The garden’s unique lichen collection was renewed, with samples collected from various desert habitats, representing the variety of lichen species from the arid region of Israel. This live collection is the only one of its kind in Israel and one of the few in the world. The lichen collection was established by the previous director of the garden, Prof. Jacob Garty, who still continues his research on the taxonomy and ecology of the lichen species of Israel. Lichens are a classic example of tight mutualism: an organism composed of two different organisms, living in cooperation and completely dependent on one another (symbiosis). Lichens comprise an alga and a fungus, and their symbiotic relationship enables the lichens to grow even in the harshest habitats on earth, such as in deserts, atop tall mountains and near the poles. The fungus establishes itself in the substrate, creating a protective layer against dehydration and solar radiation and comprises the bulk of the lichen. The alga, protected within the layers of the fungus, produces energy (sugar) by photosynthesis, as in any other plant. The evolution of this successful combination, which took place many eons ago, has proven to be so successful that it continues to exist today. In contrast to plants, the lichen thallus lacks protective layers, making it permeable to air pollutants. Consequently, lichens are good bioindicators for detecting air pollution, offering a warning sign for humans. Unfortunately, for this very reason many lichen species in the botanical garden do not last long in the polluted air conditions of Tel Aviv near the Ayalon highway, and the collection must be renewed every few years. Last week fresh individuals of Ramalina maciformis, Caloplaca ehrenbergii and Guellia canescens, all species growing on flint rock, were added to the collection in the Garden. Some endolithic lichens are also present in the collection, growing in limestone. These lichens actually grow inside the rock, near to its surface.

Photo: Gavri Sion

Caloplaca ehrenbergii, Photo: Gavri Sion

Photo: Or-Leyl Har-Edom

Endolithic lichens, Photo: Or-Leyl Har-Edom