Pawpaw


 * This page refers to the U.S. pawpaw in the genus Asimina. In some other parts of the world, the name pawpaw is applied to the unrelated tropical fruit papaya (Carica papaya).

Overview
Pawpaw (Asimina) is a genus of eight or nine species of small trees with large leaves and fruit, native to eastern North America. The genus includes the largest edible fruit indigenous to the continent. They are understory trees found in deep fertile bottomland and hilly upland habitat. Pawpaw is in the same family (Annonaceae) as the custard-apple, cherimoya, sweetsop, and soursop, and it is the only member of that family not confined to the tropics.

Names
The name, also spelled paw paw, paw-paw, and papaw, probably derives from the Spanish papaya, perhaps due to the superficial similarity of their fruit. Pawpaw has numerous other common names, often very local, such as prairie banana, Indiana banana, Kentucky banana, Michigan banana, and Ozark banana.

Description
The pawpaws are shrubs or small trees, reaching heights of 2 to 12 m tall. The northern, cold-tolerant common pawpaw (Asimina triloba) is deciduous, while the southern species are often evergreen.

The leaves are alternate, simple ovate, entire, 20 to 35 cm long and 10 to 15 cm broad.

The fetid flowers are produced singly or in clusters of up to eight together; they are large, 4 to 6 cm across, perfect, with six sepals and petals (three large outer petals, three smaller inner petals). The petal color varies from white to purple or red-brown.

The fruit is a large edible berry, 5 to 16 cm long and 3 to 7 cm broad, weighing from 20 to 500 g, with numerous seeds; it is green when unripe, maturing to yellow or brown. It has a flavor somewhat similar to both banana and mango, varying significantly by cultivar, and has more protein than most fruits.


 * Bark: Dark brown, blotched with gray spots, sometimes covered with small excrescences, divided by shallow fissures. Inner bark tough, fibrous.  Branchlets light brown, tinged with red, marked by shallow grooves.
 * Wood: Pale, greenish yellow, sapwood lighter; light, soft, coarse-grained and spongy. Sp. gr., 0.3969; weight of cu. ft. 24.74 lbs.
 * Winter buds: Small, brown, acuminate, hairy.
 * Leaves: Alternate, simple, feather-veined, obovate-lanceolate, ten to twelve inches long, four to five broad, wedge-shaped at base, entire, acute at apex; midrib and primary veins prominent. They come out of the bud conduplicate, green, covered with rusty tomentum beneath, hairy above; when full grown are smooth, dark green above, paler beneath.  In autumn they are a rusty yellow.  Petioles short and stout with a prominent adaxial groove.  Stipules wanting.
 * Flowers: April, with the leaves. Perfect, solitary, axillary, rich red purple, two inches across, borne on stout, hairy peduncles.  Ill smelling.
 * Calyx: Sepals three, valvate in bud, ovate, acuminate, pale green, downy.
 * 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 and conspicuously veiny.
 * Stamens: Indefinite, densely packed on the globular receptacle. Filaments short; anthers extrorse, two-celled, opening longitudinally.
 * Pistils: Several, on the summit of the receptacle, projecting from the mass of stamens. Ovary one-celled; stigma sessile; ovules many.
 * Fruit: September, October. Cotyledons broad, five-lobed.

Cultivation
Pollinated by scavenging carrion flies and beetles, the flowers emit a weak scent which attracts few pollinators, thus limiting fruit production.

Larger growers sometimes locate rotting meat near the trees at bloom time to increase the number of blowflies. Asimina triloba is the only larval host of the Zebra Swallowtail Butterfly.

