Why Do Tree Leaves Change Colors in the Fall?

AutumnThe red, gold and purple tones of autumn leaves provide a once-a-year bounty for the eyes. But this phenomenon represents an interesting biological phenomenon, that provides lessons into tree biology, the interconnection between weather and trees and the ecological interactions between trees and their predators.

Unfortunately, the fall color here in the west is not as glorious as that in New England or along the east coast, but there is still plenty of gorgeous foliage to be seen. Aspens turn bright gold, a variety of shrubs and smaller trees produce oranges and other colors, and many of trees of eastern origin produce the prototypical fall fireworks you’d expect elsewhere.

And yes, before anyone asks, you can find pretty awesome fall color in California.

The Basic Process

Trees produce three basic pigments in their leaves:

  • Chlorophyll is a green pigment that is involved in the process of photosynthesis. It is continually created, used and degraded through the growing season, which causes the leaves to appear green.


  • Carotenoids are yellow to orange pigments that are also found inside leaves for much of the year. However, the chlorophyll generally overpowers these pigments, and mask their presence.


  • Anthocyanins are reddish pigments, which are typically not produced in the leaves until the fall.

Whereas chlorophyll and carotenoids are produced in small structures called chloroplasts, anthocyanins flow through the watery material inside the leaf’s cells.

Deciduous trees become dormant in the winter, which alleviates their need to manufacture food (photosynthesis). In fact, because water is often scarce during the winter, dormant trees tend to shed their leaves. This reduces the chances that the water evaporating from the leaves will exceed that which can be drawn from the ground.

So, as the days become shorter and the nights become longer, deciduous trees cease producing chlorophyll. As the chlorophyll breaks down, the underlying carotenoids (which have always been present) and the anthocyanins (which are produced around the same time that chlorophyll production ceases), become visible.

This yields the purple, yellow, red or orange leaves that characterize the season.

A short time later, as the tree prepares for its winter slumber, the leaves form something called an abscission zone at the base of the petiole (leaf stalk). This zone effectively blocks the transport of resources between the tree and the leaf, and eventually serves as an easy point of detachment. Once the abscission zone is complete, the leaf is normally blown off the tree a short while later.

Conditions that Improve Fall Color

You’ve probably noticed that fall color intensity varies from one year to the next, but it also varies from one location to the next – even when all other factors are the same.

But if you look carefully, you’ll notice that the yellow, gold and orange colors tend not to fluctuate from one year to the next; it is the red, maroon and purple colors that are dazzling one year and mediocre the next. Part of that is because the carotenoids which yield the yellows and oranges are present all year long and in similar quantities each year. But anthocyanins are only produced during a relatively small window of time, and the amount produced varies from one year to the next.

It turns out that weather is the primary factor that leads to the differing amounts of anthocyanins. When the days are sunny, the nights are cool and the weather dry, fall color is best. This collection of conditions helps encourage the production and retention of sugars in the leaves, which promotes the production of anthocyanins.

However, a number of other weather conditions can dampen the fall color for a given year. Summer droughts typically reduce the vibrancy of the fall colors, as do warm or wet autumns.

How Do Trees Draw Water from the Ground?

Tree AnatomyMost people understand that trees require water to grow and live, and many are aware that roots play a critical role in drawing water from the ground. But this is the limit of most people’s understanding of the subject.

But by exploring the way in which trees accomplish this surprisingly tricky feat, you can learn a wealth of information about tree biology and you’ll surely appreciate the intricate engineering Mother Nature accomplishes.

Basic Tree Anatomy

Trees pack a whole lot of function into relatively featureless-looking tissues. For example, the wood is actually a complicated type of tissue called xylem. Made from a combination of living and dead tissues, the xylem provides the tree with support and serves as the pipeline for water to travel up the tree.

Xylem contains a number of specialized structures called vessel elements. Comprised almost solely of dead cell walls, the vessel elements form an unbroken tube from the roots, through the trunk and to the leaves. The vessels eventually connect to small pores in the leaf surface, called stomata (singular: stoma).

