Cranberries are a staple in U.S. households at Thanksgiving – but how did this bog dweller end up on holiday tables?

Compared to many valuable plant species that were domesticated over thousands of years, cultivated cranberry (Vaccinium macrocarpon) is a young agricultural crop, just as the U.S. is a young country and Thanksgiving is a relatively new holiday. But as a plant scientist, I’ve learned much about cranberries’ ancestry from their botany and genomics.

New on the plant breeding scene

Humans have cultivated sorghum for some 5,500 years, corn for around 8,700 years and cotton for about 5,000 years. In contrast, cranberries were domesticated around 200 years ago – but people were eating the berries before that.

Wild cranberries are native to North America. They were an important food source for Native Americans, who used them in puddings, sauces, breads and a high-protein portable food called pemmican – a carnivore’s version of an energy bar, made from a mixture of dried meat and rendered animal fat and sometimes studded with dried fruits. Some tribes still make pemmican today, and even market a commercial version.

Cranberry cultivation began in 1816 in Massachusetts, where Revolutionary War veteran Henry Hall found that covering cranberry bogs with sand fertilized the vines and retained water around their roots. From there, the fruit spread throughout the U.S. Northeast and Upper Midwest.

Today, Wisconsin produces roughly 60% of the U.S. cranberry harvest, followed by Massachusetts, Oregon and New Jersey. Cranberries also are grown in Canada, where they are a major fruit crop.

A flexible and adaptable plant

Cranberries have many interesting botanical features. Like roses, lilies and daffodils, cranberry flowers are hermaphroditic, which means they contain both male and female parts. This allows them to self-pollinate instead of relying on birds, insects or other pollinators.

A cranberry blossom has four petals that peel back when the flower blooms. This exposes the anthers, which contain the plant’s pollen. The flower’s resemblance to the beak of a bird earned the cranberry its original name, the “craneberry.”

When cranberries don’t self-pollinate, they rely on bumblebees and honeybees to transport their pollen from flower to flower. They can also be propagated sexually, by planting seeds, or asexually, through rooting vine cuttings. This is important for growers because seed-based propagation allows for higher genetic diversity, which can translate to things like increased disease resistance or more pest tolerance.

Asexual reproduction is equally important, however. This method allows growers to create clones of varieties that perform very well in their bogs and grow even more of those high-performing types.

Every cranberry contains four air pockets, which is why they float when farmers flood bogs to harvest them. The air pockets also make raw cranberries bounce when they are dropped on a hard surface – a good indicator of whether they are fresh.

These pockets serve a biological role: They enable the berries to float down rivers and streams to disperse their seeds. Many other plants disperse their seeds via animals and birds that eat their fruits and excrete the seeds as they move around. But as anyone who has tasted them raw knows, cranberries are ultra-tart, so they have limited appeal for wildlife.

Reading cranberry DNA

For cranberries being such a young crop, scientists already know a lot about their genetics. The cranberry is a diploid, which means that each cell contains one set of chromosomes from the maternal parent and one set from the paternal parent. It has 24 chromosomes, and its genome size is less than one-tenth that of the human genome.

Insights like these help scientists better understand where potentially valuable genes might be located in the cranberry genome. And diploid crops tend to have fewer genes associated with a single trait, which makes breeding them to emphasize that trait much simpler.

Researchers have also described the genetics of the cultivated cranberry’s wild relative, which is known as the “small cranberry” (Vaccinium oxycoccos). Comparing the two can help scientists determine where the cultivated cranberry’s agronomically valuable traits reside in its genome, and where some of the small cranberry’s cold hardiness might come from.

Researchers are developing molecular markers – tools to determine where certain genes or sequences of interest reside within a genome – to help determine the best combinations of genes from different varieties of cranberry that can enhance desired traits. For example, a breeder might want to make the fruits larger, more firm or redder in color.

While cranberries have only been grown by humans for a short period of time, they have been evolving for much longer. They entered agriculture with a long genetic history, including things like whole genome duplication events and genetic bottlenecks, which collectively change which genes are gained or lost over time in a population.

Whole genome duplication events occur when two species’ genomes collide to form a new, larger genome, encompassing all the traits of the two parental species. Genetic bottlenecks occur when a population is greatly reduced in size, which limits the amount of genetic diversity in that species. These events are extremely common in the plant world and can lead to both gains and losses of different genes.

Analyzing the cranberry’s genome can indicate when it diverged evolutionarily from some of its relatives, such as the blueberry, lingonberry and huckleberry. Understanding how modern species evolved can teach plant scientists about how different traits are inherited, and how to effectively breed for them in the future.

Ripe at the right time

Cranberries’ close association with Thanksgiving was simply a practical matter at first. Fresh cranberries are ready to harvest from mid-September through mid-November, so Thanksgiving falls within that perfect window for eating them.

