Sapindaceae: The Soapberry Family

What do maples, lychees, and soapnuts have in common?

As the maple leaves turn from green to red and orange this fall, you may be surprised to learn not just a few things about this ubiquitous Wisconsin tree but also its far-off relatives on the other side of the world. Who would have thought that the lychee was a relative of the maple? Or that there are plants that are “soapy”?

The soapberry family (Sapindaceae) is one of the most intriguing families of plants I have yet found. There are nearly 2,000 species ranging from lychee and other tropical fruits (longan, rambutan, ackee), maples, soapberries, guarana, and horse chestnut. The family is closely related to the citrus family (Rutaceae) and in some of the pictures below you may see the resemblance to the green, glossy, thick leaves of citrus.

The hop tree (Arfeuillea arborescens) exhibits features that characterize many species of this family: splitting fruit with contrasting colors, hard black seeds inside red hairy or papery outer casements, and sometimes winged seeds. Credit: Wikipedia Commons.

Tasty Fragrant Fruits

This family has several edible fruits, some that are only just beginning to hit American grocery stores like lychee and rambutan.

A pink rough-textured outer shell covers translucent white floral and sweet fruit inside.
This fruit, like many others in this family, is actually an aril that covers the black seed.

The lychee is a tropical fruit common in Asian markets and growing in popularity elsewhere. Lychee cultivation dates back to the 11th century; during the Han dynasty they were a popular gift item with a special horse courier service to deliver them.

Longan (Dimocarpus longan). Credit: Wikipedia Commons
The name translated in Chinese to dragon eye because the fruit looks like an eyeball. Credit: Wikipedia Commons.

The longan (Dimocarpus longan) is another commercial Asian fruit with a similar taste to lychee. Although it has been cultivated for nearly 2,000 years, it’s relatively new to the rest of the world.

Rambutan (Nephelium lappaceum). Credit: Wikipedia Commons.

Where you find lychee, you often find rambutan. The spiky red shells, which are hairy to help with transpiration, cover a translucent white flesh inside like the lychee.. The fresh fruits have a short shelf life and attempts to cultivate them in the U.S. have failed.

The taste and texture of both rambutans and lychees is reminiscent of grapes but with a more floral flavor.

Other rambutan-like species include the korlan (Nephelium hypoleucum)…
…the hairless rambutan (N. xerospermoides) which is hairless because it has no spines…
…and the pulsan (N. ramboutan-ake), sweeter than rambutan and lychee but rarely found outside of southeast Asia. The name originates from Malay word for twist which suggests the way the fruit is opened. Credit: Wikipedia Commons.

The ackee or akee apple (Blighia sapida) is a delicacy throughout the Caribbean, with ackee and saltfish being Jamaica’s national dish. It has a nutty flavor; almost 50 cultivars are grouped into “butter” or “cheese” types based on color and shelf life. The arils must be properly prepared and cooked; they are parboiled, fried in butter, cooked in stews and curries or with fish and vegetables, and so on. However, the unripe aril and remaining parts of the fruit contain poisons known as “soapberry toxins.” Enough people succumb to eating unripe arils that there is such a thing as Jamaican vomiting sickness, otherwise known as ackee sickness.

Ackee or akee apple (Blighia sapida). The aril is the cream-colored thing surrounding the blue-black seeds. The rest of the fruit is poisonous. Credit: Wikipedia Commons.
Ackee & saltfish, the national dish of Jamaica. Credit: Wikipedia Commons.

Quenepa (Melicoccus bijugatus) fruits look like limes to which this family is a close relative. However, the inside is more like the lychee with peach-colored translucent bittersweet gelatinous flesh. The fruits are eaten fresh or canned and used in beverages.

Guarana and Fish Poison

In addition to fruits, other edible uses of plants in this family include guarana, a coffee-like stimulant, and fish poison to help catch fish.

Guaraná beverage.

Guaraná (P. cupana) is especially common in Brazil. Its concentration of caffeine is twice as high as in coffee. It is used in energy drinks, herbal teas, and as an herbal supplement. Several Brazilian sodas incorporate guarana. The word is Portuguese though it originates from native Guaraní, roughly translated as “fruit like eyes of the people” or “eyes of the gods” because the split fruit looks like an eyeball.

The fruit of pitomba (T. esculenta) native to Amazon Basin is eaten fresh and juiced, the sap used for fish poison.

Another use of many species in this family that indirectly leads to food is as fish poison. For example, the saponin in the bark of guioa or wild quince was used by indigenous Australians as fish poison, and foambark is so called because the saponins in the bark foam after it rains, which indigenous Australians used as soap as well as fish poison.

Ohio buckeye (Aesculus glabra). Credit: Wikipedia Commons.

The California buckeye (Aesculus californica) was used by native Americans to stun fish; the plant could also be eaten after boiling and leaching of the saponin toxins after which the seeds could be ground into flour similar to acorn meal. They did this also with Ohio buckeye (Aesculus glabra, shown above). If not leached out, buckeyes readily supply saponins that produce a lather when the seeds are crushed and mixed with water.

Soaps and Beads

The Indian soapberry or washnut (Sapindus mukorossi) grows in the lower Himalayas. Credit: Wikipedia Commons.

