The Oleaceae family counts ca. 24 genera and 800 species and is almost (sub-) cosmopolitan, with a higher concentration of species in Asia (Mabberley 2008). In Belgium only two genera are originally native, Fraxinus and Ligustrum, each with a single native species (respectively Fraxinus excelsior L. and Ligustrum vulgare L.; Lambinon & Verloove 2012). However, many species of the Oleaceae family are cultivated as ornamentals and some have been recorded as escapes in Belgium. In addition to those included in this account, species of Osmanthus are sometimes encountered in old parks, cemeteries, etc., especially O. heterophyllus (G. Don) P.S. Green and O. ×burkwoodii (Burkwood & Skipwith) P.S.Green, the latter being a hybrid of O. decorus Kasapligil and O. delavayi Franchet.
Additional information on the family is available at the Oleaceae Information site at: http://www.oleaceae.info/.
1 Leaves pinnately compound (rarely reduced to a single leaflet). Fruit a samara. Flowers inconspicuous, petals either lacking or minute === Fraxinus
Leaves simple to trifoliolate. Fruit a capsule or a berry. Flowers conspicuous, petals always present and obvious === 2
2 Flowers yellow, appearing before the leaves === 3
Flowers white or lilac-pink, never yellow, appearing after the leaves === 4
3 Flowering starts in spring. Fruit a dry capsule. Leaves usually simple, rarely with three unequal leaflets. Twigs hollow or with interrupted pith === Forsythia
Flowering starts in late autumn-winter. Fruit a berry. Leaves ternate, with three equal leaflets. Twigs solid === Jasminum
4 Fruit a berry. Corolla always white. Leaves persisting to deciduous === Ligustrum
Fruit a dry capsule. Corolla lilac-pink (white in cultivars only). Leaves deciduous === Syringa
Lambinon J. & Verloove F. (2012) Nouvelle Flore de la Belgique, du Grand-Duché de Luxembourg, du Nord de la France et des Régions voisines (Ptéridophytes et Spermatophytes). Sixième édition. Jardin botanique national de Belgique, Meise: CXXXIX + 1195 p.
Mabberley D.J. (2008) Mabberley’s plant-book (3th ed.). Cambridge University Press, Cambridge: XVIII + 1021 p.
Wallander E. & Albert V.A. (2000) Phylogeny and classification of Oleaceae based on rps16 and trnL-F sequence data. Amer. J. Bot. 87: 1827-1841. [available online at: http://www.oleaceae.info/publications/Wallander-Albert-2000.pdf]