A Northumberland Alpine Gardener's Diary
This entry: 27 February 2012 by John Richards
Tenerife again. Entry 207.
Back to Tenerife
Hardened readers may recall that we visited Tenerife for the first time two years ago, in January 2010, and I reported briefly on the visit in these pages (issue 138). That visit was not entirely successful, partly because our self-catering apartment was in Los Gigantes, a rather desolate (although scenically spectacular) resort in an area apparently devoid of shops. No sooner had we got there than the whole resort, ourselves included, succumbed to a particularly violent strain of norovirus, which put us out of action for several days. Our holiday concluded in even more spectacular form, as the resort received twice its annual rainfall (about 20 cm) in three days and was completely washed out. Luckily we went for two weeks, and in the interim were able to sample some of the many botanical wonders of the island.
During our travels we became aware that the north of the island had much more charm, and a good deal more botanical interest, than the drier south, and despite the greater chance of cool cloudy conditions and rain, we resolved to visit Puerto de la Cruz (which boasts two excellent botanic gardens and some interesting public parks, creditably decorated with endangered native plants) on any future visit.
So it was that we found ourselves in the excellent Hotel El Tope last week. The weather was indeed rather dull and cool, indeed no warmer than London most days, but we had a super time, especially botanically. Here is a view of the volcano El Teide which dominates the island, from the hotel balcony.
The Canary Islands are particularly fascinating to an evolutionary biologist as, like the Galapagos, they form a field laboratory which demonstrates evolution in rapid and spectacular action. The islands are of volcanic origin and only a few million years old, often much younger, and yet they boast several thousand species of plants. Tenerife itself has about 1500 species (about the same as the UK) in an area not much more than 1000 km square, and more than 80% of these are endemic to the islands, and more than 20% endemic to Tenerife. The other islands, although mostly smaller, have comparable levels of endemism, so that many genera show amazing adaptive radiation, so that in a number of genera one to several species have evolved to particular local niches on each of the main islands.
Although many genera show this island speciation, it has occurred to a remarkable extent in several genera, of which one might mention Aeonium, Limonium, Echium and Argyranthemum,each of which has at least 30 Canarian endemics.
I thought by way of illustration I would take species of a few of the more diverse genera by way of illustration. Aeonium is particularly attractive to rock gardeners because most are chasmophytes, living in crevices in cliffs or boulders, and they have very attractive forms of rosettes which are reminiscent of Sempervivums, or some saxifrages. Like most silver saxifrages, the rosette grows until it is big enough to flower, at which point a large inflorescence arises which eventually dies, killing off the rosette, although the plant is usually able to continue by way of offsets.
Having said this, these are dryland succulents of course, and most are probably not very hardy. I guess that some which live at altitudes of more than 1000 m, above Masca for instance, do probably experience light and occasional frosts, but they do so in dry conditions, and they would certainly not survive outside in any UK conditions, although I am sure they would do so in much of California, Australia, and other localities where rock gardeners live.
One of the interesting things about Tenerife in particular is the presence of relatively old mountain blocks at the north-eastern (Anaga) and north-western (Teno) extremities of the island. These are relatively humid areas, covered in parts with the old Tertiary laurel forest ('laurosilva'), and although they probably do not experience frost, it is likely that aeoniums from these areas would tolerate a higher level of rainfall in the garden.
I am showing rosettes rather than the rather unattractive flowering spikes, as it is in the former that most of the beauty lies. First a few of the larger species. Ae. holochrysum is widespread in the drier parts of the island and can stand two metres tall.
Ae. urbicum is another large species, although it tends to occur in wetter regions.
Ae. pseudurbicum is related to the latter, but tends to have narrower, more pointed leaves. It is restricted to drier parts of the north-west, for instance around the spectacular village of Masca which is particular rich in succulents such as Aeoniums and other Crassulaceae. The following picture shows the ridge on which Masca stands.
The round-leaved glaucous Ae. canariense is another common plant at Masca, growing here with Ae. holochrysum again.
Now for some more local species. Firstly, a trio from the north-eastern peninsula of the island, known collectively as Anaga. This area is highly forested, containing more intact ancient laurel forest than the rest, and is extremely spectacular, scenically. There is a goodish road along the top of the ridge east from Merceces, and this gives access to wonderful habitats and views. Here, first is what I take to be Ae. cuneatum which is one of the more localised north-eastern endemics. It is a relative of the more widespread Ae. canariense, but with leaves of another shape, and not so large.
