Blueberry

Blueberries are blue because anthocyanin turns blue when the PH is basic – and to attract animals

Common Name: Blueberry, bilberry, whortleberry –  Blueberry would be a strong candidate for the most innocuous common name. Unlike many fruits called berry, the blueberry is true to its name. A true blue berry.  Bilberry is a European blueberry and a North American variant; whortleberry is of British origin.

Scientific Name: Vaccinium spp – The genus name was assigned by Carolinus Linnaeas in 1753 and is of obscure origin, possibly originating as an early Latin name for the bilberry or whortleberry but also implausibly from hyacinth, a member of the lily family native to the eastern Mediterranean region. Spp is an abbreviation meaning several species and is used whenever there is considerable variation due to hybridization as is the case with blueberries.[1]

Potpourri: Blueberries are the most dependable and commendable trailside fruit eaten as browse by hikers on the move.  In the fall as the trees and shrubs wrap up the annual cycle of flowering, growing, and seeding to pass the cold winter months in quiescent repose, the berries await their purposed fate. The upland woods where they mostly grow are awash in the reds of maples and the yellows of hickories in the canopy above the contrasting blues at their base that bring the joys of sweetness and not the doldrums of despair.  The three primary colors represent the fullness of the visual light spectrum and metaphorically the completeness of nature’s cycle. The fruit that bears the seeds of the next generation is the most important part of the plant. But there are many questions that arise: Why do the berries start out red and turn blue? Why do they grow where they do? Why are there so many of them when each seed contains all the DNA instructions necessary and sufficient for a whole new plant?  All in good time. 

There are two general types of blueberry. To be consistent with the hackneyed name of the fruit with a berry that is blue, the shrubs on which the blueberries grow are called highbush and lowbush (HW41 and Dubya43?). Both are grown commercially according to geographic climate preferences. That is far from the whole story of blueberry types, however, as there are myriad hybrids both between them and separately from each.  A recent scientific paper described the blueberry tribe Vaccinieae as a “large and morphologically diverse group that is widespread in the temperate and tropical zones of most continents.” DNA analysis was described as difficult because the characters normally used don’t work well. One of the reasons is that blueberries and their kin are not only diploid with two sets of chromosomes (like humans and many plants and animals), but also triploid, tetraploid, pentaploid … up to six sets or  hexaploid depending on the species.  It was concluded that the genus Vaccinium is not monophyletic, which means that there are multiple ancestors. For the purpose of a practical understanding of the habitat and range of the blueberry, highbush and lowbush will suffice. [2]  The highbush blueberry Vaccinium corymbosum is on the tall side at five to fifteen feet, a tree of a bush. The species name indicates that it grows in corymbs, which are clusters of flowers and then berries more or less in a planar array. They start out with a pinkish-red tinge that matures to fully white, producing a blue berry after pollination, a truly patriotic succession. The highbush blueberry of the dry upland areas in the Appalachian Mountains is the fons et origio of the commercial blueberries cultivated in the United States. [3]

Flowers must attract pollinators to make a fertile seeded blueberry fruit

Those who deprecate the federal government for its intrusion into local affairs should consider Frederick Vernon Coville, a botanist with the USDA who may be considered the progenitor of the commercial blueberry. In the introduction to the USDA bulletin written to document his research, he provides the rationale for his quest. A nine foot high, three inch diameter highbush blueberry transplanted on the grounds of the Smithsonian Institution in Washington DC had been there since before 1871 and was probably fifty years old. That this was not unique was confirmed at the Arnold Arboretum in Boston which a number of thirty year old blueberries that had been grown from seed or transplanted prior to 1880. However, it was also true that all  attempts to grow blueberry bushes using rich garden soils at agricultural research stations from Maine to Michigan had failed. [4]  Why the former and not the latter? What was the missing ingredient? Starting in 1906, Coville planted test plots with different combinations of soil and nutrients to discover four years later that the ingredient was acid … blueberries and a number of related ericaceous plants like cranberry and huckleberry required an acidic soil (PH < 7).  In 1911, he began a series of cross pollination experiments to create cultivars with attributes like larger, sweeter, and denser berry clusters. [5] His field notes, which are listed as collection 413 in the USDA archives, consist of daily penciled entries of research field varieties and fruiting quality. [6] This was the way gene modification was accomplished in the pre-CRISPR Cas-9 era. The historic trial and error method relies on random chance while the new method is scientific, putting the chosen gene in the right place. Unfortunately, the use of science to add genes to produce beneficial cultivars like higher nutrition and better drought tolerance earns the damning epithet GMO (genetically modified organisms) and us shunned by some as “Frankenfood.”

