The micrantha is a wild

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

from the papeda group, native to southern

Philippines The Philippines, officially the Republic of the Philippines, is an Archipelagic state, archipelagic country in Southeast Asia. Located in the western Pacific Ocean, it consists of List of islands of the Philippines, 7,641 islands, with a tot ...

, particularly islands of Cebu and

Bohol Bohol (), officially the Province of Bohol (; ), is an island province of the Philippines located in the Central Visayas Regions of the Philippines, region, consisting of the island itself and 75 minor surrounding islands. It is home to Bohola ...

. 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''. Although long viewed as a separate species, ''C. micrantha'', it is now generally viewed to fall within '' Citrus hystrix'', but genomic data on the latter is insufficient for a definitive conclusion. A micrantha was one of the progenitor species of some varieties of lime.

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, Negros, and in the Zamboanga and Misamis provinces in

Mindanao Mindanao ( ) is the List of islands of the Philippines, second-largest island in the Philippines, after Luzon, and List of islands by population, seventh-most populous island in the world. Located in the southern region of the archipelago, the ...

. 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 (: stamina or stamens) is a part consisting of the male reproductive organs of a flower. Collectively, the stamens form the androecium., p. 10 Morphology and terminology A stamen typically consists of a stalk called the filament ...

s than other papedas and oblong-obovate, few- loculed fruits. Though the fruit is not eaten and with little economic importance, its juice is used as a souring agent for kinilaw, or for hair-washing. 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 Ovate may refer to: * Ovate (egg-shaped) leaves, tepals, or other botanical parts *Ovate, a type of prehistoric stone hand axe * Ovates, one of three ranks of membership in the Welsh Gorsedd * Vates or ovate, a term for ancient Celtic bards ...

, crenate, 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 of two to five. There are 15 to 17 equal

s. The ovary is obovoid, with 6 to 8 slender, distinct locules. Fruits are obovate 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 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 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 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 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 flavouring and top note in perfumes. The scent of bergamot essential oil is similar to a sweet light orange pe ...

has led to several cases of

phytophotodermatitis Phytophotodermatitis, also known as berloque dermatitis,, margarita photodermatitis,, lime disease or lime phytodermatitis is a cutaneous phototoxic inflammatory reaction resulting from contact with a light-sensitizing botanical agent (such as ...

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

Hybrids

The Key lime (''Citrus aurantifolia'') is a hybrid of the micrantha and the citron. It, in turn, has been crossed with a

lemon The lemon (''Citrus'' × ''limon'') is a species of small evergreen tree in the ''Citrus'' genus of the flowering plant family Rutaceae. A true lemon is a hybrid of the citron and the bitter orange. Its origins are uncertain, but some ...

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 betwe ...

(''C. latifolia''). There are lumias that are distinct micrantha/citron hybrids, such as the Pomme d'Adam, while other lumias, like the

Borneo Borneo () is the List of islands by area, third-largest island in the world, with an area of , and population of 23,053,723 (2020 national censuses). Situated at the geographic centre of Maritime Southeast Asia, it is one of the Greater Sunda ...

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