The micrantha is a wild

citrus ''Citrus'' is a genus of flowering trees and shrubs in the rue family, Rutaceae. Plants in the genus produce citrus fruits, including important crops such as oranges, lemons, grapefruits, pomelos, and limes. The genus ''Citrus'' is nativ ...

from the papeda group, native to southern

Philippines The Philippines (; fil, Pilipinas, links=no), officially the Republic of the Philippines ( fil, Republika ng Pilipinas, links=no), * bik, Republika kan Filipinas * ceb, Republika sa Pilipinas * cbk, República de Filipinas * hil, Republ ...

, particularly islands of

Cebu Cebu (; ceb, Sugbo), officially the Province of Cebu ( ceb, Lalawigan sa Sugbo; tl, Lalawigan ng Cebu; hil, Kapuroan sang Sugbo), is a province of the Philippines located in the Central Visayas region, and consists of a main island and 167 ...

and

Bohol Bohol (), officially the Province of Bohol ( ceb, Lalawigan sa Bohol; tl, Lalawigan ng Bohol), is an island province of the Philippines located in the Central Visayas region, consisting of the island itself and 75 minor surrounding islands. It ...

. Two varieties are recognized: small-flowered papeda (''C. hystrix'' var. ''micrantha''), locally known as ''biasong'', and small-fruited papeda (''C. hystrix'' var. ''microcarpa'') or ''samuyao''. Long viewed as a separate species, ''C. micrantha'', it is now generally viewed to fall within ''

Citrus hystrix ''Citrus hystrix'', called the kaffir lime or makrut lime, (, ) is a citrus fruit native to tropical Southeast Asia. Its fruit and leaves are used in Southeast Asian cuisine, and its essential oil is used in perfumery. Its rind and crushed leav ...

'', but genomic data on the latter is insufficient for a definitive conclusion. A micrantha was one of the

progenitor In genealogy, the progenitor (rarer: primogenitor; german: Stammvater or ''Ahnherr'') is the – sometimes legendary – founder of a family, line of descent, clan or tribe, noble house, or ethnic group.. Ebenda''Ahnherr:''"Stammvater eines G ...

species of some varieties of

lime Lime commonly refers to: * Lime (fruit), a green citrus fruit * Lime (material), inorganic materials containing calcium, usually calcium oxide or calcium hydroxide * Lime (color), a color between yellow and green Lime may also refer to: Botany ...

Description

The micrantha was first described to Western science in 1915 by Peter Jansen Wester, who worked for the Philippine Bureau of Agriculture at the time.

Biasong

Wester collected ripe fruit specimens of biasong (small-flowered papeda, ''Citrus hystrix'' var. ''micrantha'') on islands of Cebu, Bohol,

Dumaguete Dumaguete, officially the City of Dumaguete ( ceb, Dakbayan sa Dumaguete; fil, Lungsod ng Dumaguete), is a 3rd income class component city and the capital of the province of Negros Oriental, Philippines. According to the 2020 census, it has a ...

, Negros, and in the Zamboanga and Misamis provinces in

Mindanao Mindanao ( ) ( Jawi: مينداناو) is the second-largest island in the Philippines, after Luzon, and seventh-most populous island in the world. Located in the southern region of the archipelago, the island is part of an island group of ...

. The fruits were collected throughout the year, indicating that the plant is ever-bearing. Biasong is characterized by small flowers (thus the "small-flowered" moniker) with fewer

stamen The stamen (plural ''stamina'' or ''stamens'') is the pollen-producing reproductive organ of a flower. Collectively the stamens form the androecium., p. 10 Morphology and terminology A stamen typically consists of a stalk called the filame ...

s than other papedas and oblong-obovate, few-

locule A locule (plural locules) or loculus (plural loculi) (meaning "little place" in Latin) is a small cavity or compartment within an organ or part of an organism (animal, plant, or fungus). In angiosperms (flowering plants), the term ''locule'' usu ...

d fruits. Inhabitants did not use the fruits for food, but for hair-washing, and it had little economic importance. Biasong's aroma is similar to that of the samuyao variety of micrantha. The tree reaches in height. Leaves are long, wide, broadly elliptical to ovate,

crenate A leaf ( : leaves) is any of the principal appendages of a vascular plant stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, ...

