JBS - itineraries (summer)

Towards the end of May, at the onset of summer, the majority of plants in the Soller Botanic Garden begin a period of adaptation to lack of rain, and this gives the Garden a new and distinctive look. This is a natural process for Mediterranean vegetation.

The Mediterranean flora evolved from temperate and tropical species; this began in the Pleistocene age about 2 million years ago.

Since then, drought and summer heat have been the characteristic of Mediterranean climates. Indeed, in addition to the lands in and around the Mediterranean basin, there are other places in the world which share a Mediterranean climate. Such are California, central Chile, the Cape region of South Africa, and Southern Australia.

Naturally, under dry summer conditions, animals and plants must avoid loss of water for their survival, whilst using a minimum amount of energy.

Native Mediterranean plants have adapted perfectly to such hardships. In the Botanical Garden, you can now view this singularity with its typical features.

By following the itineraries in this pamphlet you will begin to understand how our own native plants have adapted to the summer season.

Following the Garden plan as seen in the leaflet provided, the itineraries corresponds to areas M1-M2-M3-M4-M5.

The plan and itineraries are just a guideline. Please refer to the plant labels which, give both the scientific and local names of individual plants in each area, as shown in the Soller Botanic map.

Towards the end of spring the dry season sets in. Plants, like animals, have adapted to the two distinctive factors of the Mediterranean climate throughout the summer; heat and drought.

They reduce activity to a minimum and during adverse times, maintaining a latent existence. For example, as bulbs underground. Others, such as annuals, which have already flowered and borne fruit during spring, spend the summer as seeds, waiting for the first rain in autumn or until it does rain the following spring.
They modify their morphology to make themselves resistant to summer conditions. Either by
- Reduction of foliar mass to avoid excessive transpiration. Or
- Control of transpiration:
- - Protecting the stomates and regulating its aperture and closure. The stomates (pores) are openings found on leaf surfaces, through which they absorb air.
  - Producing substances, which can be volatile, oleaginous and sometimes toxic, forming a waterproof surface, which impedes internal fluid evaporation. Plants can protect themselves from thirsty herbivores by excreting toxic substances that coat the surface of the succulent green leaves.

These plants have adopted a cushion like, semi-spherical shape, which allows them to maintain a lower temperature and a significantly cooler micro-climate within the cushion, where they suffer less than outer parts exposed to the sun. Another characteristic of these plants is their foliar reduction, hence decreasing transpiration. The presence of spines is common and of great defensive value against herbivores. There are two types of spines. One is formed by the rachis or axis of the leaves once the folioles have fallen, as is the case in the Astragalus balearicus. The other uses the stalks, once the leaves have fallen, as in Launaea cervicornis and Femeniasia balearica.

If you look carefully you will see that the "spines" of these cushion like plants, are not really spines, as in the roses, but rather leaves or stalks that have gone through a process of transformation.

At the Botanic Garden you will find that a plastic ring surrounds bulbous plants. Lack of water at the onset of the dry season causes green leaves to dry out completely. The plants only survive underground as a bulb, rhizome, or corm, where all necessary nutrients are accumulated. Shortly after the first rain in the following autumn or spring, according to the species, the leaves and flowers will re-emerge again.

Heather leaves are very small and almost cylindrical. This diminished surface of the leaves, allows the plant to perform photosynthesis whilst minimizing loss of water through the leaf’s surface.

Box is a good example of sclerophyllous vegetation. The leaves are leathery and green through out the year. The leathery texture allows stomates to open and close without their tissues being broken. This way the plant controls transpiration according to the surrounding humidity and temperature, hence avoiding the loss of moisture.

The evergreen oak is, perhaps, the most typical tree of the Mediterranean. It controls transpiration through its leaves. The leaf’s upper part is leathery so it does not shrivel if it lacks water, and the underside is covered with hairs, thus avoiding excessive transpiration. This system helps sustain a more humid microclimate around the transpiring cells or stomates.

In the old days, this type of Jerusalem Sage was used to make the wick for the traditional oil lamps. Its leaves are completely covered by hairs which protect it from loss of moisture through transpiration. They also reflect light, as do so many other silvery Mediterranean plants.

Rosmary has linear leaves with curled up edges that help control transpiration. They also contain volatile substances, which help reduce excessive moisture loss, and discourage thirsty herbivore depredation.

The pink flowered White Rock-rose is highly inflammable, but the fire hazard becomes a benefit for this bush. Fires quickly activate the germination of its seeds. Its roots grow rapidly in spring when water is available, and they spread across the surface of the ground to make the most of any rainwater before it evaporates. In summer, its leaves, which are covered with a dense white hair to protect its transpiration cells from losing water, wrinkle and loose their turgidity until the plant receives water again. These plants with marcarescent leaves, which are soft and reversibly decaying during the dry season, are called malacophyles.

The balearic St John’s Wort has green leaves throughout the year. It flowers in the more favourable seasons, in spring and autumn. It has glands on its leaves, which can be seen against the light. These glands contain an oily substance, which helps to reduce the transpiration during summer by forming an impermeable layer of ethereal oils, which in turn help maintain the pressure of the water vapour and thus avoiding evaporation.

The chamomiles, each variety or species of which has a different shade of silvery grey, are typical Mediterranean plants. Their characteristic smell indicates the presence of volatile compounds, which help to control the transpiration, and which in turn maintain a more or less constant water vapour pressure.

The locally called Stinky Wild Parsnip, Stink-grass or Infernal Fig-tree, has a thick rhizome like a carrot, which serves as a water reservoir during the dry season. Its shiny leaves, from which derives the scientific term lucida have a waxy covering which protect it from and excessive transpiration. It has a foetid smell due to the volatile compounds that helps protect it from being eaten by herbivore animals.

The Tree Spurge, as all spurges, has a white latex which can give you a sort of nettle rash. In summer it loses almost all of its leaves. It accumulates water in its remaining tissues. When the first autumn rains arrive, it re-sprouts. Its splendid lime green foliage add colour to the Mediterranean scenery.

During the summer this plant loses its minute leaves and carries out photosynthesis through its green stems.

Leaves are totally absent in this plant. It transpires through its stems, which are also spiny in order to defend it against possible herbivore depredators.

In conclusion, one way or another, the plants of the Mediterranean get through the summer with low metabolic activity, in expectation of the cool rains of autumn; for them these represent a new spring.

Visit the Soller Botanical Garden in autumn, locally known as the ‘Winter Spring’ or ‘Second Spring’, when plants awake from their long summer slumber. Then will you see our plants covered once more with young leaves and the first flowers.