Pawpaw

 

Common Name: Pawpaw, Custard apple, Poor-Man’s banana, West Virginia (and several other states) banana – The etymology of Pawpaw is indeterminate though it is postulated that the name is a linguistic variant of Papaya, a tree native to the tropical regions of the Americas; both trees have lobed leaves and oblong fruits. The name Papaya derives from either the Otomac papai or the Carib ababai. Pawpaw is also written as Paw-paw or Papaw.

Scientific Name: Asimina triloba – The genus name is of French-Native American origin and probably derives from rassimina, the name given the Pawpaw by the indigenous Illiniwek (also known as Illini) of the eponymous Illinois region. Here rassi meant equally divided longitudinally (bilateral symmetry) and mina meant with seeds – both referring to the fruit. The species name is to describe the three (tri) lobes (loba) of the flower.

Potpourri: The Pawpaw is a North American original, the quintessential native plant. It is diminutive; an understory tree that occupies the netherworld under the forest canopy, its characteristic large, ovate leaves extended to gather the reduced light that there prevails. What it lacks in stature, it compensates in the singular quality of its namesake fruits; the custard apple is a woodland’s bounty of unexpected taste and texture. Pawpaws have the largest edible fruits of any native North American plant, an observation not lost on the indigenous peoples whose subsistence culture was predominantly hunting and gathering. The pawpaw is accordingly entwined with the historical cultures of the sylvan lowlands of the Native Americans and their colonial successors, a fact confirmed by the surviving reports of the earliest European encroachments into the continent’s interior. [1]

Pawpaw’s have the largest fruits of any indigenous North American plant. They were widely used by Native Americans as edible and nutritious foodstuffs as evidenced by observations of the earliest western encroachments into the continent’s interior. Hernando De Soto, the noted peripatetic Spanish conquistador who traversed a large swath of North America before succumbing to tropical fevers on the banks of the Mississippi River in 1541, reported the widespread cultivation of the trees by the native inhabitants. A narrative published in Portuguese in 1557 by a member of the De Soto party says of the Pawpaw that “It is a fruit … having a very good smell and an excellent taste. It is planted by the natives through all the country.” [2] Several centuries later, the Lewis and Clark expedition reported similar practices. As recorded by Captain William Clark on September 15, 1806: “Passed the entrance of the Kansas River which was very low … We landed one time only to let the men gather Papawa (sic) or the Custard apple of which this Country abounds, and the men are very fond of.” [3] Further interactions with Native Americans revealed that the fruits were gathered and made into dried cakes by the Algonquian, Siouan, Osage and Iroquois tribal groups and that the Cherokee used the bark to make rope for stringing the fish they had caught – a practice retained by the latter-day inhabitants of the Ohio River Valley. [4]

The Pawpaw became a staple of the Appalachian Mountain people, as evident in the children’s Pawpaw Patch Song:

Where, oh where is pretty little Susie? Where, oh where is pretty little Susie? Where, oh where is pretty little Susie? Way down yonder in the paw-paw patch.

Come on, boys, let’s go find her, Come on, boys, let’s go find her, Come on, boys, let’s go find her, Way down yonder in the paw-paw patch.

Pickin’ up paw-paws, puttin’ ‘em in her pockets, Pickin’ up paw-paws, puttin’ ‘em in her pockets, Pickin’ up paw-paws, puttin’ ‘em in her pockets, Way down yonder in the paw-paw patch. [5]

It is hypothesized that the Native Americans not only ate but also actively propagated the Pawpaw trees to the extent that they became pervasive throughout the eastern half on North America as was asserted by De Soto’s narrator. While the pawpaw tree is very good at vegetatively extending shoots from the expansion of extant rhizomes (the ubiquity of the “Pawpaw Patch” in the song reflects their tendency to form patches due to vegetative growth), it is not at all very good at establishing new colonies with the traditional seed dispersal and germination method. The problem is one of poor pollination. Although the Pawpaw forms a perfect flower in having both male and female reproductive organs, it is not self – pollinating. The reason for this anomaly is that it is protogynous, which means that the female stigma matures before the male pollen is shed. A second factor is that Pawpaw flowers have almost no scent, so that they are not very attractive to pollinators. It has been determined experimentally that the overall result of the pawpaw’s lack of fecundity is that only 0.41 percent of pawpaw flowers on naturally pollinated plants result in a fertilized fruit with seeds. Recent efforts to establish commercial pawpaw production have resulted in a 17 percent fertility rate; this was achieved only by pollinating the flowers by hand. [6]