Another set of plumbing-like tubes are found immediately under the bark of trees in a tissue layer called the phloem. The phloem is tasked with the responsibility of transporting the sugars produced in the leaves to needy tissues throughout the tree. Unlike xylem, which transports water in one direction, phloem is capable of bi-directional flow.

Plumbing and


So far, this all seems pretty intuitive. Trees have long “pipes” which carry water from the roots up through the tree. But the truth is more complicated. Consider, for example, that it usually takes energy to pull the water up from the ground. Just think about how much effort you have to apply to suck a soda through a straw. Trees accomplish similar feats, except that they are often required to draw water for much greater distances.

People often view trees as relatively inanimate objects. They may bloom in the spring and exhibit glorious color in the fall, but people rarely consider the energy required by a tree to grow, produce new tissues and repel invaders. Using energy to draw water up their trunks would increase their energy needs drastically.Fortunately, trees have devised a way around this problem.

The solution relies on a few different physical phenomena or properties.

  • Osmosis begins the process. Simply put, water tends to move from areas with relatively low levels of dissolved substances to areas with relatively high levels of dissolved substances. The fine hairs on the outer surface of absorbing roots contain liquid that has very high levels of solvents. This causes the water surrounding the roots, which are relatively solvent poor, to flow across the root hair’s cell membrane and into the xylem.


  • Now that the water has been drawn into the tree’s xylem, capillary action — the tendency for the water to flow into a narrow tube – becomes important. This occurs when the molecules in the water are more attracted to the vessel walls than they are to each other. This causes some of the fluid to “climb” up the sides of the vessel elements inside the xylem. However, capillary action cannot draw water very high up the tree, so it is only one part of the solution.


Now we have drawn water into the roots via osmosis, and capillary action has helped draw it up to perhaps the level of the trunk (give or take). But to understand the manner in which the water completes its journey, we need to move to the leaves at the canopy’s limit.

Moving On Up

As we said earlier, the vessels inside the tree’s xylem eventually connect to holes in the surface of the leaves called stomata. These pores serve as an exit-point for the water, which evaporates from the pores, diffusing into the air. This process is called transpiration.

But there’s a problem with this – it should be impossible to create this much negative pressure (a fancy way of saying “sucking power”) without causing the water inside the vessels to boil. Trees get around this problem by ensuring that vessel elements are very narrow and 100-percent full of water. Without air bubbles to serve as nucleation sites for the water to start boiling, the water remains in the liquid state. Accordingly, trees are able to use transpiration to achieve high negative pressures, which draws the water from the bottom of the trunk all the way to the leaves at the edge of the canopy.

As you can see, there’s a lot to the process by which trees draw water from the ground. This is a simplified version of the steps, so be sure to check out this great video if you’d like to learn a little more about the process:


Hollies (Ilex spp.)

HolliesHollies are familiar trees, easily recognized by their glossy, dark green foliage and beautiful bright red berries. But hollies are a diverse and varied group, and several species break from this mold. Although the vast majority of holly species are evergreen, a handful shed their leaves annually; some have spiny leaves, while others bear smooth, round foliage; and while bright red berries are iconic, some species bear yellow or black fruit.

Hundreds of species have been described worldwide, but a few – notably the American holly and European holly – are the most commonly used in ornamental plantings.

Wildlife Interactions

While holly fruits (technically, holly fruits are drupes, rather than berries) are toxic to humans and some domestic animals, a variety of wild creatures rely on them for a food source. Insects also feed on the nectar produced by holly flowers, and play an important role in fertilization.

Holly fruits develop from the late summer to the early winter, but most wild animals eschew the drupes until they’ve been through multiple freeze-and-thaw cycles. This appears to soften the previously hard fruits and make them more palatable.

In addition to providing value as a food source, hollies provide very dense cover to rodents and birds foraging amid their boughs. Nesting birds will also set up shop in these dense, often spiny, foliage.

Ornamental Use and Culture

Hollies are quite popular in the ornamental plant trade, and they are available as both wild-type plants and numerous human-created hybrids and cultivars.

Because most hollies are dioecious (plants occur as distinct male and female individuals), it is wise to plant representatives of both sexes to ensure the best possible fruit set. Additionally, while American hollies and a few other forms grow well in the shade, they will produce more fruit when grown in full sun.