The lowbush blueberry Vaccinium angustifolium, referring to the narrow leaves which in Latin is angustus – folium … is literally diminutive in size at less than a foot. These are the dense berry thickets of New England and the Upper Midwest, notably Maine where it is the state berry ― blueberry pie is second only to lobster in defining the local cuisine. Called the late sweet blueberry in edible wild plant field guides, it was probably the most important fruit for Native Americans as one of the main ingredients for pemmican, a concoction of meat and berries that was a trail food staple. [7] The importance of the lowbush blueberry extended beyond edibility as Chippewa placed dried flowers on hot stones as a treatment for “craziness” and Iroquois used the berries in ceremony to invoke health and prosperity for the coming season. [8] Even though it readily hybridizes like its highbush cousin, the lowbush blueberry is more generally recognized by researchers as a single species that is highly polymorphic. The dense blueberry patches that occupy significant swaths of otherwise relatively sparse northern habitats are a major source of food for a wide variety of mammals and birds. Of particular note are black bears, whose reproductive success has been correlated to the size of the blueberry output in a given year, and large ground dwelling birds like wild turkeys and ruffed grouse. [9]

The lowbush blueberry patches dominate the landscape of Acadia in Maine

Why are blueberries blue? Bright red cranberries that are in the same genus grow in similar habitats. Everything in nature has a purpose ― in most cases related to Darwin’s epiphany that  survival is the outcome only if fit, meaning adaptable. Since fruits contain the seeds for future generations, fruit color must have evolved over time to attract animals as agents for transport. The animals in question  cannot have been  hunter gatherer H. sapiens since North America was devoid of hominids until about 12,000 years ago. While the determination of the responsible  animal is speculative, there are some interesting facts and correlations that provide a basis for hypothesis.  The first clue is that non-primate mammals cannot see red. The generally accepted reason is that the smell and hearing senses are much more important for survival in the brushy shadows of their habitats than sight. It is also reasoned that primate red vision was beneficial in locating ripe fruits in the jungle canopies of African forests; more food, more survivors. Birds also see red presumably for the same reason. It is demonstrably true that most berries are red and that avian dispersal is the primary vector for dissemination of the seeds of red-berried plants. A 2015 study compared the amount of berry seeds from 25 different plants (16 native and 9 invasive) in 450 bird dropping samples and found that birds ate almost exclusively from native plants. This can only  make sense if birds evolved eating native berries and that they would continue to do so, eschewing the invasives (which unfortunately does not seem to deter them much). [10] As an interesting correlation, the areas where cranberries predominate are in the same general area as the breeding ground for passenger pigeons. Though they are now extinct, having been extirpated by humans in the last century, a reasonable theory is that passenger pigeons ate cranberries and deposited the seeds all over their brooding areas, where the resultant cranberry bushes flourish.

Conversely, blueberries are not for the birds. This is not to say that birds won’t eat them  but only that bird consumption cannot have been the primary evolutionary forcing function … blueberries would have to be redberries. It is much more likely that blueberries became blue and sweet to attract mammals to propagate the seeds contained therein. A few observations again provide some basis for speculation. The first is that black bear fecundity, as pointed out above, correlates to the quantity of blueberries produced in any given year. Correlation is not causation but there is more. It is demonstrably true that the area of North America where black bears are indigenous is largely convergent with the natural habitat of the lowbush blueberry. It is also true that black bears eat a lot of berries, which can easily be verified by looking at bear scat encountered on the trail ― invariably dotted with seeds. In my view, black bears or perhaps their evolutionary ancestors are the best candidate as the original  blueberry propagator. That would also help to explain why there are so many berries … it takes a lot of berries to attract a bear.