The poor reproductive capability of the pawpaw has inspired scientific speculation concerning the extent of its geographic range that seeks to resolve the conundrum as to how it could have spread throughout eastern North America on its own. The theory that it was a cultivar of Native Americans is weakly plausible; however, a more intriguing hypothesis is that the pawpaw was spread by the now extinct large mammals of the Americas. It is well established in the fossil record that there were once over 40 species of now extinct megafauna, a neologism for any terrestrial animal weighing more than 100 pounds, which roamed the fields and forests of the Americas. Their presence is postulated as an evolutionary reaction to survival during the recurrent ice ages that characterized the Pleistocene Epoch that preceded the current Holocene Epoch from 1.8 million to 10,000 years ago, a wink-of-an-eye in the billion-year geological time scale. Why? Large bodies store more heat in a voluminous bulk relative to its loss over a relatively sparse surface area (volume is a cube of length; surface area is squared). They were a Noah’s Arc of diversity ranging from one-ton armadillo-like glyptodonts to elephantine mastodons and mammoths weighing up to nine tons. [7] However, Noah would have had to add a few dozen cubits to the scantlings of his arc for buoyancy to compensate for their massive girth; they evidently never made the metaphorical ride to Armenia’s Mount Ararat.

Among the curious anomalies of the “poor man’s banana” as the pawpaw is sometimes known are the many large seeds embedded in the edible and succulent pulp. These must have evolved to perpetrate the species through faunal consumption, the essential function of fruit. While possibly a trice tautological but to emphasize the point: The basic premise is that the large seeds evolved in order to pass through the digestive tract of a large animal where they would become activated by the chemistry of the gastro-intestinal tract and deposited in nutrient-rich fecal matter for germination. There is a problem though; no extant large herbivores eat pawpaw. In 1982, it was posited that the existence of various plants having fruits with large seeds was a vestige of the ecology of the prelapsarian Americas before the disruption of human intervention. A large elephant-like quadruped called a Gomphothere has been suggested as the missing link in pawpaw evolution. The empirical underpinnings of the fruit-eating megafaunal theory consist of three elements: (1) That large African mammals that still exist eat fruits similar in taste and texture to the pawpaw; (2) That the current fruits attract a paucity of dispersers; and (3) That many of the current fruits are not consumed by the large herbivores that now predominate (e.g. deer and bears). In addition to the pawpaw, the Osage orange and the honey locust also have an anachronistic aura of being in the wrong place at the wrong time. [8]

What happened to the megafauna of the Americas is a mystery; their extinction is a matter of considerable debate among archaeologists. Humans crossed from Asia on the Beringia land-bridge that emerged across the eponymous Bering Strait near the end of the last ice age some 12,000 years ago. Their diaspora throughout the Americas coincided in time with the megafaunal disappearance; it seems too much of a correlation to question direct causation and that has long been the assertion. However, correlation is not adequate to establish causation. Due to extensive archaeological findings and a better understanding of climate change impacts, there is now considerable doubt as to the veracity of the operative syllogism ‘if they came then they killed.’ The climactic end of the Pleistocene was just that; ecosystems changed to adapt to the warmer weather that resulted. For the megafauna, it was certainly a time of gradual yet inexorable changes to the food supply that their bulk demanded; as the herbivores waned in size and numbers, the predatory carnivores struggled. From the ecological standpoint, it was a time of nature’s evolutionary engine seeking a new normal.

One hypothesis is that the Clovis people, named for their characteristic arrow point projectiles first discovered near Clovis, New Mexico in 1933, had mastered the art of hunting large animals and pursued their hapless quarry across the Americas and extirpated them in the relatively short time span of about 1,000 years. There are a few problems with this hypothesis, known in anthropology circles as the ‘overkill theory.’ There have been 76 sites found to date with animal bones and Clovis points collocated; of these, fourteen have clear signs of slaughter and consumption in the form of blade marks and marrow extraction. All remnant bones are either mastodons or the closely related mammoths; the rest of the megafauna are missing. A second and more compelling observation arguing against invasive human predation is the fate of the most iconic of American megafauna; bison were hunted extensively and exclusively by many Native American tribes for centuries while their numbers expanded exponentially. A herd seen in Kansas in 1871 was estimated to contain 4 million individuals. The bison thrived because they evolved to consume the seas of coarse prairie grass that the warmer climate had favored; evidently the other megafauna did not. At a meeting of several hundred archaeologists in the early 1980’s only one person persisted in the overkill theory; all of the others felt that climate played a major and perhaps singular role [9]