Species

 * Asimina angustifolia Raf. - Slimleaf Pawpaw. Florida, Georgia, and Alabama.
 * Asimina incana (W. Bartram) Exell - Woolly Pawpaw. Florida and Georgia.
 * Asimina obovata (Willd.) Nash - Bigflower Pawpaw. Florida.
 * Asimina parviflora (Michx.) Dunal - Smallflower Pawpaw. Southern states from Texas to Virginia.
 * Asimina pygmea (W. Bartram) Dunal - Dwarf Pawpaw. Florida and Georgia.
 * Asimina reticulata Shuttlw. ex Chapman - Netted Pawpaw. Florida and Georgia.
 * Asimina tetramera Small - Fourpetal Pawpaw. Florida.
 * Asimina triloba (L.) Dunal - Common Pawpaw. Extreme southern Ontario, Canada, and the eastern United States from New York west to southeast Nebraska, and south to northern Florida and eastern Texas.

Cultivation and uses
The pawpaw's chosen home is in the shade of the rich bottom lands of the Mississippi valley, where it often forms a dense undergrowth in the forest. Where it dominates a tract it appears as a thicket of small slender trees, whose great leaves are borne so close together at the ends of the branches, and which cover each other so symmetrically, that the effect is to give a peculiar imbricated appearance to the tree.

Although it is a delicious and nutritious fruit, it has never been cultivated on the scale of apples and peaches, primarily because it does not store or ship well. It is also difficult to transplant due to its long taproot. Cultivars are propagated by chip budding or whip grafting.

In recent years the pawpaw has attracted renewed interest, particularly among organic growers, as a native fruit which has few pests, and which therefore requires little pesticide use for cultivation. The shipping and storage problem has largely been addressed by pulping the fruit and freezing the pulp. Among backyard gardeners it also is gaining in popularity because of the appeal of fresh fruit and because it is relatively low maintenance once planted. The pulp is used primarily in baked dessert recipes, as well as for brewing pawpaw beer.

The commercial growing and harvesting of pawpaws is strongest in southeast Ohio. The Ohio Pawpaw Growers' Association annually sponsors the Ohio Pawpaw Festival at Lake Snowden near Albany, Ohio.

The flowers are self-incompatible, requiring cross pollination; at least two different varieties of the plant are needed as pollenizers. The flowers produce an odor similar to that of rotting meat to attract blowflies or carrion beetles for cross pollination. Lack of pollination is the most common cause of poor fruiting, and growers resort to hand pollination or to hanging chicken necks or other meat to attract pollinators.

The leaves, twigs, and bark of the tree also contain natural insecticides known as acetogenins, which can be used to make an organic pesticide. Acetogenins from pawpaw have also been investigated for their potent anticancer effects stemming from their ability to inhibit NADH oxidase.

This colonial tree has a strong tendency to form colonial thickets if left unchecked.

History
The earliest documentation of pawpaws is in the 1541 report of the de Soto expedition, who found Native Americans cultivating it east of the Mississippi River. The Lewis and Clark Expedition depended and sometimes subsisted on pawpaws during their travels. Chilled pawpaw fruit was a favorite dessert of George Washington, and Thomas Jefferson was certainly familiar with it as he planted it at Monticello. In 2006, following lobbying by the Ohio Pawpaw Growers' Association, the Ohio House of Representatives passed a law that would have declared the pawpaw to be the state native fruit of Ohio. However, the Ohio Senate failed to act on the bill, resulting in its death.

Medicinal properties
Compounds found in the bark and leaves of the pawpaw tree have been investigated and tested for anti-cancer properties because of the chemicals' effect on cell metabolism, particularly by Dr Jerry McLaughlin and his team at Purdue University. Growers hope that potential medical use will eventually lead to increased market demand from the pharmaceutical industry.

In homeopathy, Asimina triloba is used as remedy for scarlet fever and red skin rashes.

The seeds also have insecticidal properties. The Native Americans dried and powdered them and applied the powder to childrens' heads to control lice; specialized shampoos now use compounds from pawpaw for the same purpose.

Recent research has shown that the consumption of Annonaceous fruit may lead to the onset of atypical Parkinson's Disease in human, and a subsequent study has suggested a possible involvement of phytochemicals in the onset of symptoms in rats. Further research is currently underway to investigate the relationship between Annonaceous compounds and neurodegeneration.