One of nature’s more interesting innovations is how the color of a fruit is controlled to attract an animal. Anthocyanins are complex chemical compounds produced by some plants for which they perform no other function but pigmentation. Like litmus paper, acidic environments cause red pigmentation and  basic means blue. Anthocyanin is what makes roses red, violets blue, and plums purple. It is also the source of the brilliant colors of red and sugar maples in autumn.  Here however, red has purpose which is thought to shield individual leaves from damaging infrared radiation in early fall so that more nutrients can be retained in the roots over winter.  It is interesting to note that blueberries start out pinkish-red and gradually become blue as they ripen and thereafter are ready to eat. Coville demonstrated that blueberry bushes grow in acidic soil, so clearly the chemistry of the plant is on the red or acidic side. This is amply demonstrated in the fall, when blueberry bushes turn brilliant red, indicating that they produce copious amounts of anthocyanin and that they are acidic. [11] Blueberries must therefore be turned blue by the plant which can only be achieved with high PH or basic chemicals that must be produced for this purpose – to attract bears.

Commercially grown blueberries in the form of both V. angustifolium and the cultivars that originated with V. corymbosum are second only to strawberries in quantity and value with annual sales of nearly $1B. Cranberries (V. macrocarpon) which are also heath family plants closely related to blueberries, are equally popular but almost wholly as juice and the essential holiday sauce. Raspberries and blackberries are at the back of the pack. But here we are literally talking apples and oranges. The botanical berry has little to do with the vernacular use of the term. A berry is defined as a fleshy fruit with seeds embedded in the pulp, like blueberries, huckleberries and even tomatoes and watermelons. The strawberry is an accessory fruit with the seeds embedded in the external skin of the fruit and both raspberries and blackberries are aggregates, consisting of many tiny berries clustered together. The natural foods movement gained ground at the turn of the millennium in reaction to the realization that processed food consumption had resulted in an epidemic of obesity according to both the CDC and NIH. Blueberries were among the more favored foods in the fruit and vegetable category that emerged as the gold standard for a healthy diet. Domestic production consequently rose 284 percent between 2000 and 2019 supplemented by South American imports that rose 1000 percent during that same period for blueberries year round. [12] In that nature operates according to opportunistic species seeking perpetuation and dominance, the large numbers of nutritive blueberries were ripe for exploitation by a fungus appropriately named Monilinia vaccinii-corymbosi for its assault on the species. It can destroy over 50 percent of the crop (85% in New Hampshire in 1974). The infected fruit goes by the pejorative mummy berry for the swollen wrinkled and gray blobs that result. [13]

Blueberries are good food for all animals,  not just bears. High levels of vitamin C vitamin K, and manganese are conveniently packaged with high fiber, the stuff of proper stools.  More importantly from the health standpoint, blueberries have exceptional levels of flavonoids, notably anthocyanins … more than cranberries, strawberries, plums and most other fruits. Flavonoid compounds  are for the most part considered  beneficial for health  due to antioxidant and anti-inflammatory activity. The arrant actor is the free radical, a malevolent name for an insidious chemical. Simply put, it is any chemical element that is either missing one electron or has one too many. Since chemistry abhors untidy stray charges in favor of the neutral state, free radicals seek to balance their electrical charge by reacting with anything available, like body cells and the DNA that they all contain. Disrupted DNA mostly results in cell death but certain mutations can have more inimical effects, like the uncontrolled growth of a cancerous tumor. Antioxidant chemicals are in their most general form hydrogen donors that combine and neutralize free radicals. Recent studies have cast some doubt on the role of anthocyanin as an effective antioxidant. However, the benefits of blueberries as part of a healthy diet are indisputable. The only question is why. Affirmed  benefits of blueberries for human health. include reducing cognitive degeneration, promoting heart health, reducing susceptibility to cancer, and lowering blood pressure, among many others. [14]   

