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Asimina triloba, the pawpaw, paw paw, paw-paw, or common pawpaw, is a species of Asimina (the pawpaw genus) in the same plant family (the Annonaceae) as the custard-apple, cherimoya, sweetsop, ylang-ylang and soursop. The pawpaw is native to the Eastern, Southern, and Midwestern United States and adjacent southernmost Ontario, Canada, from New York west to southeastern Nebraska, and south to northern Florida and eastern Texas.^[1][2] The pawpaw is a patch-forming (clonal) understory tree found in well-drained, deep, fertile bottom-land and hilly upland habitat, with large, simple leaves and large fruits. The paw paw is the largest edible fruit indigenous to the United States.^[2]

Names

This plant's scientific name is Asimina triloba. The genus name Asimina is adapted from the Native American name assimin^[3] through the French colonial asiminier.^[4] The epithet triloba in the species' scientific name refers to the flowers' three-lobed calices and doubly three-lobed corollas,^[3] the shape not unlike a tricorne hat.

The common name of this species is variously spelled pawpaw, paw paw, paw-paw, and papaw. It probably derives from the Spanish papaya, an American tropical fruit (Carica papaya) sometimes also called "papaw",^[5][6] perhaps because of the superficial similarity of their fruits.^{[citation needed]} Asimina triloba has numerous other often very local common names, at least historically, including: wild banana, prairie banana, Indiana banana, Hoosier banana, West Virginia banana, Kansas banana, Kentucky banana, Michigan banana, Missouri banana, the poor man’s banana, Ozark banana, and banango.

Description

Flowers

Asimina triloba is a large shrub or small tree growing to a height of 35 feet (11 m) (rarely to 45 feet or 14 m) with a trunks 8-12 inches (20–30 cm) or more in diameter. The large leaves of pawpaw trees are clustered symmetrically at the ends of the branches, giving a distinctive imbricated appearance to the tree's foliage.^[3][7]

The leaves of the species are simple, alternate and spirally arranged, entire, deciduous, obovate-lanceolate, 10-12 inches (25–30 cm) long, 4-5 inches (10–13 cm) broad, and wedge-shaped at the base, with an acute apex and an entire margin, with the midrib and primary veins prominent. The petioles are short and stout, with a prominent adaxial groove. Stipules are lacking. The expanding leaves are conduplicate, green, covered with rusty tomentum beneath, and hairy above; when fully grown they are smooth, dark green above, and paler beneath. When bruised, the leaves have a disagreeable odor similar to a green bell pepper. In autumn the leaves are a rusty yellow, which make spotting pawpaw groves possible from a long distance.^[2][3][7]

Pawpaw flowers are perfect, about 1-2 inches (3–5 cm) across, rich red-purple or maroon when mature, with three sepals and six petals. They are borne singly on stout, hairy, axillary peduncles. The flowers are produced in early spring at the same time as or slightly before the new leaves appear, and have a faint fetid or yeasty smell.^[2][3][7][8]

Fruit

The fruit of the pawpaw is a large, yellowish-green to brown berry, 2–6 in (5–16 cm) long and 1–3 in (3–7 cm) broad, weighing from 0.7–18 oz (20–500 g), containing several brown seeds 1/2 to 1 in (15–25 mm) in diameter embedded in the soft, edible fruit pulp. The conspicuous fruits begin developing after the plants flower; they are initially green, maturing by September or October to yellow or brown. When mature, the heavy fruits bend the weak branches down.^[2][3][7]

Other characteristics:

