then the tree flowers again, each crown bearing an inflorescence, and each afterwards again branching into new crowns. And so it goes on. If a tree grows uniformly, it is therefore possible to identify the 'branching events' along its crown, which also gives an indication of its age. (Because of its pulpy wood, it lacks growth rings.)
The Thousand-Year Dragon
In the wild, tree crowns may not be very uniform, since they might suffer damage on one side or another distorting the regular pattern of growth. But often, they are. The largest surviving dragon tree is one called 'El Drago Milenario' ('The Thousand-Year-Old Dragon') which grows at Icod de los Vinos on the island of Tenerife. It is about seventeen metres tall with a trunk about five metres wide, with a very intricately branched crown. Tradition alleges that this tree is several thousand years old. But its crown is fairly regularly and symmetrically branched, and according to the above 'system' of branching, indicates that this tree is probably not much more than three hundred years old. Still, it is a most impressive specimen!
Dragon's Blood
This tree is also a source of what is called 'dragon's blood'. This is a deep red resin that exudes from any wounds made in the tree's bark or leaves. It has been used as medicine, being said to cure intestinal and respiratory complaints, and also as a paint pigment and for dyeing, such as staining the wood from which Stradivarius' violins were made.
Vanished Forests and Island Endemism
The Canary Island Dragon Tree illustrates some very interesting ecological principles. Growing mostly on a range of islands off the African coast, it shows an example of something called island endemism. That means things are, in the wild, only found on certain islands. The Canary Islands indeed have many plant species that grow only there, nowhere else. In the dragon tree's case, it probably once was found over much of North Africa, as the remnant in Morocco indicates, but has almost completely died out there as the climate became too arid. But the Canary Islands, situated where ocean currents bring moist air towards them, receive somewhat more rain, especially in the mountainous interior, and so these trees can still survive there.
The native forests and plants of the Canary Islands form a kind of floral 'province' shared with the Azores, Madeira and the Cape Verde Islands. This is called the Macaronesian floristic region. It is characterized by sub-tropical forests dominated by trees in the laurel family. But there are many other kinds of unique tree and plant associated with them. Today, almost all of the original forests have been destroyed by humans. It is probable that this kind of forest was once widespread, found over north Africa and southern Europe, responding to the fluctuations of the ice ages, moving northward as the climate warmed, and southward as it cooled. But recent factors led to a massive drying-out of North Africa, forming the Sahara Desert; only along the coast of the Mediterranean are climates still moist enough for forests, and today these are similar to the Mediterranean forests of southern Europe, from where the majority of the plants were able to spread southward in response to the warming since the latest period of glaciation. So, only on those islands, where the typical North European plants were unable to invade, do those original subtropical forests still exist, even if just a tiny remnant.
There are many instances of plant and animal species that have died out over much of their earlier ranges but survive on small islands because of local factors giving them protection. In the case of animals, islands may be devoid of large predators, and so they can survive there. Birds on predator-free islands often lose the ability to fly.
Also, on islands, animals and plants can evolve differently from how they evolve on the mainland. The very fact that an island is an island, isolated by stretches of ocean water, make them little self-contained worlds with their own individual histories. So, on islands, new species evolve, species very unique, and indeed, islands develop their own unique landscapes and animal and plant 'societies'. The Canary Islands have many other species unique to them, as well as populations of species found elsewhere, but starting to become distinct, so that the Canary Island populations are considered to be separate sub-species. These island populations not only look different, but also behave differently.
Unfortunately, these unique island plant and animal societies are also very fragile and sensitive to disturbance. Evolving in isolation, in relatively small, closed-off little 'worlds', they are not as robust as the huge populations that can be sustained by continents like Africa itself. Especially the coming of humans have caused massive disruptions to island ecosystems. A great many animal species have gone extinct, including large numbers of flightless birds, but plants have also been hit hard. Many of the Canary Islands' unique plant species are endangered today; the humans have replaced them with their crops and with plants brought from Europe and elsewhere, and introduced goats and other browsers the native plants never before had to contend with. But today, at least, people in the Canary Islands are starting to recognize the uniqueness and preciousness of their plant heritage, and are starting with projects to protect and propagate them.
