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, ylang-ylang and soursop, and it is the only member of that family not confined to the tropics.
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.
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.
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. In many recipes calling for bananas, pawpaw can be used with volumetric equivalency.
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. Pawpaw fruit may be eaten by foxes, possums, squirrels and raccoons. However, pawpaw leaves and twigs are seldom bothered by rabbits or deer.
This colonial tree has a strong tendency to form colonial thickets if left unchecked.
Growers hope that potential medical use will eventually lead to increased market demand from the pharmaceutical industry.
The seeds also have insecticidal properties. The Native Americans dried and powdered them and applied the powder to children's heads to control lice; specialized shampoos now use compounds from pawpaw for the same purpose.