Archidendron bubalinum

A small unarmed tree with grey bark that grows up to 20-25 m in height,^[8] with a trunk that can reach upwards to 25 m in diameter.^[9] The branchlets are terete reddish to light brown when dry, with a rusty puberulous to glabrescent outermost layer that scales off.^[10]

Leaves alternate, pinnate^[7] and green when mature. The rachis is 0.5-4(-6) cm, with a gland or extrafloral nectary present^[11] below the junction of the petiolules. Leaflets are soft, elliptic to ovate-elliptic in shape, approximately 6-16 cm long by 3-8 cm wide, have 1-2 pairs per pinna, chartaceous (thin and papery), and supported by a petiolule. Both the surfaces of the leaflet are glabrous (hairless), main vein is central or nearly central, with the lateral veins being prominulous (protruding slightly) on both surfaces.^[10] Young leaflet shoots are dark purple in colour, slowly transitioning to green or dark green as they mature.^[12]

Trees produce fragrant paniculate inflorescences, usually around 1-2 cm in length, and are pollinated by insects.^[12] Each inflorescence contains small white to creamy yellow coloured flowers^[8] with pentamerous campanulate (bell-shaped)^[7] to funnel-shaped petals or corolla that are 2.5-5 mm in length.^[10] Individual flowers have filiform styles and clusters of long white monadelphous stamens.^[7]

The seed pods are straight and cylindrical in form, around 5-10 cm long, with a fetid odor reminiscent of the seed pods of Parkia speciosa and Archidendron jiringa.^[3][8] Pods are packed with edible discoid seeds that are piled above one another. Seeds of this species are creamy yellow when young and darkens to a brown colour as they ripen.^[12] The seed in all stages of maturity are edible and consumed by locals within its range.^[13][14]

This species is native to southern Thailand, Peninsular Malaysia and Sumatra, but has been introduced to Myanmar, the Andaman Islands and Bangladesh.^[1] Trees are usually found growing in lowland primary and secondary forest in sandy loam or lateritic soils. They normally inhabit areas with elevations up to 100 m, but sometimes ascend to elevations of 900 m.^[9] This species is faced with the threat of habitat loss and decreasing population due to deforestation caused by palm oil plantations.^[15]

Trees of this species often emerge in early regeneration forest or regrowth,^[9] becoming a dominant species within them.^[16] The seeds are eaten by frugivores such as orangutans, macaques, squirrels and birds who disperse the seeds across the forest.^[3]

It is a member of the likely polyphyletic Archidendron ser. Clypeariae, which includes species such as Archidendron clypearia, Archidendron jiringa and Archidendron bigeminum whose members are mostly found throughout West Malesia, Mainland Southeast Asia and the Philippines. Its closest relative is Archidendron microcarpum.^[17]

First described by Scottish botanist William Jack in 1822 with Sumatra as the type locality, it was placed in the genus Inga as Inga bubalina.^[7] The type specimen collected is now unknown regarding its whereabouts.^[18]

In 1844, English botanist George Bentham then combined Inga bubalina under Pithecellobium bigeminum var. bubalinum, mistakenly based on a specimen of Archidendron microcarpum collected in Penang.^[18] However, he believed the seed pod from that specimen belonged to a species of Cassia, near Cassia fistula.^[19] This classification was then revised in 1875 when Bentham accepted the pod as belonging to the specimen, while also referring to two other specimens, renamed Pithecellobium bigeminum var. bubalinum as Pithecellobium bubalinum.^[20] Tangentially, in 1876, German botanist Wilhelm Sulpiz Kurz misinterpreted Pithecellobium bubalinum as a member of genus Albizzia. Based on it and an additional two different specimens, one actually being a specimen of Archidendron bigeminum from the Nicobar Islands,^[18] he referred Pithecellobium bubalinum under Albizzia bubalina.^[21]

In a taxonomic revision of the genera Archidendron and Pithecellobium by Danish botanist Ivan Christian Nielsen in 1979, multiple species that were formerly in Pithecellobium were moved to Archidendron. This move included the transfer and renaming of Pithecellobium bubalinum to Archidendron bubalinum.^[18]

Consumption of the pods is believed to detoxify the kidneys, help with urinal incontinence,^[22] constipation, prevent or lower the risk of diabetes.^[8][23] They are also believed to aid in regulating blood sugar, controlling hypertension, and preserving youthfulness^[8], including reducing the risk of cardiovascular diseases^[23] and certain cancers.^[24]

In Malaysia, certain communities of Orang Asli like the Temuan use the roots and seeds as medicine to prevent diabetes. The roots are decocted and the seeds are eaten raw, both unripe and ripe, to prevent urination that is considered to possibly lead to death.^[25] It is also used for this purpose by the Jambi people in Sumatra by dry roasting cooked seeds, finely crushing them, and then mixing the crushed seeds with water. This mixture is drunk two times a day.^[15][26]

The young seeds are traditionally eaten by locals in Malaysia and Indonesia as an appetiser or side dish in the form of a salad known as ulam.^[13] They can also be prepared by boiling or frying the seeds, which are then seasoned with salt and spices.^[27]Mature seeds are usually roasted and ground and used as a condiment in certain Padang and Malay influenced dishes like curries, gulai,^[13] and sambal.^[15][28] Some communities consume sprouted seeds, locally referred to lahang, to reduce the smell. The young leaflets are also eaten as a salad as it has the same aroma profile as the seeds.^[15] The seeds of this species are less preferred in younger generations due to its off-putting smell.^[29]

In West Sumatra, the tree's sturdy wood is valued in traditional architecture for making canoe paddles, houseposts, and other durable wooden tools. The foliage is also used as animal feed for livestock.^[13][27]

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  An unopened seed pod of Archidendron bubalinum.
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  An opened seed pod of Archidendron bubalinum, showing the compact discoid seeds contained inside.
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  Individual seeds of Archidendron bubalinum, peeled and unpeeled.
• 
  Seeds of Archidendron bubalinum being sold in a market in Bengkulu, Sumatra.