Most hollies prefer well-drained, slightly acidic soils, but they are relatively flexible and will adapt to many different growing conditions. Different forms grow best in different places, and most locations have at least one species (typically many more) that will thrive in the area and climate. Taken collectively, hollies thrive in U.S.D.A. Hardiness Zones 3 through 11, which encompasses most of the country.

One down side to their ornamental use is the tendency of some to select non-native species. Most hollies, regardless of their point of origin, produce fruits that are attractive to local birds, who consume the drupes and deposit the seeds elsewhere. This often leads to the spread of invasive holly species, typically at the expense of native hollies and other understory species.

Selected Species Accounts

Species richness estimates for the genus Ilex vary widely. Some authorities recognize only 400 or 500 species, while others recognize nearly 800.

  • American holly(Ilex opaca) – The American holly is an understory species of the southeastern United States, which occasionally grows to about 60 feet in height. When they are grown in open areas with full sun, American hollies often become impressive, pyramid-shaped trees. However, like many other hollies, American hollies are slow-growing trees that take a decade or more to reach maturity. A number of cultivars have been developed, including dwarf forms that make excellent hedges.
  • European holly(Ilex aquifolium)– While European hollies are native to the warmer portions of Europe, their native range also extends into north Africa and southwest Asia.
  • Winterberry (Ilex verticillata)–Winterberry is a large (occasionally reaching 15 feet in height or more), deciduous shrub, native to the Northeastern United States. Celebrated for its glorious red fruit, which are especially conspicuous given the lack of winter foliage, winterberries are a favorite of gardeners. A variety of cultivars are available, with varying tolerance for soil conditions.
  • Mountain holly (Ilex mucronata) –The mountain holly was formerly called the false holly, and placed in the genus Nemopanthus, but recent molecular data has caused taxonomists to place it with the true hollies in the genus Ilex. A North American native, the mountain holly is a shrub that only rarely grows taller than 10 feet. It is sometimes grown as an ornamental shrub or in groups as a hedge.

Cabbage Trees (Cussoniaspp)

CabbageTreesThe genus Cussonia contains about 20 species of trees from southern Africa and the island-nation of Madagascar. The best known and most commonly cultivated species is the common cabbage tree (Cussonia spicata), which hails from scattered locations south of the Saharan Desert. It most often grows in open habitats, such as grasslands or just outside forest margins. Although they don’t grow very quickly in their native lands, they are very fast growers when provided with supplemental water.

Basic Description

Most cabbage trees grow about 30 to 40 feet tall, but occasional specimens may become quite large and approach 60 feet in height. They tend to produce a long, thick trunk and a rounded, spreading canopy. Cabbage tree leaves grow in terminal clusters at the ends of short, soft stems. The limbs and stems often grow in a gnarled, twisted fashion. Cabbage trees have bizarre, divided leaves, that are partially responsible for the tree’s unique aesthetics.

Cabbage trees have thick, corky gray bark which would draw more attention, were it not for the plants unusual, spiky inflorescences. Some even describe them as looking like a candelabra.

Medicinal Usage

Many folk remedies rely on cabbage trees, and Western medical professionals are beginning to investigate the properties of various cabbage tree extracts. Local people use a tea made from the bark of cabbage trees to treat malaria and heartburn, while elixirs produced from the roots of the tree are used to treat venereal disease and as a diuretic. While the common cabbage tree is thought to be the primary species used medicinally, but the mountain cabbage tree is also an important medicinal species in its range.

Food Value

While cabbage trees do not represent a significant source of calories for people sharing their native range (nor are they cultivated specifically as a food source), their roots are edible when mashed and boiled. Cabbage trees also provide sustenance for a variety of wildlife species. A variety of caterpillars feed on the leaves of the plant and spin their cocoons on its leaves, while elephants feed on the foliage and seeds.