One of the most intriguing aspects of this family is that many of its species contain saponins and are used as soaps for washing, especially the soapberries and soapnuts of the Sapindus genus. Soapnuts are an actual product you can buy as a an eco-friendly (and sensitive skin safe) laundry detergent alternative. Unlike commercial detergents, they do not fade colors.

Soapnut is also used as a natural dye particularly for Tussar silk yarn (which comes from silkworms) and cotton. Tussar silk itself is a popular addition to soap because it gives a silky, slippery feeling to the soap. Credit: Wikipedia Commons.

Some of these “berries” are strung as decorative beads too. The seeds of the Oahu soapberry are strung in leis. The rerak species is also used for its seeds and fruits in the form of buttons and beads. Wingleaf soapberry seeds are made into buttons and necklaces.


The maples genus, Acer, has about 130-160 species, most of them trees native to Asia where they are the most common genera of trees.

Personally, I never would have guessed that maples were a part of this family and part of me is still suspicious. Apparently they are sometimes classified in their own family, Aceraceae. Plant taxonomy is always an evolving field as plant research techniques become more refined.

Samara closeup of Acer acuminatum, native to the Himalayas. Credit: Wikipedia Commons.

They typically have recognizable winged fruits which are called samaras and helicopters. The seeds are enclosed in nutlets attached to each of the papery wings. The samara spins as it falls so that the seed can be carried a distance; each tree can produce hundreds of thousands of seeds.

Boxelder maple (Acer negundo) female flowers. Credit: Wikipedia Commons.
Silverleaf maple female flowers (Acer saccarinum). Most maples are only partially dioecious and have male and female flowers on the same tree, sometimes changing. Credit: Wikipedia Commons.

Leaf color change of the sugar maple. Credit: Wikipedia Commons.

Maples are known for their striking fall colors. Many species are planted for ornamental uses, particularly the Norway maple, silver maple, Japanese maple, and red maple. Aceretums are collections specifically of maples; there is one at the Harvard University arboretum. Maples contribute to “leaf watching traditions” such as sugar maples in fall in North America and in Japan, where the custom of watching maples change color is called omijigari.

Momiji at Ryōan-ji in Kyoto. Credit: Wikipedia Commons.

Maple sap tapping a single tree in my mom’s backyard. This one tree yielded about an eighth of a cup of syrup after many hours of boiling.

Maple syrup is a staple made from the sap of some species during early spring. Sugar tapping and houses can be quite extensive, with multiple taps and tubes connected through the woods to a sugar house where the sap is boiled significantly to concentrate it into the syrup that ends up on shelves. It takes 40 liters of the sap to make 1 liter of the syrup. Though the sugar maple is the most popular tree for this use, followed by the black maple due to their high sugar content, other maples with lower sugar content or more cloudy syrup can be used like sycamore maple, mountain maple, bigleaf maple, redleaf maple, and boxelder maple.

The sugar maple is native to eastern Canada and U.S. hardwood forests where it is a keystone species playing a major role in the forest ecology. It needs cold winters with a hard freeze to enable dormancy; the seeds germinate only when just slightly above freezing which no other tree species is known to do. It is one of the most shade tolerant large deciduous trees meaning it can germinate under a closed canopy and hang out for a while until the canopy opens up. Its roots draw water up from lower in the soil which benefits the tree and surrounding plants. The seeds, after soaking, can be boiled, seasoned, and roasted for a snack; the young leaves and inner back are also edible.

The bigleaf maple (Acer macrophyllum) is so named because it has the largest leaves of any maple. It grows along the northern pacific coast from CA through Canada. Credit: Wikipedia Commons.

Maple wood is also useful: Dried wood is used for food smoking; hardwood species are used for sturdy items like butcher blocks, bowling pins, baseball bats and so on as well as furniture and decorative pieces. It’s also considered a tonewood meaning it carries sound well and is thus used to make musical instruments such as drums, guitar necks, and string instruments.

Maples are very popular ornamentals across Asia. The most known is Japanese maple (Acer palmatum) with many cultivars prized for their ornamental value and their variability in leaf shape, size, fall color, and other aesthetic aspects. Credit: Wikipedia Commons.

Horse Chestnuts

Common horse chestnut (Aesculus hippocastanum) flowers. Credit: Wikipedia Commons.

This family also includes buckeye and horse chestnuts. The trees and their many hybrids are popular ornamentals along streets and parks throughout the temperate world, especially because of their pretty flowers. The seeds are used to play conkers in the UK.

In closing, I leave you with a goofy poem, much like this goofy family of plants.

The Horse Chestnut Fairy 
My conkers, they are shiny things,
And things of mighty joy,
And they are like the wealth of kings
To every little boy;
I see the upturned face of each
Who stands around the tree:
He sees his treasure out of reach,
But does not notice me.
For love of conkers bright and brown,
He pelts the tree all day;
With stones and sticks he knocks them down,
And thinks it jolly play.
But sometimes I, the elf, am hit
Until I’m black and blue;
O laddies, only wait a bit,
I’ll shake them down to you!
Cicely Mary Barker (1895-1973)