Olive Tree

Appearance

The olive tree, "Olea europaea", is an evergreen tree or shrub native to the Mediterranean, Asia and Africa. It is short and squat, and rarely exceeds 8–15 m in height. However, the "Pisciottana", a unique variety comprising 40,000 trees found only in the area around Pisciotta in the Campania region of southern Italy often exceeds this, with correspondingly large trunk diameters. The silvery green leaves are oblong, measuring 4–10 cm long and 1–3 cm wide. The trunk is typically gnarled and twisted.

The small white, feathery flowers, with ten-cleft calyx and corolla, two stamens and bifid stigma, are borne generally on the previous year's wood, in racemes springing from the axils of the leaves.

The fruit is a small drupe 1–2.5 cm long, thinner-fleshed and smaller in wild plants than in orchard cultivars. Olives are harvested in the green to purple stage. Canned black olives may contain chemicals that artificially turn them black. "Olea europaea" contains a seed commonly referred to in American English as a pit or a rock, and in British English as a stone.

Naming

There are six natural subspecies of Olea europaea distributed over a wide range:

Olea europaea subsp. europaea (Mediterranean Basin)
Olea europaea subsp. cuspidata (from South Africa throughout East Africa, Arabia to South West China)
Olea europaea subsp. guanchica (Canaries)
Olea europaea subsp. cerasiformis (Madeira)
Olea europaea subsp. maroccana Morocco
Olea europaea subsp. laperrinei (Algeria, Sudan, Niger)
The subspecies maroccana and cerasiformis are respectively hexaploid and tetraploid.

Wild growing forms of the olive are sometimes treated as the species Olea oleaster.

Distribution

Since its first domestication, "Olea europaea" has been spreading back to the wild from planted groves. Its original wild populations in southern Europe have been largely swamped by feral plants.

In some other parts of the world where it has been introduced, most notably South Australia, the olive has become a major woody weed that displaces native vegetation. In South Australia, its seeds are spread by the introduced red fox and by many bird species, including the European starling and the native emu, into woodlands, where they germinate and eventually form a dense canopy that prevents regeneration of native trees. As the climate of South Australia is very dry and bushfire prone, the oil rich feral olive tree substantially increases the fire hazard of native sclerophyll woodlands.

Evolution

The edible olive has been cultivated for at least 5,000 to 6,000 years, with the most ancient evidence of olive cultivation having been found in Syria, Palestine and Crete. The olive tree is native to the Mediterranean region and Western Asia, and spread to nearby countries from there.

The immediate ancestry of the cultivated olive is unknown. It is assumed that "Olea europaea" may have arisen from "O. chrysophylla" in northern tropical Africa and that it was introduced into the countries of the Mediterranean Basin via Egypt and then Crete or the Levant, Syria, Tunisia and Asia Minor. Fossil Olea pollen has been found in Macedonia, Greece, and other places around the Mediterranean, indicating that this genus is an original element of the Mediterranean flora. Fossilized leaves of Olea were found in the palaeosols of the volcanic Greek island of Santorini and were dated about 37,000 BP. Imprints of larvae of olive whitefly "Aleurolobus olivinus" were found on the leaves. The same insect is commonly found today on olive leaves, showing that the plant-animal co-evolutionary relations have not changed since that time.

As far back as 3000 BC, olives were grown commercially in Crete; they may have been the source of the wealth of the Minoan civilization.

Uses

The olive tree, "Olea europaea", has been cultivated for olive oil, fine wood, olive leaf, and the olive fruit. 90% of all harvested olives are turned in to oil, while about 10% are used as table olives.

Cultural

Olive oil has long been considered sacred. The olive branch was often a symbol of abundance, glory and peace. The leafy branches of the olive tree were ritually offered to deities and powerful figures as emblems of benediction and purification, and they were used to crown the victors of friendly games and bloody wars. Today, olive oil is still used in many religious ceremonies. Over the years, the olive has been the symbol of peace, wisdom, glory, fertility, power and purity.