• Calyx: Sepals three, valvate in bud, ovate, acuminate, pale green, downy.^[3][7]
• Corolla: Petals six, in two rows, imbricate in the bud. Inner row acute, erect, nectariferous. Outer row broadly ovate, reflexed at maturity. Petals at first are green, then brown, and finally become dull purple or maroon and conspicuously veiny.^[3][7]
• Stamens: Indefinite, densely packed on the globular receptacle. Filaments short; anthers extrorse, two-celled, opening longitudinally.^[7]
• Pistils: Several, on the summit of the receptacle, projecting from the mass of stamens. Ovary one-celled; stigma sessile; ovules many.^[7]
• Branchlets: light brown, tinged with red, marked by shallow grooves.^[7]
• Winter buds: Small, of two kinds, the leaf buds pointed and closely appressed to the twigs, and the flower buds round, brown, and fuzzy.^[3]
• Bark: Light gray, sometimes blotched with lighter gray spots, sometimes covered with small excrescences, divided by shallow fissures. Inner bark tough, fibrous. The bark with a very disagreeable odor when bruised.^[3][7]
• Wood: Pale, greenish yellow, sapwood lighter; light, soft, coarse-grained and spongy. Sp. gr., 0.3969; weight of cu ft 24.74 lb.^[3][7]

Ecology

Bark

Asimina triloba, the pawpaw, commonly grows in floodplains and shady, rich bottomlands, where it often forms a dense, clonally spreading undergrowth in the forest, often appearing as a patch or thicket of individual small slender trees. Pawpaws are not the first to colonize a disturbed site (arriving roughly four years after a clearcut), but may become dominant and slow the establishment of oaks and hickories. Although shade-tolerant, pawpaws do not persist in undisturbed old growth forest. Pawpaws spread locally primarily by root suckers; sexual reproduction by seed does also occur, but at a fairly low rate.^[9]

Pawpaw flowers are insect-pollinated, but fruit production is sometimes limited if few if any pollinators are attracted to the flower's faint, or sometimes non-existent scent.^{[citation needed]} The flowers produce an odor similar to that of rotting meat to attract blowflies or carrion beetles for cross pollination.^{[citation needed]} Other insects that are attracted to pawpaw flowers include scavenging fruit flies, carrion flies and beetles. Because of irregular fruit production, some^[who?] believe pawpaw plants are self-incompatible, requiring cross-pollination between trees of different clones (patches).

The fruits of the pawpaw are eaten by a variety of mammals, including raccoons, gray foxes, opossums, squirrels, and black bears.^[9]

The disagreeable-smelling leaves, twigs, and bark of pawpaws contain natural insecticides known as acetogenins.^[10] Pawpaw leaves and twigs are seldom consumed by rabbits, deer, or goats,^[11] or by many insects.^[2] However, mules have been seen eating pawpaw leaves in Maryland.^[12]

Larvae of the zebra swallowtail (Eurytides marcellus), a butterfly, feed exclusively on young leaves of Asimina triloba and various other pawpaw (Asimina) species, but never occur in great numbers on the plants.^[11] Chemicals in the pawpaw leaves confer protection from predation throughout the butterfly's life, as trace amounts of acetogenins remain present, making them unpalatable to birds and other predators.^[13]

Biochemistry

Zebra swallowtail butterflies (Eurytides marcellus) with pawpaw foliage

Pawpaw fruits are rich in fatty acids, the major one being octanoate. They also contain cis-δ9- and cis-δ11-hexadecenoate, cis-δ9-, cis-δ11- and cis-δ13-octadecenoate.

The seeds have been shown to contain the chemicals asimitrin (an adjacent ring-hydroxylated bis-tetrahydrofuran acetogenin) and 4-hydroxytrilobin (an adjacent bis-THF ring with two flanking hydroxyl groups and an α,β-unsaturated γ-lactone with a 4-hydroxyl group).^[14] These chemicals seem to have selective cytotoxicity against prostate adenocarcinoma (PC-3) and colon adenocarcinoma (HT-29) cell lines, thus may become a useful chemotherapeutic chemical for these types of cancer.

The leaves also contain toxic annonaceous acetogenins, making them impalatable to most insects. The one notable exception is the zebra swallowtail butterfly (Eurytides marcellus), whose larvae feed on the leaves of various species of Asimina, conferring protection from predation throughout the butterfly's life, as trace amounts of acetogenins remain present, making them unpalatable to birds and other predators.^[13]

The bark of pawpaw trees contains other acetogenins, including asimin, asiminacin and asiminecin, which have been shown to be potent inhibitors of mitochondrial NADH:ubiquinone oxidoreductase,^[15] making A. triloba a promising source of pesticide and anti-tumour compounds.

