Bitter orange (Seville orange) — Citrus × aurantium

Small citrus tree and fruit valued for bitter peel and blossoms; used in marmalade, liqueurs, perfumes, and as a rootstock. Scientific name Citrus × aurantium, a pomelo–mandarin hybrid.

Bitter orange, often called the Seville or marmalade orange, is the fruit and tree of Citrus × aurantium. It is a cultivated citrus notable for its thick, aromatic rind and distinctly bitter pulp. Botanically the plant is a naturally occurring hybrid between the larger pomelo and the smaller mandarin, a lineage that traces back to Asian origins and later spread into the Mediterranean.

Characteristics

The tree is small to medium in size, with fragrant white flowers and glossy leaves. Fruit are round to slightly oblong, typically orange to deep orange when ripe, and contain high levels of pectin in the peel. The flesh is sour and bitter rather than sweet, due to compounds such as limonoids and certain flavonoids; the peel and flowers yield essential oils with distinctive aromas used in flavoring and perfumery.

History and cultivation

Bitter orange has a long history of cultivation around the Mediterranean and parts of Asia. It became especially associated with Seville, Spain, where its bitter fruit was widely processed into preserves. The tree adapts to temperate climates and is grown for both fruit and as a hardy rootstock to support sweeter citrus varieties.

Uses

Marmalade and preserves: the high pectin content and tart flavour make it prized for traditional marmalade.
Flavoring and liqueurs: peel oils and extracts contribute to some classic liqueurs and liquors.
Perfume and aromatics: orange blossom yields neroli oil; leaves and twigs produce petitgrain-type aroma compounds.
Horticulture: used as grafting rootstock to improve cold tolerance and disease resistance in commercial citrus.

While valued for culinary and aromatic qualities, bitter orange extracts have been used in traditional remedies and contemporary supplements; such uses warrant caution because certain constituents can interact with medications or affect cardiovascular function in some people. Distinct from the sweet orange (the common eating orange), the Seville or bitter orange remains important where its bitterness and aromatic oils are specifically desired.