Year of Pollination: Pollination Syndromes and Beyond

A discussion of pollination syndromes should begin with the caveat that they are a largely outdated way to categorize plant-pollinator interactions. Still, they are important to be aware of because they have informed so much of our understanding about pollination biology, and they continue to be an impetus for ongoing research. The concept of pollination syndromes exists in part because we are a pattern seeking species, endeavoring to place things in neat little boxes in order to make sense of them. This is relatively easy to do in a hypothetical or controlled environment where the parameters are selected and closely monitored and efforts are made to eliminate noise. However, the real world is considerably more dynamic than a controlled experiment and does not conform to black and white ways of thinking. Patterns are harder to unveil, and it takes great effort to ensure that observed patterns are genuine and not simply imposed by our pattern seeking brains.

That being said, what are pollination syndromes?  Pollination syndromes are sets of floral traits that are thought to attract specific types of pollinators. The floral traits are considered to have evolved in order to appeal to a particular group of pollinators – or in other words, selective pressures led to adaptations resulting in mutualistic relationships between plants and pollinators. Pollination syndromes are examples of convergent evolution because distantly related plant species have developed similar floral traits, presumably due to similar selection pressures. Pollination syndromes were first described by Italian botanist, Federico Delpino, in the last half of the 19th century. Over several decades his rudimentary ideas were fleshed out by other botanists, resulting in the method of categorization described (albeit briefly) below.

Honey bee on bee's friend (Phacelia tanacetifolia)

A honey bee getting friendly with bee’s friend (Phacelia tanacetifolia)

Pollination by bees (melittophily) – Flowers are blue, purple, yellow, or white and usually have nectar guides. Flowers are open and shallow with a landing platform. Some are non-symmetrical and tubular like pea flowers. Nectar is present, and flowers give off a mild (sometimes strong) sweet scent.

Pollination by butterflies (psychophily) – Flowers are pink, purple, red, blue, yellow, or white and often have nectar guides. They are typically large with a wide landing pad. Nectar is inside a long, narrow tube (or spur), and flowers have a sweet scent.

Pollination by hawkmoths and moths (sphingophily and phalaenophily) – Moth pollinated flowers open at night, have no nectar guides, and emit a strong, sweet scent. Flowers pollinated by hawkmoths are often white, cream, or dull violet and are large and tubular with lots of nectar. Those pollinated by other moths are smaller, not as nectar rich, and are white or pale shades of green, yellow, red, purple, or pink.

Pollination by flies (myophily or sapromyophily) – Flowers are shaped like a basin, saucer, or kettle and are brown, brown-red, purple, green, yellow, white, or blue.  Some have patterns of dots and stripes. If nectar is available, it is easily accessible. Their scent is usually putrid. A sapromyophile is an organism that is attracted to carcasses and dung. Flies that fall into this category visit flowers that are very foul smelling, offer no nectar reward, and essentially trick the fly into performing a pollination service.

Pollination by birds (ornithophily) –  Flowers are usually large, tubular, and red, orange, white, blue, or yellow. They are typically without nectar guides and are odorless since birds don’t respond to scent. Nectar is abundant and found at various depths within the flower.

Pollination by bats (chiropterophily) – Flowers are large, tubular or bell shaped, and white or cream colored with no nectar guides. They open at night, have abundant nectar and pollen, and have scents that vary from musty to fruity to foul.

Pollination by beetles (cantharophily) – Flowers are large and bowl shaped and green or white. There are no nectar guides and usually no nectar. The scent is strong and can be fruity, spicy, or putrid. Like flies, some beetles are sapromyophiles.

Locust borer meets rubber rabbitbrush (Ericameria nauseosa)

A locust borer meets rubber rabbitbrush (Ericameria nauseosa)

In addition to biotic pollination syndromes, there are two abiotic pollination syndromes:

Pollination by wind (anemophily) – Flowers are miniscule and brown or green. They produce abundant pollen but no nectar or odor. The pollen grains are very small, and the stigmas protrude from the flower in order to capture the windborne pollen.

Pollination by water (hydrophily) –  Most aquatic plants are insect-pollinated, but some have tiny flowers that release their pollen into the water, which is picked up by the stigmas of flowers in a similar manner to plants with windborne pollen.