Cranberry sauce was first loosely described in accounts from the American colonies in the 1600s, and appeared in a cookbook for the first time in 1796. The berries’ tart flavor, which comes from high levels of several types of acids, makes them more than twice as acidic as most other edible fruits, so they add a welcome zing to a meal full of blander foods like turkey and potatoes.

In recent decades, the cranberry industry has branched out into juices, snacks and other products in pursuit of year-round markets. But for many people, Thanksgiving is still the time when they’re most likely to see cranberries in some form on the menu.

Serina DeSalvio ne travaille pas, ne conseille pas, ne possède pas de parts, ne reçoit pas de fonds d'une organisation qui pourrait tirer profit de cet article, et n'a déclaré aucune autre affiliation que son organisme de recherche.

Autumn is the season to gaze at gorgeous leaves of gold, yellow and orange as they flutter from the trees and fall on our yards – but then, of course, comes the tedious task of raking them up and trying to decide what to do with them. SciLine interviewed Susan Barton, a professor of plant and soil sciences at the University of Delaware, who says taking a lazy approach is actually a win for your garden and the critters that live there.

Below are some highlights from the interview. Answers have been edited for brevity and clarity.

Can leaves on a landscaped property ever be left as they are, or should they always be mulched?

Susan Barton: A layer of leaves on the lawn will exclude light, which would be detrimental to the lawn. So when the leaves fall, either rake them up or chop them up with a lawn mower so they are finer and can sift down in through the grass blades. But if they fall in a landscape bed, or under trees, shrubs and larger plants, it’s fine to just leave the leaves without mulching them.

What are the benefits of mulching leaves rather than removing them?

Susan Barton: The leaves contain nutrients, and they also are a source of organic matter. So if you allow the leaves to go back into the landscape, you are providing nutrients for the plants to take up, and you are providing organic matter that will improve the soil structure.

If you think about forest, where leaves just naturally return to the soil and decompose every year, it’s some of the richest soil we have. By allowing that to happen in your landscape beds, you’re getting the same benefits.

What can keep leaves from blowing from one property to another?

Susan Barton: Chopping them up will dramatically reduce the blowing of the leaves. Make them smaller by either mowing over the leaves where they fall in the lawn, or raking them into piles and then mowing them.

There are also leaf vacuums that vacuum, chop up and put the leaves in a bag. Then you spread the leaves on your landscape beds.

What are the environmental benefits of not removing the leaves?

Susan Barton: If you rake up your leaves, put them in a black plastic bag and have them taken off to a landfill, then they never get to decompose and return those nutrients and organic matter back to the soil. Instead, you’re taking what could be a resource and making it a problem.

Also, many insects spend the winter in leaf litter. And a lot of people might not want insects in their landscape, but only about 2% of all the insects in the world are considered pests. Most of them are either beneficial or of no consequence to humans, and they are very important food sources for birds and other animals. Birds feed the insects, especially caterpillars, to their hatchlings.

So by allowing the insects to overwinter in the leaf litter, you’re supporting bird populations and, of course, pollinators, which help plants produce seeds that can develop into new plants.

When should people fertilize lawns?

Susan Barton: In the fall, because that is when turf grass is primarily growing roots and you’re promoting the kind of grass growth that makes a healthy, dense lawn. When you fertilize in the spring, your grass is growing leaves at that point, so you’re really just causing the grass to grow more and grow faster, and you will need to mow more often. So it really doesn’t make sense to fertilize in the spring.

Also, when you chop up the leaves in the fall, you are actually also fertilizing in the fall because you’re putting those chopped up leaves back into the soil. But it’s a good idea to add some additional fertilizer besides just the leaf litter.

How can people get the most out of their lawns and make their landscaping more environmentally friendly?

Susan Barton: The suburban norm is to have a lawn with some decorative plants around the house, or at the end of the driveway. But I think it’s a good idea to sort of flip that paradigm and design areas of the lawn that provide for play and gathering spaces, and then figure out what everything else can be.

It’s just a different way of thinking about the landscape, and much more environmentally sensitive. It will provide all kinds of ecosystem services, whether it’s better water infiltration or better air quality. If we think about pulling carbon dioxide out of the air, we’re doing it a lot more if we’ve got a ground cover, a shrub layer, a small tree layer and a large tree layer than we are if we have just a lawn.

Watch the full interview to hear more.

SciLine is a free service based at the nonprofit American Association for the Advancement of Science that helps journalists include scientific evidence and experts in their news stories.

Susan Barton does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.