Conservation status

On a global (range-wide) scale, the common pawpaw (Asimina triloba) has a NatureServe global conservation rank of G5 (Very Common).

In the United States, the species has a NatureServe national conservation rank of N5 (Very Common), but is considered a threatened species in New York, and an endangered species in New Jersey.

In Canada, where the species is found only in portions of southern Ontario, it has a NatureServe national conservation rank of N3 (Vulnerable), and a NatureServe subnational conservation rank of S3 (Vulnerable) in Ontario. The Ontario Ministry of Natural Resources has given the species a general status of "Sensitive", and its populations there are monitored.

In areas in which deer populations are dense, pawpaws appear to be becoming more abundant locally, since the deer avoid them but consume seedlings of most other woody plants.^[12]

History

A strong candidate for the natural distribution of the common pawpaw (Asimina triloba) in North America, prior to the Ice Ages and lasting until roughly 10,000 years ago, was likely the then extant but now extinct megafauna of North America. (Such animals went extinct during the Quaternary extinction event.) With the arrival of humans, and the extinction of such megafauna for distributing Asimina triloba, the likely candidate for distributing these large fruit bearing plants likely became the newly-arrived humans.^[16] The earliest documented mention of pawpaws is in the 1541 report of the Spanish de Soto expedition, who found Native Americans cultivating it east of the Mississippi River.^[17]

Chilled pawpaw fruit was a favorite dessert of George Washington,^[8][17] and Thomas Jefferson planted it at Monticello, his home in Virginia.^[17]

The Lewis and Clark Expedition sometimes subsisted on pawpaws during their travels.^[17]

Uses

Fruits

Asimina triloba is often called wild banana or prairie banana because of its banana-like creamy texture and flavor.

As described by horticulturist Barbara Damrosch, the fruit of the pawpaw "looks a bit like mango, but with pale yellow, custardly, spoonable flesh and black, easy-to-remove seeds."^[18] Wild-collected pawpaw fruits, ripe in late August to mid September, have long been a favorite treat throughout the tree's extensive native range in eastern North America, and on occasion are sold locally at farmers' markets.^[2][18] Pawpaw fruits have a sweet, custardish flavor somewhat similar to banana, mango, and cantaloupe,^[2][3][19] varying significantly by source or cultivar,^[2] with more protein than most fruits.^[2] Nineteenth-century American agronomist E. Lewis Sturtevant described pawpaws as

... a natural custard, too luscious for the relish of most people"^[12]

Ohio botanist William B. Werthner noted that

The fruit ... has a tangy wild-wood flavor peculiarly its own. It is sweet, yet rather cloying to the taste and a wee bit puckery – only a boy can eat more than one at a time.^[3]

Fresh fruits of the pawpaw are commonly eaten raw, either chilled or at room temperature. However, they can be kept only 2–3 days at room temperature, or about a week if refrigerated.^[8] The easily bruised pawpaw fruits do not ship well unless frozen.^[2][18] Where pawpaws grow, the fruit pulp is also often used locally in baked dessert recipes, with pawpaw often substituted with volumetric equivalency in many banana-based recipes. Pawpaws may also be blended into ice cream^[8] or included in pancakes.^[8] Pawpaws are also used for juice-making,^{[citation needed]} as either a fresh pawpaw drink^{[citation needed]} or in drink mixtures (for example, a pawpaw, pineapple, banana, lime, lemon, and orange tea mix^{[citation needed]}). The fruit pulp can also be made into a country wine.^{[citation needed]}

In southern West Virginia, pawpaws are made into a native version of banana nut cake or fruit cake baked inside canning jars, then heat-sealed, reputedly keeping the food for at least a year;^{[citation needed]} however, due to the risk of botulism, preserving cake in a canning jar is not recommended.^[20]

Cultivation

Pawpaws have never been cultivated for their fruits on the scale of apples (Malus domestica) or peaches (Prunus persica), primarily because pawpaw fruits ripen to the point of fermentation soon after they are picked, and only frozen fruit will store or ship well. Other methods of preservation include dehydration, production of jams or jellies, and pressure canning (using the numerical values for bananas).