This is, of course, a quick look at the major pollination syndromes. More complete descriptions can be found elsewhere, and they will differ slightly depending on the source. It’s probably obvious just by reading a brief overview that there is some overlap in the floral traits and that, for example, a flower being visited by a bee could also be visited by a butterfly or a bird. Such an observation explains, in part, why this method of categorizing plant-pollinator interactions has fallen out of favor. Studies have been demonstrating that this is not a reliable method of predicting which species of pollinators will pollinate certain flowers. A close observation of floral visitors also reveals insects that visit flowers to obtain nectar, pollen, and other items, but do not assist in pollination. These are called robbers. On the other hand, a plant species may receive some floral visitors that are considerably more effective and reliable pollinators than others. What is a plant to do?

Pollination syndromes imply specialization, however field observations reveal that specialization is quite rare, and that most flowering plants are generalists, employing all available pollinators in assisting them in their reproduction efforts. This is smart, considering that populations of pollinators fluctuate from year to year, so if a plant species is relying on a particular pollinator (or taxonomic group of pollinators) to aid in its reproduction, it may find itself out of luck. Considering that a flower may receive many types of visitors on even a semi-regular basis suggests that the selective pressures on floral traits may not solely include the most efficient pollinators, but could also include all other pollinating visitors and, yes, even robbers. This is an area where much more research is needed, and questions like this are a reason why pollination biology is a vibrant and robust field of research.

A bumble bee hugs Mojave sage (Salvia pachyphylla)

A bumble bee hugs the flower of a blue sage (Salvia pachyphylla)

Interactions between plants and pollinators is something that interests me greatly. Questions regarding specialization and generalization are an important part of these interactions. To help satiate my curiosity, I will be reading through a book put out a few years ago by the University of Chicago Press entitled, Plant-Pollinator Interactions: From Specialization to Generalization, edited by Nickolas M. Waser and Jeff Ollerton. You can expect future posts on this subject as I read through the book. To pique your interest, here is a short excerpt from Waser’s introductory chapter:

Much of pollination biology over the past few centuries logically focused on a single plant or pollinator species and its mutualistic partners, whereas a focus at the level of entire communities was uncommon. Recently we see a revival of community studies, encouraged largely by new tools borrowed from the theory of food webs that allow us to characterize and analyze the resulting patterns. For example, pollination networks show asymmetry – most specialist insects visit generalist plants, and most specialist plants are visited by generalist insects. This is a striking departure from the traditional implication of coevolved specialists!

References:

Texas State Flower

The state flower of Texas blooms in early spring. At least most of them do anyway. Some don’t bloom until late spring and others bloom in the summer. The reason for the staggered bloom times is that the state flower of Texas is not one species but six. All are affectionately referred to as bluebonnets and all are revered by Texans.

As the story goes, at the beginning of the 20th century the Texas legislature set out to determine which flower should represent their state. One suggestion was the cotton boll, since cotton was a major agricultural crop at the time. Another suggestion was a cactus flower, because cacti are common in Texas, are long-lived, and have very attractive flowers. A group of Texas women who were part of the National Society of Colonial Dames of America made their pitch for Lupinus subcarnosus, commonly known as buffalo clover or bluebonnet. Ultimately, the nomination from the women’s group won out, and bluebonnets became an official state symbol.

The debate didn’t end there though. Many people thought that the legislature had selected the wrong bluebonnet, and that the state flower should be Lupinus texensis instead. Commonly known as Texas bluebonnet, L. texensis is bigger, bolder, and more abundant than the comparatively diminutive L. subcarnosus. This debate continued for 70 years until finally the legislature decided to solve the issue by including L. texensis “and any other variety of bluebonnet not heretofore recorded” as the state flower of Texas.

Lupinus texensis - Texas bluebonnet

Lupinus texensis (Texas bluebonnet) bravely growing in Idaho

According to Mr. Smarty Plants, the list of Texas state flowers includes (in addition to the two already mentioned)  L. perennis, L. havardii, L. plattensis, and L. concinnus. Most on this list are annuals, and all are in the family Fabaceae – the pea family. Plants in this family are known for their ability to convert atmospheric nitrogen into plant available nitrogen with the help of a soil dwelling bacteria called rhizobia. The genus Lupinus includes over 200 species, most of which are found in North and South America. Others occur in North Africa and the Mediterranean. Plants in this genus are popular in flower gardens, and there are dozens of commercially available hybrids and cultivars.

