Kaffir Lime

Although apparently native to S China into SE Asia and Malesia, the natural distribution of this species is obscured by cultivation. Selected forms are cultivated throughout the warm parts of the world for their culinary (leaves) and medicinal (fruit) uses. All named taxa (save perhaps some from central Malesia) seem to have been based on cultivated plants as discussed by Mabberley (Gard. Bull. Singapore 54: 173-184. 2002). Commonly seen in China are cultivated plants (the "lime leaves" of commerce) with the following characteristics: leaf blade broadly elliptic, apex obtuse to rounded; fruit subglobose, ca. 4 × 3.5 cm, smooth, apex with a papilla; pericarp ca. 2 mm thick; sarcocarp in 6 or 7 segments, 6-8-seeded but 1 or 2 seeds undeveloped; seeds pyramidal, 1.5-1.8 × 1-1.4 cm, 0.8-1.2 mm thick, with alveolate ridges.

Trees 3-6 m tall. Branchlets with spines. Leaves dark red when young; petiole winged, apex rounded to truncate; leaf blade ovate, 5-8 × 2.5-4.5 cm, 1-2.5 cm longer (rarely same length) and 0.5-1 cm wider than winged petiole, tertiary veins conspicuous, margin apically conspicuously and sparsely crenate, apex narrowly obtuse. Inflorescences with (1 or)3-5 flowers; peduncle 1-5 mm. Flower buds globose. Calyx lobes 4 or 5, broadly triangular, ca. 4 × 6 mm. Petals white but pinkish red outside, 7-10 mm. Stamens ca. 30; filaments distinct. Style short, thick. Fruit lemon yellow, ellipsoid to subglobose, 5-7 × 3-5 cm, slightly coarse or smooth, oil dots numerous and prominent, apex rounded; pericarp thick; sarcocarp in 11-13 segments, very acidic and slightly bitter. Seeds numerous 1.5-1.8 × 1-1.2 cm, ridged; embryo solitary; cotyledons milky white. Fl. Mar-May, fr. Nov-Dec.

N Guangxi, Yunnan [Indonesia, Myanmar, New Guinea, Philippines, Thailand].

Citrus auraria Michel; C. echinata Saint-Lager; C. hyalopulpa Tanaka; C. kerrii (Swingle) Tanaka; C. macroptera Montrouzier var. kerrii Swingle; C. papeda Miquel; Fortunella sagittifolia F. M. Feng & P. I Mao; Papeda rumphii Hasskarl.

Citrus hystrix., the Kaffir or makrut lime or papeda, is a small tree in the Papeda subgenus of the Rutaceae (citrus family). Members of this subgenus are characterized by fruits that are inedible, even when ripe, and contain acrid oil droplets in the juice vesicles (pulp cells). Thus, this species is used primarily for its leaves, which are used fresh or dried as an herb to flavor Asian dishes, including soups, stews, curries, and sauces. It is common in the cuisine of Thailand, and provides the characteristic flavor of tom yam soup. The zest and rind may also be used, but the fruit itself has almost no juice, and is primarily used for traditional medicinal purposes. (The lime that is sold fresh or for its juice is from related species, including C. aurantiifolia., the key lime, and C. latifolia, the Persian or Tahitian lime.) C. hystrix typically grows 3 to 6 m (9.75 to 19.5 ft) tall. The aromatic leaves, which are evergreen, have a distinctive structure, with a winged petiole (leaf stem) that is similar in size to the leaf itself, giving the appearance a laterally divided leaf. The globose flower buds open into fragrant flowers with 4 to 5 petals and around 30 stamens; petals are white with reddish or pink on the outside. The sub-globose to ellipsoid fruit is small, from 3 to 5 cm (1 to 2 in) wide by 5 to 7 cm (2 to 3 in) long--similar in size to slightly larger than a kumquat--with a rough skin with numerous small oil glands, and ripens to lemon yellow. C. hystrix originated in southeast Asia, but its precise native range has been obscured by a long history of cultivation, along with hybridization. The species and its various hybrids are now cultivated widely throughout the region, from Sri Lanka east to the Phillipines. (Flora of China 2012, van Wyk 2005)

Celebes papeda, is a citrus that grows in the northeastern Celebes and the southern Philippines. Under some taxonomic systems it is named Citrus celebica, else is a regional variant of Citrus hystrix. It is a small tree with inedible fruit.