Pawpaw Asimina triloba – Native Plant of the Week

Introduction

The Pawpaw or Asimina triloba is a member of the Annonaceae family and the only one that can be found in a temperate climate. The Annonaceae family is part of the Magnoliales Order of flowering Angiosperms. Magnoliales are part of the Magnoliids, the basal angiosperms that diverged before the dicots and monocots. They share characteristics with monocots, dicots, and even gymnosperms, making them an interesting, unique, and varied group of plants. Asimina triloba is no exception to this rule. They produce gorgeously unique flowers and the largest fruit native to the USA (excluding gourds which, for the purposes of edibility, are classified as a vegetable even though they are, in fact, a fruit). The fruit is a delicious creamy fruit with large black seeds you generally do not eat, but the flesh of the fruit tastes somewhat like bananas, and sometimes people call it Indian Banana.

Description of Pawpaw Asimina triloba

Stem & Leaves of Asimina triloba

Pawpaw is a shrub or small tree 1.5 – 11 (-14) m tall with slender trunks to 20(-30) cm in diameter. Its bark is brown on branches and often smooth and light grey on the trunk, but it can get shallow grooves in larger specimens. Branches are slender and spread in an ascending manner. New shoots are moderate to very brown-hairy apically but become glabrous with age.

The leaves of Asimina triloba are simple oblong–obovate to oblanceolate in shape and 15 – 30 cm long. They grow on a petiole 5 – 10 mm long. Leaves are membranous with a narrowly cuneate base and acute to acuminate apex. Leaf margins are margins sometimes partly revolute (rolled under). Leaf surfaces are densely hairy, abaxially becoming sparsely hairy on the veins with age. On the adaxial (upper) side, they are sparsely appressed-pubescent on the veins and become glabrous with age.

Flowers & Fruits of Asimina triloba

The maroon flowers appear in early spring as the leaves are just beginning to grow. Flowers appear in leaf axils on a nodding peduncle 1 – 2.5 cm long that is densely hairy with dark-brown or red-brown hairs. Flowers are 1 – 5 cm in diameter and have an unpleasant odor. Flowers have 3 triangular-deltate sepals 8 – 12 mm long that are densely pilose on the abaxial side. The three outer petals are excurved, oblong–elliptic, and 1.5 – 2.5 cm long. The inner petals are elliptic and usually about 1/3 to 1/2 the length of the outer petals.

The androecium is a ball of short, stocky stamens with upright anthers. The styles of the gynoecium protrude through the center of this mass.

The Pawpaw is somewhat unusual in that it may be polygamomonoecious or polygamodioecious in that it has separate male, female, and hermaphroditic flowers on the same individual or may have male and hermaphrodite on one plant and female and hermaphrodite on another. Furthermore, under stressful conditions, it may change its sex or its ratio of male to female flowers. It is not capable of self-fertilizing.

Its fruit is a large berry 5 – 15 cm long that is green when young and yellow when ripe. Its yellow or orange-colored fruit inside is soft and creamy and contains many large chestnut-brown seeds that are 1.5 – 2.5 cm long. Though its seeds are fertile and it is capable of sexual reproduction, it reproduces more often and more quickly by vegetative spread by way of root suckers.

Similar Species Asimina triloba is Frequently Confused With

Asimina triloba is sometimes mistaken for various Carya, Nyssa, Lindera, Juglans, Quercus, Castanaya, Diospyros, and Magnolia species due to the shape of the leaves. However, the unique flowers and, later the very large fruits will easily distinguish them from any of the species of those genera. There are other species in the Asimina genus that they could be confused with. These can be differentiated as follows:

• Asimina parviflora – this one is restricted to the southeastern US states and does not grow as far west or north as Asimina triloba. It is also much smaller, usually a shrub or a small tree up to 6 m tall. It has similar colored flowers, but they are much smaller, 1 – 1.7 cm in diameter. The fruits are 3 – 7 cm long.
• Asimina incana – a rarer shrub endemic to Florida and Georgia, grows only 1.5 m tall. Its outer petals are white or cream in color instead of maroon, and they are 3.5 – 7 cm long each. Its fruit is a yellow-green berry up to 8 cm long.

Distribution of Pawpaw Asimina triloba

In Canada, Pawpaw is found only in southern Ontario.