L. subcarnosus is sometimes referred to as sandy land bluebonnet and occurs mainly in sandy fields and along roadsides. L. texensis is a Texas endemic; its native range includes the prairies and open fields of north and south central Texas. It is now found throughout Texas and bordering states due to heavy roadside plantings. L. perennis is the most widespread Texas bluebonnet, occurring throughout the eastern portion of the U.S. growing in sand hills, woodland clearings, and along roadsides. L. havardii is the largest of the Texas bluebonnets. It has a narrow range, and is found in a variety of soil types.  L. plattensis is a perennial species and occurs in the sandy dunes of the Texas panhandle. L. concinnus is the smallest of the Texas bluebonnets and is found mainly in sandy, desert areas as well as some grasslands.

Lupinus concinnus (...) - photo credit: www.eol.org

Lupinus concinnus (Nipomo Mesa lupine) – photo credit: www.eol.org

A legend surrounds the rare pink bluebonnet.

A legend surrounds the rare pink bluebonnet

Read more about Texas bluebonnets here and here.

“I want us to know our world. If I lived in north Georgia on up through the Appalachians, I would be just as crazy about the mountain laurel as I am about bluebonnets.” – Lady Bird Johnson

Field Trip: Lady Bird Johnson Wildflower Center, part two

This is the second in a series of two posts about my recent trip to Lady Bird Johnson Wildflower Center in Austin, Texas. You can read the first post here. Both posts are comprised of mostly pictures, as they tell a much better story about the place then my words can. However, even pictures don’t do the place justice; it’s definitely a site that you are going to have to see for yourself. I highly recommend it.

One name that kept coming up during the native plant conference was Doug Tallamy – and for good reason. Tallamy has long promoted and encouraged the use of native plants in landscapes, largely for the creation of wildlife habitat in urban and suburban areas. In 2007 he put out a book entitled, Bringing Nature Home: How You Can Sustain Wildlife with Native Plants, in which he made a strong argument for native plant gardens. His book and lectures have inspired many to seek out native plants to include in their yards. What was lacking in his book, however, was detailed information on the horticulture and design aspects of using native plants. So in 2014, together with Rick Darke, Tallamy put out The Living Landscape, an impressive tome outlining how to create beautiful and functional gardens using native plants. Both books are well worth your time.

The plant name following each photo or series of photos links to a corresponding entry in the Native Plant Database which is managed by the Wildflower Center’s Native Plant Information Network. The quotes that accompany the plant names are taken from the Native Plant Database entries.

Ilex vomitoria (yaupon). “The leaves and twigs contain caffeine, and American Indians used them to prepare a tea which they drank in large quantities ceremonially and then vomited back up, lending the plant its species name, vomitoria. The vomiting was self-induced or because of other ingredients added; it doesn’t actually cause vomiting.”

aesculus pava var pava 3

Aesculus pavia var. pavia (red buckeye). “Long popular for its brilliant, hummingbird-attracting spring flowers and rich green foliage, it is found in nature most often as a plant of woodland edges, where it can get morning sun and afternoon shade.”

tillandsia recurvata 5

Tillandsia recurvata (ball moss). An epiphyte commonly found on trees within its range, including Quercus fusiformis (escarpment live oak) a dominant tree at the Wildflower Center. “Some have been introduced into other warm regions and cultivated for use as ornamentals or for their edible fruit.”

Opuntia ellisiana (spineless prickly pear). A spineless form of Opuntia cacanapa derived from cultivation. “The spineless prickly pear is a great addition to the landscape for those seeking a cactus form, showy blooms, and bright red cactus fruits (tunas). Beware, although it doesn’t have long sharp spines, the tiny glochids (slivers) are very irritating to the skin if the plant is not handled correctly.”

Gelsemium sempervirens (Carolina jessamine). “The flowers, leaves, and roots are poisonous and may be lethal to humans and livestock. The species nectar may also be toxic to honeybees if too much is consumed, and honey made from Carolina jessamine nectar may be toxic to humans.”