, thin, with base rounded or broadly acute; apex acutely blunt pointed. Petioles are long, broadly winged, up to wide, with wings (phyllodes) sometimes larger than the leaf. Flowers are small, four-petaled, white with a thin purple edge, in diameter, forming

cymes An inflorescence is a group or cluster of flowers arranged on a stem that is composed of a main branch or a complicated arrangement of branches. Morphologically, it is the modified part of the shoot of seed plants where flowers are formed on ...

of two to five. There are 15 to 17 equal

s. The ovary is obovoid, with 6 to 8 slender, distinct

s. Fruits are

obovate The following is a list of terms which are used to describe leaf morphology in the description and taxonomy of plants. Leaves may be simple (a single leaf blade or lamina) or compound (with several leaflets). The edge of the leaf may be regular ...

to oblong-obovate, long, with diameter of , averaging in weight; their skin is rather thick, lemon-yellow, fairly smooth or with transverse corrugations; the pulp is juicy, grayish and acid, while juice cells are short and blunt to long, long, slender and pointed, sometimes containing a minute, greenish nucleus. They have numerous flat, pointed,

reticulate Reticulation is a net-like pattern, arrangement, or structure. Reticulation or Reticulated may refer to: * Reticulation (single-access key), a structure of an identification tree, where there are several possible routes to a correct identificat ...

seeds.

Samuyao

Wester collected ripe samuyao (small-fruited papeda, ''Citrus hystrix'' var. ''microcarpa'') fruit specimens from cultivation in Cebu and Bohol in June, and from November to February. Samuyao is rather smaller than biasong, with trees attaining 4.5 meters. It has small, thin leaves and flowers comparable in size to biasong. The fruit, 15–20 mm in diameter, is likely to be the smallest in the whole genus. Wester also recorded a somewhat more vigorous variety, called "samuyao-sa-amoo" in Bohol, with slightly larger fruits; there is a possibility that this species was actually ''Limonellus aurarius'', described by

Georg Eberhard Rumphius Georg Eberhard Rumphius (originally: Rumpf; baptized c. 1 November 1627 – 15 June 1702) was a German-born botanist employed by the Dutch East India Company in what is now eastern Indonesia, and is best known for his work ''Herbarium Amboinense ...

back in 1741 in a nearby area, although his description also fits a number of related species. Wester gave the botanical description: Clear, intensely fragrant oil can be produced from the samuyao peel, and it has been used as a hair fragrance by women who live where it grows.

Toxicity

The micrantha contains a significant amount of

bergapten Bergapten (5-methoxypsoralen) is a naturally-occurring organic chemical compound produced by numerous plant species, especially from the carrot family Apiaceae and the citrus family Rutaceae. For example, bergapten has been extracted from 24 ...

, a linear

furanocoumarin The furanocoumarins, or furocoumarins, are a class of organic chemical compounds produced by a variety of plants. Most of the plant species found to contain furanocoumarins belong to a handful of plant families. The families Apiaceae and Rutacea ...

well known for its phototoxic effects. Of 61 ''Citrus'' varieties tested, ''C. micrantha'' had the highest concentration of bergapten of any ''Citrus'' species. In particular, ''C. micrantha'' contained almost twice as much bergapten as the

bergamot orange ''Citrus bergamia'', the bergamot orange (pronounced ), is a fragrant citrus fruit the size of an orange, with a yellow or green color similar to a lime, depending on ripeness. Genetic research into the ancestral origins of extant citrus cultiv ...

whose essential oil is highly phototoxic. Indiscriminate use of

bergamot essential oil Bergamot essential oil is a cold-pressed essential oil produced by cells inside the rind of a bergamot orange fruit. It is a common flavoring and top note in perfumes. The scent of bergamot essential oil is similar to a sweet light orange peel o ...

has led to several cases of

phytophotodermatitis Phytophotodermatitis, also known as berloque dermatitis or margarita photodermatitis, is a cutaneous phototoxic inflammatory reaction resulting from contact with a light-sensitizing botanical agent followed by exposure to ultraviolet light (from t ...

, Cited i
CIR 2013
Cited i
CIR 2013
a potentially severe skin inflammation. In these cases, the primary causal agent is believed to be bergapten.

Hybrids

The

Key lime The Key lime or acid lime (''Citrus'' × ''aurantiifolia'' or ''C. aurantifolia'') is a citrus hybrid ('' C. hystrix'' × '' C. medica'') native to tropical Southeast Asia. It has a spherical fruit, in diameter. The Key lime is usually picked ...

(''Citrus aurantifolia'') is a hybrid of the micrantha and the citron. It, in turn, has been crossed with a lemon to produce the

Persian lime Persian lime (''Citrus'' × ''latifolia''), also known by other common names such as seedless lime, Bearss lime and Tahiti lime, is a citrus fruit species of hybrid origin, known only in cultivation. The Persian lime is a triploid cross betwee ...

(''C. latifolia''). There are lumias that are distinct micrantha/citron hybrids, such as the Pomme d'Adam, while other lumias, like the Borneo lemons, are micrantha/citron/pomelo tri-species hybrids. An Indonesian hybrid, the nansaran (''C. amblycarpa''), is a ''C. hystrix''/''C. reticulata'' cross.

References

External links

Searching for the Elusive Samuyao
"Our Philippine Trees" blog

"Our Philippine Trees" blog {{Taxonbar, from=Q20704151 Micrantha Flora of the Philippines Plants described in 1915