Citrus L.

Tutin, T. G., Heywood, V. H., Burges, N. A., Moore, D. M., Valentine, D. H., Walters, S. M. & Webb, D. A., 1981, Flora Europaea. Volume 2. Rosaceae to Umbelliferae, Cambridge University Press : 229

4. Citrus L. 1

Small trees. Young twigs with single spines in the leaf-axils, but older branches often unarmed. Leaves alternate, simple, coriaceous, thin; lateral veins few. Petioles often more or less winged or margined and articulated with the lamina. Flowers white, solitary and axillary or in short axillary racemes. Sepals 4-5; petals (4-)5-(8). Stamens 4-10 times as many as the petals. Ovary usually 10- to 14-locular; ovules in 2 rows. Seeds surrounded by stipitate, fusiform pulp-vesicles.

Literature: W. T. Swingle, The Botany o f Citrus and its wild relatives, in H. J. Webber & L. D. Batchelor, The Citrus Industry 1: 129-474. Berkeley and Los Angeles. 1943. T. Tanaka, The species problem in Citrus (Revisio Aurantiacearum IX). Tokyo. 1954.

A genus of considerable taxonomic difficulty. The present account is based on the work of the above two authorities. The species described are those most commonly cultivated for their fruit and essential oils in the Mediterranean region. In addition, C. bergamia Risso & Poiteau , Hist. Nat. Orang. I l l (1818), is cultivated in Calabria for the essential oil yielded by its rind. It is a small tree with winged petioles and oblong-ovate leaves, and has a pale yellow, pyriform fruit 7-5-10 cm in diameter. All the cultivated species are probably derived from plants which are native in tropical and subtropical parts of S.E. Asia.

1 Petiole terete or carinate-margined but not winged; fruit 15-25 cm in diameter 1. medica 1 Petiole distinctly winged; fruit not more than 15 cm in diameter

2Stamens generally more than 4 times as many as the petals; flowers of two sorts, hermaphrodite and functionally male;

ripe fruit light yellow, with a mammilliform process at apex

3 Fruit acid; flowers tinged or streaked with purple 2. limon 3 Fruit insipidly sweet; flowers pure white 3. limetta 2 Stamens about 4 times as many as the petals; flowers usually

all hermaphrodite; fruit yellow or orange without a mamilliform process at apex

4 Leaves narrowly elliptical; fruit rarely more than 6-5 cm, depressed; rind very easily detached from the segments

4. deliciosa 4 Leaves broadly elliptical; fruit 7-15 cm, spherical or broadly ovoid, not or only slightly flattened above and below; rind adhering to the segments

5 Fruit 10-25 cm in diameter; rind yellow; petiole usually

broadly winged

6 Twigs and underside of midrib glabrous 5. paradisi 6 Twigs and underside of midrib sparsely hairy 6. grandis 5 Fruit usually 7-9 cm; rind orange or orange-yellow; petiole

rather narrowly winged, obovate to oblanceolate, usually

at least twice as long as wide

7 Fruit with a rough rind and bitter sour pulp; petioles

obovate in outline 7. aurantium 7 Fruit with a sweet taste and nearly smooth rind; petioles

oblanceolate in outline 8. sinensis