So why are blueberries blue? Because they contain anthocyanin in an aqueous environment with  a high enough PH so they are basic blue in lieu of acidic red. This requires a certain amount of finesse since the bush on which they grow is rooted in acidic soil with  acidic leaves marked by the red of the same anthocyanin chemistry. But that is not really why blueberries are blue but rather how they became blue. Why they are blue is because that was the best color to attract an animal with enough drawing power and consistency to propagate the species. They are blue because they are in the ecosystem of which they are but one of the many interconnected parts.   

References:   

1.  https://naturalhistory2.si.edu/botany/ing/genusSearchTextMX.cfm  

2. Kron, K. et al  “Phylogenetic relationships within the blueberry tribe (Vaccinieae, Ericaceae) based on sequence data from MATK and nuclear ribosomal ITS regions, with comments on the placement of Satyria”. American Journal of Botany. February 2002 Volume  89 Number 2 pp 327–336.

3. Niering, W. and Olmstead, N. National Audubon Society Field Guide to North American Wildflowers, Alfred A. Knopf, New York, 1998, pp 508-509

4. Coville, F. Experiments in Blueberry Culture. US Government Printing Office. 1910.

5. https://federallabs.org/successes/success-stories/blueberries-making-a-superb-fruit-even-better  

6. https://www.nal.usda.gov/speccoll/collectionsguide/collection2.php?search=coville

7. Elias T. and Dykeman, P. Edible Wild Plants, A North American Field Guide, Sterling Publishing New York, 1990, pp 164 – 167.

8. Ethnobotany data base http://naeb.brit.org/uses/search/?string=vaccinium

9. https://www.fs.fed.us/database/feis/plants/shrub/vacang/all.html     

10. Runwal, P. “Migratory Birds like Native Berries Best.” Audubon Magazine, 12 June 2020

11. Wilson, C, and Loomis, W. Botany, 4th Edition. Holt, Rinehart, and Winston, New York, 1967,  pp.52-53.

12. https://www.ers.usda.gov/data-products/charts-of-note/charts-of-note/?topicId=14849     

13. Batra, L. “Monilinia vaccinii-corymbosi (Sclerotiniaceae)”Its biology on blueberry and other related species” Mycologia  Volume 75 number 1 1985 pp 131-152.

14. https://www.ars.usda.gov/plains-area/gfnd/gfhnrc/docs/news-2014/blueberries-and-health/

2 thoughts on “Blueberry

  1. Really fascinating article, thanks! Hey, are you a Sierra Club Outings leader by any chance? Would you be interested in leading a fall winter hike with someone who is a leader? Thanks, Lily [image: photo] *Lily Fountain * *pronouns: she/her/hers* *Cell: *301-442-5854 *lily.fountain@mdsierra.org * *Chair, Natural Places Committee * *https://www.sierraclub.org/maryland/committees#NaturalPlaces * https://www.sierraclub.org/maryland/preserving-natural-places *Maryland Sierra Club *PO Box 278 Riverdale, MD 20738 652‬

    On Tue, Nov 9, 2021 at 12:31 PM Hiker’s Notebook wrote:

    > hikersnotebook posted: ” Blueberries are blue because anthocyanin turns > blue when the PH is basic – and to attract animals Common Name: Blueberry, > bilberry, whortleberry – Blueberry would be a strong candidate for the > most innocuous common name. Unlike many fruits calle” >

    Like

    1. I have been a hike leader since 1995 with the Sierra Club which was MWROP and is now SCPRO (Sierra Club Potomac Regional Outings). I am now leading hikes monthly with Larry Broadwell as part of a series to advertise the latest PATC hiking guide from Montgomery and Frederick Counties. I am not sure what you have in mind with leading with a leader but I am supportive of doing this, but only during the week, not on a weekend. We have met through Marc Imlay on fungal matters.

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