Select Species

  • Common cabbage trees (Cussonia spicata) – Common cabbage trees are the most commonly seen and cultivated members of the genus. Common cabbage trees thrive in U.S.D.A. Hardiness Zones 9b to 11. Most cabbage trees are tolerant of mild frosts, although prolonged winter cold snaps may kill them off. Mountain cabbage is thought to be more cold tolerant than the common cabbage tree.
  • Mountain cabbage tree (Cussonia paniculata) – Mountain cabbage trees are another relatively well-known species in the genus Cussonia. The mountain cabbage tree often grows in difficult environments, and it typically grows rather slowly. Even the tallest specimens rarely exceed 20 feet in height. The mountain cabbage tree is a popular ornamental in some areas, and, thanks to its modest size, it is often suitable for container plantings.
  • Cape Coast Cabbage Tree (Cussonia thyrsiflora) – Hailing from the South African Cape region, the Cape coast cabbage tree is a hardy species, that can thrive in sandy, acidic or clay-heavy soils. Growing to about 15 feet in height, this evergreen species makes an interesting addition to gardens in Mediterranean climates.


aralia_elata_en_fleur4081-1Aralia is a genus of nearly 70 different species that exhibit a diverse array of growth habits. Some reach tree-like proportions, while others are nothing more than shrubs. Some of the large varieties grow as multi-stemmed plants, slightly reminiscent of both bamboo and tropical palms. Many members of the genus bear impressive spines, which lead to common names like spikenard, Hercules’ club and Devil’s walking stick.

Distinctive Leaf Arrangement

Despite their varied characteristics, all species in the genus Araliahave very distinctive, bi-pinnately compound leaves. This means that instead of having leaves that connect directly to the twigs via a small stem (simple leaves), or having leaflets which combine to form a single leaf (compound), Aralia plants have stems that emerge from the twig, and split into a collection of sub-stems, each of which bear several leaflets. At a glance, the leaf appears to contain two ranks of twigs.

Growth and Culture

Aralia species grow naturally in several parts of the United States, so they can often be seen in forests and other natural habitats. However, they are also grown ornamentally as specimens, hedges or borders. In fact, some people have begun growing Aralia species indoors. This is possible in part because many Aralia are understory species that grow well in low light levels, and remain small enough to work in interior applications.

Notable Species

Despite the number common traits found across all species in the genus, Aralia species still exhibit considerable diversity. Some of the most noteworthy species include:

  • Devil’s walking stick (Aralia spinosa) – The Devil’s walking stick is native to the southeastern United States, from upstate New York across to eastern Texas. It prefers well-drained soils and does best in U.S.D.A. Hardiness Zones 4 through 9. Devil’s walking stick is an understory species, that thrives best in partial- to full-sun. Some people eat the tender young leaves of this plant, and Native Americans often incorporated the seeds into their diet.
  • American spikenard (Aralia racemose) –Native to the eastern United States, the American spikenard is an ornamental species, prized for its attractive foliage and dark red fruit. Like many other Aralia species, the American spikenard thrives in shady habitats.
  • California spikenard (Aralia californica) –Unlike some of its eastern relatives, which range through a dozen or more states, the California spikenard is only native to California and parts of Oregon. Although it never becomes woody, this attractive shrub may approach 10 feet in height. Known locally as elk clover, California spikenard features long, divided leaves. A popular ornamental plant, the California spikenard thrives in U.S.D.A. Hardiness Zones 3 through 8.
  • Japanese spikenard (Aralia cordata) – Because it grows as an herbaceous perennial, and its new shoots are eaten by many of those who live alongside it, the Japanese spikenard is also known as mountain asparagus.Reaching about 6 feet in height, Japanese spikenard is a fast-growing plant that thrives best in acidic soils. It commonly grows on wooded hillsides in Eastern Asia.
  • Japanese angelica tree (Aralia elata) –Like those of the Japanese spikenard, the young shoots of the Japanese angelica tree are also widely consumed by humans. This species grows in a tree-like form, occasionally reaching 30 feet or more in height. Like the Devil’s walking stick, the Japanese angelica tree produces sharp bark prickles which help to protect the trees from predators.

Yellow Oleander (Thevetia peruvianasyn. Cascabela thevetia)

Yellow OleanderHailing from Mexico and Central America, the yellow oleander (Thevetia peruviana) is a large shrub or small tree adorned with beautiful yellow to peach flowers, that are very popular among gardeners and homeowners.