In recent years, cultivation of pawpaws for fruit production has attracted renewed interest, particularly among organic growers, as a native fruit with few to no pests, successfully grown without pesticides. The commercial cultivation and harvesting of pawpaws is strong in southeastern Ohio,^{[citation needed]} and also being explored in Kentucky^[2] and Maryland,^[12] as well as various areas outside the species' native range, including California,^[11] the Pacific Northwest.,^[11] and Massachusetts^[18]

Desirable kinds (cultivars) of pawpaw are propagated by chip budding or whip grafting. In cultivation, lack of successful pollination is the most common cause of poor fruiting. Cross-pollination of at least two different genetic varieties of the plant is recommended,^[2] and growers often resort to hand pollination or to use of pollinator attractants such as spraying fish emulsion or hanging chicken necks or other meat near the open flowers to attract pollinators. While pawpaws are larval hosts for the zebra swallowtail butterfly, these caterpillars are usually present only at low density, and not detrimental to the foliage of the trees.^[11]

The pawpaw is also gaining in popularity among landscapers and backyard gardeners because of the tree's distinctive growth habit, the appeal of its fresh fruit, and its relatively low maintenance needs once established. However, only container-grown pawpaws should be transplanted; use of bare-rooted pawpaws is not recommended, since their fragile root hairs tend to break off unless a cluster of moist soil is retained on the root mass.^[8]

Insecticide source

The natural insecticides in the leaves, twigs, and bark of pawpaw trees can be used to make an organic pesticide.^[10]

Wood

The wood of tree-sized pawpaws is not commercially valuable.

Habitat restoration

Pawpaws are sometimes included in ecological restoration plantings since this tree grows well in wet soil and has a strong tendency to form well-rooted colonial thickets. The pawpaw is particularly valued for establishing fast-growing vegetation in areas where frequent flooding might produce erosion, since their root systems help hold streambanks steady.^{[citation needed]} Pawpaws grow well even in cold hollows with little exposure to winter sunlight.^{[citation needed]}

Historical uses

The tough, fibrous inner bark of the pawpaw was used by Native Americans and settlers in the Midwest for making ropes, fishing nets, and mats,^[3][12] and for stringing fish.^[4]

Pawpaw logs have been used for split-rail fences in Arkansas.^[3]

The hard, brown, shiny lima-bean-sized seeds were sometimes carried as pocket pieces in Ohio.^[3]

Cultural significance

Old song

A traditional American folk music portrays wild harvesting of pawpaws; Arty Schronce of the Georgia Department of Agriculture gives these lyrics:^[8]

Where, oh where is dear little Nellie?
Where, oh where is dear little Nellie?
Where, oh where is dear little Nellie?
Way down yonder in the pawpaw patch

Pickin' up pawpaws, puttin' 'em in your pocket
Pickin' up pawpaws, puttin' 'em in your pocket
Pickin' up pawpaws, puttin' 'em in your pocket
Way down yonder in the pawpaw patch

He notes that "picking up pawpaws" refers to gathering the ripe, fallen fruit from beneath the trees, and that the "pocket" in the song is that of an apron or similar tie-on pocket, not a modern pants or blue jeans pocket, into which pawpaws would hardly fit.^[8] A "pawpaw patch" refers to the plant's characteristic patch-forming clonal growth habit.

Place names

The pawpaw (Asimina triloba) is the basis for various place and school names in the United States, almost all using the older spelling variant "paw paw".