Ae. ciliatum is another attractive species localised to the north-east of Tenerife. It has beautifully red-edged leaves with ciliate margins which are only obvious if you look closely.
Ae. lindleyi reaches the centre of the north coast, but is also a north-easterner. It is rather small and has much morte succulent leaves than most.
Some of the Aeoniums have many small rosettes which together form a low, cushion-shaped shrub of a form very familiar to alpine gardeners. One such is Ae. sedifolium which is common at Masca.
A rather more local westerner is Ae. haworthianum, another species which can be successful searched for around Masca.
I pictured the rarest of the Masca endemics, Ae. mascaense, back in 2010, but we did find it again. It is commonest above the road to the north of the village, although a little occurs by the terrace walk that connects different parts of the community.
Another lovely species that was pictured in 2010 is the extraordinarily symmetrical Ae. tabuliforme. This is best found on the cliffs above the road at El Fraile, in the far north-west corner of the island, although it is also to be found inland from Los Silos.
There are several other succulent genera in the Crassulaceae which show considerable endemic speciation on Canarian cliffs, and Greenovia is amongst these. In 2010 I pictured G. dodrentalis. This year we found fine colonies of Greenovia aurea on the edges of barrancas (seasonal torrent courses) beside the road up to Teide from the north. These occurred up to 1800 m, well into the frost zone, so this lovely species should be fairly hardy, if not damp tolerant.
If you ask why the Greenovia is not an Aeonium, well it differs in technical details of the flowers, for instance petal number.
Another genus which shows considerable diversity in the Canaries, and which I very much fell for, are the Pericallis. If this name seems unfamiliar, these plants used to be classified in Senecio and one or more species gave rise to the so-called cinerarias, popular pot-plants for the conservatory or cool greenhouse. If they are a bit gaudy in cultivation, the undeveloped wild plants have a grace and poise missing from their gross relatives. The commonest is Pericallis cruentus, which is common at about 800 m beside roads in the north-west of the island (Teno massif). It is a very variable plant, as the second photo shows, and this has no doubt led to the breeding of such a range of colours in capitivity.
P. tussiliaginis is a much smaller species from the north-east of the island. Its name recalls the coltsfoot, and the leaves are indeed very coltsfoot-like.
Abobe Masca we found a third species, P. lanatus. This forms a sprawling subshrub and is attractive, but it was only just coming into flower and none of the heads were quite open yet.
I am finishing with two genera of rather more interest to alpine gardeners, both of which form examples of another striking phenomenon, not fully explained, of oceanic islands, that is giantism; the occurrence of species far more robust than most of their mainland relatives. Possibly this is caused by plants evolving in the absence of large quadriped herbivores. The first such genus is Limonium, sea-lavenders. By no means all Canarian limoniums are halophytes (salt plants) and some are cliff plants from lush laurel forest zones. Those on Tenerife have now become extremely rare and endangered in the wild, but luckily they thrive in local gardens and parks where they are frequently cultivated, much to the merit of the Canary Islanders.
The best place to see Limonium arborescens in the wild are the sea-cliffs of El Fraile in the far north-west, west of Buenavista, where a few individuals can be seen close to the road.
L. fruticans is commoner in gardens than L. arborescens, but is almost extinct in the wild. It is a more robust, lush plant. A less well-known plant in gardens is L. macrophyllum from Anaga in the north-east which is very similar. However, it is possible to see another rather less robust species at El Fraile which is L. imbricatum with very bracteate inflorescences. This too would be an attractive subject if cultivated.
There is a third species evident below the El Fraile cliffs, but this one is a halophyte and is common on rocky shores throughout the islands. This is L. pectinatum.
The last genus I want to highlight is another, even more extreme example of giantism, that is Echium. Those of us fsamilar with Cornish coastal gardens, or those in the Mediterranean will be accustomed to giant vipers bugloss, of which the species most commonly grown, E. pininana is native to La Palma. However, Tenerife has some excellent examples too, one of which, E. giganteum is a common bush in the north which was featured in issue 138.
If you go up to the volcanic badlands on Teide at about 2000 m altitude you will see another spectacular species with huge spears of purple flowers, E. wildpretii. Sadly, this flowers in the summer, so I only have photos of mangy (and drought-stricken) rosettes.
Nevertheless, I was very struck by E. virescens which occurs by the road just south of Masca (at one of the few parking places on the scary road!).
A related species we saw on Anaga is the less spectacular E. strictum.
Finally, and back to the topic of locaised endemics again, E. leucophaeum only occurs on the hotter southern slopes of Anaga, where we found it difficult to approach closely.