While the impact of humanity’s circumnavigation and relentless expansion into Edenic habitats may be moot where North America is concerned, it has been catastrophic in the case of islands large and small and deleterious at best everywhere else. The depredation of the dodo by Dutch sailors on the Indian Ocean island Mauritius is probably the most well-known example. The flightless dodo that evolved in isolation devoid of predation was defenseless in body and soul; they had no fear of the intruders and no way to fight them. First sighted in the early 16th century, they had all been killed and eaten by the 18th. [10] Interestingly, the pawpaw seed argument was proffered concerning the tambalacoque or dodo tree of Mauritius; when the Dodo’s were decimated by human predation, the trees stopped reproducing. However, scientific skepticism prevailed as it mostly does, and subsequent analyses identified alternative animal vectors for tambalacoque trees, which should probably no longer be called dodo trees to dispel confusion [11]. Before the aboriginal peoples rafted to Australia from the Indonesian archipelago about sixty thousand years ago, the island continent teemed with megafauna including giant flightless birds, twenty-three-foot-long lizards, giant sloths and a car-sized tortoise. They had all disappeared from the fossil record within a few thousand years. The moas of New Zealand were similarly wiped out by the Maori. The Europeans who first debarked in Australia a few hundred years ago have since exterminated 13 of the islands 263 species of mammal. The planetary killers have been on the march ever since, ushering in what many consider a global extinction event of Permian proportions [12]. They are still searching on the island of Tasmania for the last thylacine, a marsupial carnivore that looks remotely like a tiger with a thick, kangaroo-like tail. The last on seen alive died of exposure at the Hobart zoo in 1936. [13]

The popularity of the pawpaw among Native Americans and the Appalachian Mountain people was a matter of taste. It is a matter of science that the pawpaw is also nutritious. It has a vitamin and mineral profile that is close to that of the banana. The average pawpaw has about 80 kilocalories with 1.2 grams of protein and 18.8 grams of carbohydrates and 1.2 grams of fat (70 percent unsaturated). It is a particularly good source of vitamin C and potassium (about the same as a banana), with higher levels of the necessary minerals (calcium, phosphorous, magnesium, iron, zinc, copper and manganese) than apples, oranges or bananas; in addition, it has all of the essential amino acids. It is worthy of note that a wild fruit growing in a natural organic habitat produces an array of nutrients that is consistent with required animal sustenance. [14] Zebra swallowtail butterflies (Graphium marcellus) lay their eggs exclusively on pawpaw trees so that the hatched larvae will eat the leaves, thereby imparting a measure of toxicity to the adults to deter predation. The adult female butterflies have been observed to use only young leaves for their eggs, presumably to impart the maximum benefit of more concentrated chemical constituents. The larvae have developed a more direct means of protection. When disturbed by uninvited interlopers such as spiders or ants, they extend a specialized organ called an osmeterium that exudes offensive chemicals to drive them off. The alkaloids of the pawpaw are apparently as effective at convincing would –be predators that the Zebra swallowtail butterfly is not palatable as is the milkweed plant for the Monarch butterfly. [15]

Pawpaw is a case study of the medical assessment of indigenous plants based almost entirely on anecdote and empirical observation drawn from Native American tradition. The first official recorded exposition of the medicinal potential of pawpaw was the publication of Materia Medica Americana by David Schoepf in 1787 who offered that “A wine prepared from the unripe fruit is odorless and is highly useful in children’s sore mouth.” Dr. A. Clapp subsequently reported in Medicinal Plants of the United States published in 1850 that the ground up seeds of the pawpaw were used by Native Americans and subsequently by colonists as an insecticide, especially for the control of head lice. Since the fruits were widely consumed by Indians, it is likely that the copious large, discarded seeds were noted to repel insects which led ultimately to this etiology. However, the authors of the 1898 King’s American Dispensatory report that an experiment of the application of an aqueous preparation made from the seeds and applied to the heads of children at the Children’s Home of Cincinnati had no effect on the insects. The palliative properties of Pawpaw were also addressed in 1854 by John King in The American Eclectic Dispensary where he reported it to have emetic (vomit inducing) properties and that it was used as a tonic by the local country people.