Lakes

• In Louisiana:
  • Papaw Lake, in Morehouse Parish: U.S. Geological Survey Geographic Names Information System: Papaw Lake
• In Michigan:
  • Little Paw Paw Lake^{[citation needed]}
  • Paw Paw Lake, in Berrien County, the largest and best known Paw Paw Lake
  • Paw Paw Lake, in Hillsdale County: U.S. Geological Survey Geographic Names Information System: Paw Paw Lake
  • Paw Paw Lake, in Kalamazoo County: U.S. Geological Survey Geographic Names Information System: Paw Paw Lake
• In Missouri:
  • Paw-Paw Lake^{[citation needed]}
• In Ohio:
  • Paw Paw Lake^{[citation needed]}
• In Texas:
  • Lake Paw Paw^{[citation needed]}

Streams and river segments

• Paw Paw Creek in Texas in Grayson County, a tributary of Lake Texoma on the Red River^[21]
• Paw Paw Creek, in West Virginia in Marion and Monongalia Counties, a tributary of the Monongahela River
• Paw Paw River, in Michigan in Berrien and Van Buren Counties, near Lake Michigan
• The Paw Paw Bends in the upper Potomac River near Paw Paw, West Virginia, bypassed by the Paw Paw Tunnel on the historic Chesapeake and Ohio Canal.

Towns

• Paw Paw, Illinois, in Lee County
• Paw Paw, Michigan, the county seat of Van Buren County, near Lake Michigan
• Paw Paw, West Virginia, in Morgan County, along the Potomac River across from Maryland

Townships

• Paw Paw Township, Illinois, in DeKalb County
• Paw Paw Township, Indiana, in Wabash County
• Paw Paw Township, Kansas, in Elk County
• Paw Paw Township, Michigan, in Van Buren County

Other places

• Little Paw Paw Lake, Michigan, a populated place in Berien County: U.S. Geological Survey Geographic Names Information System: Little Paw Paw Lake
• Paw Paw, Kentucky, in Pike County near the Virginia border
• Paw Paw Lake, Michigan, a census-designated place in Berien County, the settlement around Paw Paw Lake

Schools

Three U.S. high schools have names based on the pawpaw, due to their location in or near towns named Paw Paw:

• Paw Paw High School (Illinois) – Paw Paw, Illinois
• Paw Paw High School (Michigan) – Paw Paw, Michigan
• Paw Paw High School (West Virginia) – Paw Paw, West Virginia

Art

Yellow-billed Cuckoo (Audubon), with foliage and fruits of Asimina triloba

Nineteenth-century naturalist and painter John James Audubon included pawpaw foliage and fruits in the background of his illustration of the Yellow-billed Cuckoo (Coccyzus americanus) in his classic work, The Birds of America (1827–1838).

Still Life with Pawpaws by Edward Edmondson, Jr., ca. 1870-75

Pawpaw fruits and a pawpaw leaf are featured in the painting Still Life with Pawpaws (ca. 1870-75) by Edward Edmondson, Jr. (1830–1884), at the Dayton Art Institute in Dayton, Ohio.

Other

The Paw Paw Formation, an Early Cretaceous geological formation in Texas.

Pawpawsaurus (Pawpaw lizard), a herbivorous Cretaceous dinosaur from the Paw Paw formation in Texas.

The Paw Paw Tunnel in Maryland on the historic Chesapeake and Ohio Canal, a 3118-foot (950-m) canal tunnel completed in 1850 bypassing the six-mile-long Paw Paw Bends in the Potomac River near the town of Paw Paw, West Virginia, all ultimately named after the pawpaw tree.^[19]

The Paw Paw Railroad (1857–1887), which constructed and operated a 4-mile (6.4 km) rail line between Lawton and Paw Paw, in Van Buren County, Michigan.^[22]

Paw Paws (or Paw Paw Bears), a 1985–1986 television cartoon series.^[23]

The pawpaw (Asimina triloba) was designated as Ohio's state native fruit in 2009.^[24]

Since 1999, The Ohio Pawpaw Growers' Association has sponsored an annual Ohio Pawpaw Festival at Lake Snowden, near Albany, Ohio. The 2011 festival is planned for^{[dated info]} the weekend of September 16–19, 2011.^[25]

References