The classification and composition of the genus Thevetia is cloaked in controversy. Some authorities consider the genus to be a part of the genus Cascabela, while others maintain that, while the two groups are closely related, they remain distinct. In either case, there are between three and eight species recognized, with the yellow oleander (Thevetiaperuviana syn. Cascabelathevetia) being the most commonly encountered form.


All parts of the yellow oleander are poisonous – even the milky sap. Ingestion typically leads to cardiac symptoms and electrolyte imbalances, which may be fatal without medical attention. Humans aren’t the only species susceptible to the poisons, as dogs, cats and horses may also suffer ill effects after eating the plant. Nevertheless, a few birds– including Indian gray hornbills (Ocyceros birostris) and several bulbul species (Pycnonotus spp.) — feed upon the plant’s fruit without apparent problem.

The plant’s toxins were so widely respected among Central Americans that the tree was often called the cascabel (a Spanish word often applied to rattlesnakes), which is a reference to its ability to kill as readily as a rattlesnake can.

Growth and Culture

Yellow oleanders are heat-loving trees who prefer warm temperatures and ample sunlight. Plant them in exposed, sunny locations whenever possible, but they will usually survive in areas of partial shade.They are best suited for U.S.D.A. Hardiness Zones 9 and 10, although they are also grown in Zone 8, although precautions must be taken to protect the plants from unusually cold temperatures.

Despite their tropical native range, yellow oleanders grow well in Mediterranean climates – such as those found along much of California’s coastline. While their growing location must be well-drained, they typically adapt well to most soils. While they are generally considered a reasonably drought-tolerant species, your plants will appreciate supplemental water during dry spells.

In general, yellow oleanders are low-maintenance plants, that cause their caretakers little trouble. They are often pruned while small to encourage them to develop a tree-like growth habit, but thereafter, the pruning needs of these small trees are relatively minor. The tallest specimens may reach 20 feet, but most will remain under 10 feet tall. They do produce hard, black to red seed capsules, which present an annual litter problem, but they are otherwise unimposing.

Invasive Species

Thanks to its popularity, yellow oleander is cultivated and grown in suitable climates around the world, including India, Sri Lanka and other portions of South Asia. In many of these places, the plants have escaped cultivation and spread throughout natural habitats, where it has become an invasive species. Although the plant has some wildlife value, it also outcompetes a number of native species, to the detriment of the habitat and greater ecosystem.

Some of the locations in which yellow oleander has become naturalized include Australia, Tanzania, Uganda and portions of East Africa. It has also established itself on many Pacific Islands and some parts of the U.S. One important side effect of this species’ range expansion is the danger it represents to domestic or agricultural animals who may feed upon the plant’s flowers or seeds.


OleanderNamed after their superficial resemblance to olive trees, Oleander (Nerium oleander) is an attractive shrub or small tree that thrives in a Mediterranean climate. Originally hailing from North Africa and West Asia, property owners can now purchase oleanders in any of more than 400 different forms.

Size and Shape

Oleanders most commonly grow as large, bushy shrubs, but some specimens develop a tree-like size and shape. Most oleanders are only a few feet tall, but the largest examples may reach 20 feet in height. When large, oleanders tend to exhibit an umbrella-like growth habit. Their stems grow in a relatively narrow clump, but the tops of the branches spread out and cascade toward the ground.

Flowers and Foliage

Oleander leaves are dark green and arranged in pairs (although they occasionally feature a whorled leaf arrangement). An evergreen plant, oleander remains quite attractive throughout the year.

Nevertheless, people do not typically fall in love with oleanders because of their dark green leaves – the flowers are the oleanders’ claim to fame. Sweet-scented and abundant, oleander flowers are as beautiful as they are plentiful; they often bloom throughout the entirety of the warm season. Most oleanders have white or pink flowers, but some cultivars yield flowers ranging from yellow to red.

Unlike many other flowers that depend on the help of insects for pollination, oleanders do not appear to provide any benefit to the insects that visit them. Instead, they appear to use deceptive practices to trick bees into visiting the flowers, even though they produce no nectar on which the bees can feed.

