Olives, ash trees, lilac and jasmine all belong to one ancient family
The tree that gives us olive oil, the ash prized for tough timber, and garden favourites such as lilac, forsythia and privet are all cousins. The olive family, Oleaceae, stretches from the subarctic to the southern tips of Africa, Australia and South America, and its flowers betray the kinship with just two stamens.
Oleaceae is a family of woody plants, mostly trees and shrubs with a few climbing lianas, in the order Lamiales. It currently counts 28 genera, one recently extinct; one genus, Cartrema, was revived in 2012. Species estimates run from about 600 to 900, and most of the uncertainty comes from jasmine alone, for which botanists accept anywhere between 200 and 450 species. The olive genus, Olea, gives the family its name.
The key identifying trait is in the flower. Blooms are usually symmetrical, often abundant and strongly scented, yet the stamens are reduced to two, a combination shared only with the sister family Carlemanniaceae. Leaves grow opposite one another, with rare exceptions such as some jasmines arranged in a spiral, and evergreen species dominate in warm regions while deciduous ones dominate colder places. Fruits vary widely: berries, stone fruits, capsules or winged samaras. Birds spread most berry-bearing species, and the wind carries the samaras.
The family's centres of diversity are Southeast Asia and Australia, with many species also in Africa, China and North America, and tropical members range from dry lowland forest to cloud forest on mountains. Although fossils are sparse and molecular dating is imprecise, it is clearly an ancient group that spread widely early on. Some genera appear to be relicts, isolated on mountaintops by surrounding lowlands and little changed for long periods.
Classification is still shifting. There are no subfamilies, but five tribes have strong molecular support, and how they relate was only worked out in 2014. Several genera have turned out to be polyphyletic, so genus counts will change. Economically the family punches above its weight: olives for fruit and oil, ash for wood, a range of ornamentals, and at least two jasmines that yield an essential oil and flowers added to tea.
Source: Oleaceae