In the USA, Pawpaw is an eastern species found in Nebraska, Kansas, Oklahoma, Texas, Iowa, Missouri, Arkansas, Louisiana, Wisconsin, Illinois, Indiana, Ohio, Michigan, Kentucky, Tennessee, Mississippi, Alabama, Georgia, Florida, South Carolina, North Carolina, Virginia, West Virginia, Washington DC, Delaware, Maryland, Pennsylvania, New Jersey, New York, and Connecticut.

Asimina triloba is not found in Mexico.

Habitat & Growing Conditions of Pawpaw

Pawpaw likes to grow in floodplains and shady, rich valley bottoms or lowlands where it may form dense, clonal undergrowth as a patch or thicket of individual small trees. They grow in full sun and part shade. Although shade-tolerant, pawpaws do not grow in undisturbed old-growth forests. Instead, they are one of the newer invaders of clear cuts; generally, around 4 years after tree removal, they will appear.

Pawpaw prefers rich loamy soils with a moderately acidic pH. It prefers moist soil types that are well-drained. While it can tolerate wet, heavy soils, it grows better in those that are well-drained, and it will not grow if the soil is wet for too long.

Growing Pawpaw in Your Garden

Growing species native to your area is a great addition to your garden. Once established, they require little to no maintenance of any kind. They already grow in your area without water or fertilizer, so they will easily grow in your yard if you live in their range. They provide important wildlife and biodiversity values as well.

Pawpaw is relatively easy to grow, but fruit production is a little more complex. To grow it as a flowering shrub, purchase a plant from your local native plant nursery. Avoid trying to grow from seed due to unpredictable seed fertility. From seed, it also takes several years in cool, moist conditions before the plant is ready to produce any flowers or fruits.

Choose a sunny or partly shady spot and ensure you have good soil. If your soil is sandy, too dry, or low in organic matter, dig out a roughly 1 cubic meter area and amend your soil with an abundant amount of loam or even compost. Put some amended soil back in the pit (at least 40 cm worth), and then plant your tree, filling in around it with more amended soil. Pawpaws have delicate taproots, so the soil they are planted in must be freshly loosened.

Top dress with compost to feed it and provide extra moisture during the establishment phase. For dry areas or very poor soil, you can also plant it in a bit of a depression to hold extra moisture when it is available. Water throughout the first growing season, keeping the soil moist but not wet.

If your soil is heavy clay or very wet, you can also dig out a pit but amend it with loam and gravel and then be sure to plant it on a mound rather than in a depression or at ground level to provide it with a bit of extra drainage.

Once established, it will require little to no maintenance.

Fruit Production

If you want to produce fruits from your trees, you will need to plant them in full sun. They are self-incompatible, so you will need more than one tree so that they can cross-fertilize. Avoid taking cuttings from the wild because some wild varieties never produce fruits; they like to spread vegetatively, so fruit production is not necessary for their survival. This is one of the few cases you must buy from a nursery specializing in native plants.

Cross-fertilization naturally is poor in Pawpaw trees. The flowers are mildly malodorous and rely on flies and other insects for pollination, which seldom happens often enough for heavy fruit production. Many growers turn to hand pollination to ensure they get enough fruits.

To hand pollinate is simple; you can literally just use your hand or a soft clean, unused paintbrush. Dust the brush or your finger in a flower on one tree and bring it and do the same with a different flower on another tree. Continue this until you have cross-pollinated all of your flowers. This will significantly increase your fruit production.

Winter Maintenance

Prune when the tree is dormant in fall, winter, or spring, depending on your location. Since this is a temperate Annonaceae, it is already adapted to cold conditions and requires no winter care. However, if you live in the northern limit of its range, it would benefit from winter mulch.

Wildlife Values of Pawpaw

The fruits of the pawpaw are frequently eaten by mammals, including raccoons, gray foxes, opossums, squirrels, and black bears. The foul-smelling twigs and foliage are rarely browsed upon by rabbits and the occasional moose; otherwise, they leave the trees alone unless in fruit. Birds are often seen roosting in the trees and will also occasionally feed on the fruits. The Pawpaw is also a larval host plant of the zebra swallowtail butterfly, which consumes some of the foliage.