The downy seeds are released from long, thin pods; they take to the air and drift far away when strong winds blow.

Terrible Toxins

While they do not appear to be toxic to many rodents or birds, oleanders are toxic to humans and some other animals. The toxins produced by the plant may cause gastrointestinal upset, heart rhythm problems and even nervous system disturbances – in some cases consumption has resulted in death. However, many tales of oleander poisoning are little more than myths. While you should certainly avoid consuming any part of the plant (all tissues potentially bear the toxic components), human deaths from consuming the plant are relatively rare.

Some people report that contact with the sap of oleanders can cause a skin rash, so caution is advised when contacting the plants. Many insects that feed upon the leaves sequester the ingested toxins and use them as a defense mechanism. Because they are toxic, oleander trees and shrubs typically receive little damage from deer and rabbits.

Geography for Growing

Oleanders grow best in USDA Hardiness zones 8 through 10, but many people have successfully grown them outside of this range. Tough plants, oleanders can handle a wide array of challenges, including high temperatures, periodic drought, periodic flooding, compacted soils, salt spray and high pH levels. However, they are very sensitive to temperatures below about 20 degrees Fahrenheit. When exposed to such chilly temperatures, they almost always suffer damage.

However, if protected from low temperatures, oleanders can thrive just about anywhere. Many people grow them as indoor, potted plants and move them outside during the summer. Alternatively, they can be grown inside the climate-controlled confines of a greenhouse.

Custard Apples

Custard Apples

Custard Apples

The term custard apple tree is applied in two different ways: Some use it to describe all members of the genus Annona, while others only apply the name to the species Annona reticulata. Fortunately, while the genus Annona is quite large (with approximately 150 to 175 species, depending on the authority consulted), the species all share a variety of similar traits.

Most custard apple tree species are native to Central America and Africa, although several species have been domesticated and are grown in suitable climates the world over. The fruit of several species has significant commercial value, particularly in the developing world.

Size and Shape

Custard apples are medium-sized trees that usually reach heights of between 15 and 40 feet. They aren’t considered especially attractive trees, so they are typically grown for food production rather than as ornamentals. Additionally, custard apple trees have very soft wood that breaks easily – particularly when the branches are weighed down with a full fruit crop. Most commercial custard apple farms utilize wind breaks to help protect their trees and maximize their crop.

Nevertheless, custard apple trees can be planted ornamentally, although they only thrive in U.S. Hardiness Zones 7 through 9. Skillful pruning can improve their appearance and help keep them looking their best. Despite the fact that they aren’t ideal shade trees, they do offer most of the same benefits that similarly sized trees do (such as providing shade and wildlife habitat as well as reducing local temperatures).

Their deciduous leaves are about 5 to 8 inches long and rather narrow. They are typically dark green on their top surface and lighter green beneath.

Fruits and Flowers

The flowers of custard apple trees are somewhat bizarre-looking. In fact, they never open completely the way most other flowers do. They bear three extraordinarily long outer petals and three smaller inner petals (the inner petals are very difficult to see). This flower construction belies their close relationship with paw paws (Asimina spp.). Large horned beetles appear to be the primary pollinators of most Annona species.

The resulting fruit is somewhat large and equally strange. Varying in shape from oblong to spherical (and occasionally heart-shaped), the ripe fruit varies between yellow and red in color. The taste is described as being custard-like, which is the reason for their common name.

Growing Tips

Custard apples grow best in very well drained soils. Although they do produce a significant taproot extending vertically below the trunk, the bulk of the absorbing roots reside in the upper layers of the soil. However, these trees are very susceptible to root rots and bacterial wilt. In fact, The Queensland Department of Agriculture and Fisheries recommends that growers refrain from planting custard apple trees in soils that formerly harbored tomatoes, potatoes, eggplant and several other common crops, due to the likelihood that bacterial spores may already lurk in the soil. However, root-zone issues aside, custard apples do not often succumb to many pests and diseases that afflict other fruiting trees.

Custard apple trees require warm temperatures to thrive, and they grow best in areas with long, humid summers and mild, dry winters. Established custard apple trees can survive moderate droughts, but without ample rainfall and relative humidity levels of 70 percent or more, custard apple trees may shed their leaves and produce a minimal crop.