The advent of modern science-based medicine in the late 19th century displaced quackery, innocent or otherwise, with its attendant snake oil purveyors. A bitter alkaloid was first isolated from pawpaw extracts and named asiminine after the genus Asimina by Curtis and John Lloyd in the 1884 Drugs and Medicines of North America. The 21st century has heralded burgeoning drugs for myriad ailments real, hypothesized and sometimes imagined. It has become increasingly apparent that nature is the fons et origo for chemical compounds to combat microbial insurgents; a renewed interest in the medicinal and pesticidal properties of pawpaw has ensued. A group of long chain fatty acids known as annonaceous acetogenins have been extracted from various parts of the tree; three compounds named asimicin, bullatacin and trilobacin show particular potency. As it turns out, the Native Americans were right, pawpaw is an effective and natural pesticide; a commercial product named Pawpaw Cell-Reg is sold commercially for this purpose. There is as yet no indication that it would be effective for head lice. Pawpaw may even have a role in the war on cancer. Research with the annonaceous acetogenins has demonstrated that these compounds act to limit the production of adenosine triphosphate (ATP), which is the primary source of cell energy. The tumor cells of cancer are problematic due to their rapid replication, which takes a lot of energy. The inhibition of ATP restricts the ability of the tumor to grow, as has been demonstrated in clinical trials [16].

Zebra Swallowtail butterflies (Graphium marcellus) lay their eggs exclusively on Pawpaw trees so that the hatched larvae will eat the leaves, thereby imparting a measure of toxicity to the adults to deter predation. The adult female butterflies have been observed to use only young leaves for their eggs, presumably to impart the maximum benefit of more concentrated chemical constituents. The larvae even have developed a more direct means of protection. When disturbed by uninvited interlopers such as spiders or ants, the larva extend a specialized organ called an osmeterium that exudes offensive chemicals to drive them off. The alkaloids of the Pawpaw are apparently as effective at convincing would –be predators that the Zebra swallowtail butterfly is not palatable as is the milkweed plant for the Monarch butterfly.

The chemical factory that operates sub rosa deep in the pawpaw patch took eons to build, random mutation by random mutation. It produced enough bitterness to keep the voracious bugs at bay long enough to grow, mature and reproduce; only the zebra swallowtail devised an antidote. It produced enough sweetness in a recognizable dollop to entice a trundling gomphothere to transport its seeds to establish new settlements as guarantors of perpetuity. In this it succeeded where the gomphothere failed. It all depended on the luck of a random mutation that conveyed resilience; most, like cancers, don’t. The pawpaw is unusual in that it evolved a big fruit for a big animal to do its bidding which could have resulted in colony collapse when they became scarce; humans may even have come to its rescue.

References:

1. http://www.pawpaw.kysu.edu/pawpaw/cooking.htm Kentucky State University cooperative has extensive information on pawpaw cultivars and nutrition.
2. http://www.henriettesherbal.com/eclectic.dmna/asimina/html
3. http://www.lewisandclarktrail.com/section1/kansascities/1806history2.htm
4. http://www.aihd.ku.edu/foods/Pawpaw.html
5. http://www.appalachianhistory.net/2015/09/way-down-yonder-in-paw-paw-patch.html
6. Wilson, M.F. and D.W. Schemske. 1980. “Pollinator limitation, fruit production, and floral display in pawpaw (Asimina triloba).” Bul. Torrey Bot. Club 107:401-408.
7. Meltzer, D. First Peoples in a New World, Colonizing Ice Age America, University of California Press, Berkeley, 2009. Pp 3-4, 44-48. This is an excellent source book for the archaeological evidence to date of pre-Columbian humans in the Americas.
8. Janzen, D and Martin. P 1982 “The Fruits that Gomphotheres Ate” Science Volume 215 no. 4528 pp 19-27.
9. Meltzer Op. cit. pp 239-320.
10. BBC (20 November 2003). “Scientists pinpoint dodo’s demise”. BBC News. London. Retrieved 10 July 2018.
11. Temple, S. A. (August 1977). “Plant-Animal Mutualism: Coevolution with Dodo Leads to Near Extinction of Plant”. Science. Volume 197 no.4306: pp 885–886.
12. Wilson, E. Op. cit. pp 79 – 102. Chapter Four is entitled The Planetary Killer.
13. http://www.pawpaw.kysu.edu/ – Kentucky State University has the only full-time research program for pawpaws in the world. Pawpaw research efforts are directed at improving propagation methods, developing orchard management recommendations, conducting regional variety trials, understanding fruit ripening and storage techniques, and germplasm collection and characterization of genetic diversity.
14. Jarvis, B. “Paper Tiger” The New Yorker 2 July 2018.
15. Hall D. and Butler J. ‘Zebra Swallowtail, Pawpaw Butterfly, Kite Swallowtail, Ajax Eurytides marcellus (Cramer) (Insecta: Lepidoptera: Papilionidae)” from the University of Florida Institute for Food and Agricultural Sciences at http://edis.ifas.ufl.edu/in215
16. Blossom, M “The Pawpaw, Asimina triloba” a full list of references is available at http://www.pawpaws.net/Pawpaw_Scientific_Paper.htm