Status of Asimina triloba

Pawpaw is considered Globally Secure, G5, and Least Concern on the IUCN Red List.

In the USA, Asimina triloba is considered Locally Secure S5 in Indiana, Kentucky, West Virginia, Virginia, Delaware, Pennsylvania, North Carolina, and Georgia. It is considered Apparently Secure S4 in Nebraska. In New Jersey, Pawpaw is considered Vulnerable S3. It is considered Imperiled S2 in Iowa and New York. In all other states where it is found, it currently has no status rank.

Asimina triloba is considered Vulnerable S3 in southern Ontario. Its range in Canada is very limited and it is found in a heavily populated area of southern Ontario.

Pawpaw is not found in Mexico.

Traditional or Other Uses of Pawpaw

Pawpaw as a Food

The Cherokee, Iroquois, Pawnee, Kansa, and Choctaw people used to eat the fruit fresh or dried. Sometimes they would make it into dried cakes for winter food storage. Dried fruit was sometimes made into sauces or relish.

Today there are commercially grown Pawpaw trees in some areas for small-scale commercial production. They cannot be produced on a large scale for fresh consumption because they quickly ripen and start to ferment upon picking, making them suitable for fresh local markets only. The fruit is also popular in ice cream and baked desserts, where it can be used in frozen form.

Pawpaw as Medicine

There was no recorded use of Native Americans using the Pawpaw as medicine.

However, the bark, leaf, and seed are occasionally used to make modern herbal medicines. They are used in homeopathy to treat fever, vomiting, pain, and inflammation of the mouth and throat.

Asimina triloba as Ornamentals or Tools

The Cherokee people used to use the tough inner bark as a source of cordage to use as strong rope or string for tying things together.

The Pawpaw is often used for landscaping in the eastern USA due to its easy growth, lovely flowers, its fresh fruit, and its relatively low maintenance needs once established. It has few natural pests and requires no pesticides and little to no fertilizer. It is sometimes used in ecological restoration for its ability to grow in wet soils and form dense clonal mats, which can help prevent erosion.

Ethical Wildcrafting of Asimina triloba

Check the status in your state or province before harvesting since it is imperiled or vulnerable in several states and in the province of Ontario. See the above section on Status. Alternatively, grow it in your garden for both its lovely flowers as well as its tasty fruits.

If you are harvesting Asimina triloba from the wild, as always, use the 1 in 20 rule of Ethical Wildcrafting. Pick one in every 20 fruits you see from a large patch. Be sure to leave lots of fruits for all the wildlife that feed on the ripe fruits.

Wildcrafting and Processing

Picked fruits can be placed in a basket or bowl and brought home for processing.

Pawpaw should generally be eaten soon after picking if eating fresh as it quickly ripens and starts to ferment if left too long. Do not eat either the skin or the seeds of the fruit, as both are toxic to humans. Alternatively, you can freeze or dry the fruits.

To freeze, it is best to first peel the skins and remove the seeds, as these are toxic and should not be eaten. The resulting pulp can be frozen in containers or bags.

To dry the fruits, also skin them first and remove the seeds. Then dry the pulp either in the sun on a hot day with mosquito netting around it to keep the flies out or in a food dehydrator on a low heat setting. Dried fruit can be stored in a labeled glass jar.

References and Resources

Asimina triloba fruits pic from Wikipedia By Scott Bauer, USDA – USDA ARS Image Number K7575-8, Public Domain, https://commons.wikimedia.org/w/index.php?curid=10830

Canadensys Plant Search https://data.canadensys.net/vascan/search

Dictionary of Botanical Terms – by Lyrae’s Nature Blog https://lyraenatureblog.com/blog/dictionary-of-botanical-terms/

Eflora Plants of North America http://www.efloras.org/browse.aspx?flora_id=1

iNaturalist Plant Search https://www.inaturalist.org/home

IUCN Red List https://www.iucnredlist.org/

Native American Ethnobotany http://naeb.brit.org/

NatureServe Explorer https://explorer.natureserve.org/Search

USDA Plants Database https://plants.sc.egov.usda.gov/home

Wikipedia on Asmina triloba https://en.wikipedia.org/wiki/Asimina_triloba

Willis, Lyrae (Unpublished).  Plant Families of North America. 

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