Toxic Properties

Several components within custard apple trees are potentially bioactive, and several primitive cultures use different parts of the plants for medicinal purposes. Some of the plants in this genus produce toxic seeds, which can cause a degenerative neurological condition in humans. Strangely, this only seems to occur on the island of Guadeloupe.

The leaves of custard apple trees also bear several bioactive compounds. They not only possess insecticidal chemicals; their tannins are used to make dyes.


Pawpaw Tree

A couple of different species in the genus Asimina go by the name pawpaw, but the common pawpaw (Asimina triloba) is far and away the most commonly encountered species.

Whereas the common pawpaw is found throughout much of the eastern United States, all other members of the genus are restricted to Florida, Alabama and Georgia. Authorities differ on the number of species in the group, with some only recognizing two and others recognizing as many as 10.

While pawpaw trees are somewA Favorite Fruithat interesting looking (especially when contrasted with most other native trees), they offer little value in an ornamental context. Their primary claim to fame is their highly unusual fruit.

A Favorite Fruit

Pawpaw fruit defy easy description. Reaching up to 6 inches in length, they are the largest edible fruit that native to the United States.  Although they start out green, they often bear browns, yellows or even purple tones upon ripening. Technically a type of berry, pawpaw fruits contain a number of hard, inedible seeds.

Most people describe their taste as being similar to that of a banana (they are, in fact, used frequently in place of bananas in desert recipes), while others liken their flavor to that of a mango. Some note hints of papaya or strawberry. Their texture is better characterized as extremely soft and custard-like.   

Those who enjoy the taste often prize them greatly, as they are not easy to acquire via commercial means. Pawpaw fruits are not easy to store for extended periods of time and shipping them is equally problematic – they turn to mush in short order. Some small-scale farmers have begun growing them for local markets, but short of the development of a storable cultivar, they are unlikely to become commonplace in your local grocery store.

However, pawpaws are sometimes available in frozen or preserved form. Some manufacturers have even started creating pawpaw ice cream.

A Taste of the Tropics

Pawpaws look somewhat out of place in eastern forests. Instead of the small, thin, finely toothed leaves of maples (Acer spp.), elms (Ulmus spp.) and birches (Betula spp.), these bottomland-inhabiting trees have large, smooth-edged leaves that look like they belong in a tropical rainforest. Although they can grow to proper “tree-sized” proportions, most wild specimens are rarely more than scraggly denizens of the understory.

While their physical characteristics are partially a manifestation of their habitat adaptations (for example, their large leaves are an adaptation that enables them to collect as much light as possible in the dim forest understory), they are also a manifestation of their evolutionary relationships. Pawpaws are members of the family Annonaceae, which primarily contains trees with tropical distributions. Some of its closest relatives living in the same forests include the magnolias (Magnolia spp.) and tuliptrees (Liriodendron tulipifera).

Funny-Looking Flowers

Pawpaw flowers are very interesting-looking. They bear six petals arranged in two rows – one outside row and an offset inside row. Somewhere between maroon and brown in color, the medium-sized flowers may occur singly or in groups. They’d be relatively inconspicuous were it not for their size.

They are also relatively scent-free, which is good; what smell they do emit is not terribly pleasant. In fact, the primary insects that pollinate the flowers (several beetle species) are those attracted to the smell of decay. Because these are not very effective pollinators, pawpaws produce relatively few fruit relative to the number of flowers they bear.  

Subpar Seed Dispersal

Fruit-set is not the only thing with which pawpaw trees struggle: They are also poor seed dispersers. While plenty of animals also find pawpaw fruits to be delicious — raccoons, coyotes, foxes and opossums eagerly consume the fruit – few of them ingest, and ultimately disperse, the seeds.

To help cope with this evolutionary challenge, pawpaws often reproduce by forming large spreading colonies in hospitable locations. Some scientists have suggested that the poor dispersal pattern of pawpaws is the result of the extinction of a former predator (most likely a big herbivore that could ingest the fruit whole). Once these creatures died off, humans became the primary means by which pawpaw seeds have traveled ever since.