The annual United Nations Climate Change Conference, better known as COP, that starts Nov. 30 in the United Arab Emirates will bring together governments, businesses, international organizations and NGOs to shine a spotlight on the climate emergency the world faces and consider solutions to the crisis. The alarming rates at which we are losing species is not just a tragedy of epic proportions – the destruction of biodiversity also robs humanity of one of its strongest defenses against climate change.

Retaining the earth’s diverse mix of animals and plants is crucial for the planet’s future, yet any plan to halt its loss must grapple with the reality that not every species can be saved from extinction because of the limited resources we have for biodiversity conservation. By one estimate, about US$598 billion to $824 billion is needed annually to reverse the loss of species worldwide.

Different ways of posing the problem

Given finite research and practical resources, how should we act to conserve biological diversity? Should we, as I have argued in my research as an expert in environmental economics, try to regulate the rate at which habitat is being converted from natural to human-centered uses?

An alternative approach concentrates on conserving what biologists call keystone species that play a critical role in holding the ecosystem together. An example is the gray wolf in Yellowstone National Park, whose presence regulates prey populations like elk and deer, which in turn have cascading effects on vegetation and the overall ecosystem structure and function.

The Bible suggests a contrasting approach in the Lord’s dictum to Noah before the great flood: “Of fowls after their kind, and of cattle after their kind, of every creeping thing of the earth after his kind, two of every sort shall come unto thee, to keep them alive.”

A solution

One of the most original and interesting answers to this question was provided by the late Harvard economist Martin Weitzman, who applied economic analysis to address the conservation of endangered species. In a pioneering 1998 paper titled The Noah’s Ark Problem, Weitzman viewed the challenge of figuring out which species to conserve with limited resources as a modern-day equivalent of the problem the biblical patriarch Noah faced when trying to determine what to take with him – and hence save – on his ark.

In Weitzman’s view, biodiversity gives rise to two kinds of values. The first is utility to humans – insects pollinate crops that yield food, and so on. There is no serious dispute that biodiversity – the variety of living species on Earth, including plants, animals, bacteria and fungi – benefits humans.

As the World Health Organization puts it, “Healthy communities rely on well-functioning ecosystems. They provide clean air, fresh water, medicines and food security. They also limit disease and stabilize the climate.” Yet nearly a third of all monitored species are currently endangered because of human activities.

The second kind identified by Weitzman is the inherent value of the wide variety of species and the genetic information they contain to biological diversity itself. Biodiversity plays a crucial role in maintaining the stability and resilience of ecosystems.

For example, increased genetic variation is important to wild Alaskan salmon returning to natal streams and rivers to reproduce. Populations in different streams have developed different sets of genetic information; some of these will allow for the earlier migration in streams that will be needed under warming temperatures and earlier snowmelt.

Weitzman likens the task of preserving different species to the task of saving the volumes in a library that represent an accumulation of human knowledge.

While in principle, every volume in the library might be valuable, some may have information that is also available in other libraries. Therefore, the objective would be to save those volumes that have information in them that is not contained anywhere else. According to this view, a conservationist’s goal ought to be to save as much of this genetic information as possible, even if the species concerned provide little direct value to humans.

This line of thinking provides counterintuitive guidance to conservationists. Specifically, it suggests that the best way to conserve biodiversity in an uncertain and resource-constrained world is to pick a species and then save as many members of this species as possible. By following this aggressive or “extreme policy,” the conservationist preserves not only what is informationally distinct about this species but also all the information it shares with other species.

An example

To see this, imagine that there are two libraries that have many volumes (or species members), some unique to each library and some overlapping. If Library 1 burns to the ground, we lose all of the volumes (species members) with the exception of those that are also housed in Library 2. The same is true if Library 2 burns.

If both libraries burn, all is lost. If both are on fire, and we do not have the equipment to save both, and one library takes fewer resources to save, we may be better off using our scarce resources to protect that one and letting the other one go in order to preserve the unique volumes (species members) as well as the knowledge in the overlapping volumes.

What does it mean in practice?

The practical meaning is that – when forced to choose – it may not make much sense to use limited conservation funds to protect a highly endangered species such as cuddly pandas that are very expensive to protect. We may be better off protecting, for example, the Atlantic menhaden, or pogy, a primary food source for bigger fish and birds along the Eastern Seaboard and a vital connection between the bottom and top of the food chain. A current lawsuit claims it is subject to overfishing in and around the Chesapeake Bay.

Weitzman’s Noah’s Ark model seeks to provide useful guidance in determining how to prioritize our efforts to save endangered species, with the presumption that biodiversity is both of value to humans and that it is inherently valuable. While we lack the resources to save every at-risk species from extinction, further delay in dealing with the climate emergency and its harmful effects on the loss of species is one thing the world cannot afford.

Amitrajeet A. Batabyal does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.