Lonicera sempervirens (coral honeysuckle). “Flowers attract hummingbirds, bees, and butterflies. Fruits attract quail, purple finch, goldfinch, hermit thrush, and American robin.”

windmill

Field Trip: Lady Bird Johnson Wildflower Center, part one

Last week my place of employment sent me to Austin, Texas to spend some time at the Lady Bird Johnson Wildflower Center. I was there for a native plant conference put on by the American Public Garden Association. I had been wanting to visit the Wildflower Center for a long time, so it was great to finally get the chance. Their gardens are truly amazing. I spent three days there, but could have easily stayed much longer. The native plant conference was great, too. I learned a lot about native plant horticulture, and I left feeling inspired to put those things into practice. If you are wondering “why native plants?,” the Wildflower Center has a good answer to that on their website.

While I was there I took dozens of photos, so I am sharing some of those with you in a two part post. The plant name following each photo or series of photos links to a corresponding entry in the Native Plant Database which is managed by the Wildflower Center’s Native Plant Information Network. The quotes that accompany the plant names are taken from the Native Plant Database entries.

Sophora secundiflora (Texas mountain laurel). “The fragrance of Texas mountain laurel flowers is reminiscent of artificial grape products.”

Ranunculus macranthus (large buttercup). “This is one of the largest flowered native buttercups. The large butter-yellow flowers and attractive foliage of this plant immediately attract the eye.”

echinocereus reichenbachii 3

Echinocereus reichenbachii (lace cactus). “Lace cactus is unpredictable in its development, one plant forming a single stem, while its neighbor may branch out and form a dozen or more.”

Dalea greggii (Gregg’s prairie clover). “Grown mostly for its silvery, blue-green, delicately compound leaves, the shrub is awash with clusters of tiny, pea-shaped, purple flowers in spring and early summer.” 

viburnum rufidulum 5

Viburnum rufidulum (southern blackhaw). “In Manual of the Vascular Plants of Texas, Correll and Johnston noted that the fruit tastes similar to raisins.”

mahonia trifoliata 5

Mahonia trifoliolata (agarita). “Songbirds eat the fruits, and quail and small mammals use the plant for cover. It is considered a good honey source.”

lady bird johnson quote

How Pitcher Plants Eat Bugs (Frog Optional)

SAMSUNG

A few months ago at work I captured this photo of a frog inside of a pitcher plant. Do you see it? It is pretty well camouflaged and poking its head out just enough to intercept curious insects lured in by the promise of nectar, eating them before they can make their way into the tube. Either way, approaching insects are about to meet their fate. Whether by plant or by frog, they are destined to be consumed lest they turn away in time.

This frog was hiding inside the modified leaf of a species of Sarracenia, a carnivorous plant commonly known as a North American pitcher plant. There are at least eight species of Sarracenia, all of which naturally occur in the southeastern region of the United States. One species, Sarracenia purpurea, also occurs in the northeast, the upper Midwest, and throughout much of Canada. Sarracenia is in the family Sarraceniaceae along with two other genera of pitcher plants, Darlingtonia (the cobra plant, native to northern California and southern Oregon) and Heliamphora (the sun pitchers, native to South America). Plants in this family are not to be confused with the distantly related tropical pitcher plants which are in the genus Nepenthes (family Nepentheaceae).

The natural habitats of Sarracenia are sunny, open areas that remain permanently wet, including meadows, savannahs, fens, and swamps. The soils are acidic, nutrient poor, and typically composed of sandy peat commonly derived from sphagnum moss. In the southeast, less than 5% of the original (pre-European settlement) Sarracenia habitat remains, threatening its survival in the wild. Sarracenia oreophila (green pitcher plant) is currently listed as critically endangered on the IUCN Red List.

Flowering occurs in the spring, usually before pitchers form. Individual flowers are formed on tall stalks that rise straight up and then bend at the very top, hanging the flower upside down. Early flowering and tall flower stalks help prevent pollinating insects from being consumed by the plant. In his book The Savage Garden, Peter D’Amato describes the flowers as “showy, brilliant, and very unusual – a wonderful bonus to an already handsome class of foliage plants.” The flowers are either yellow or a shade of red and last about two weeks, after which the petals drop and a seed pod forms. Seeds are released from the fruits in the fall.

Flower of Sarracenia rubra (sweet pitcherplant) - photo credit: www.eol.org

Flower of Sarracenia rubra (sweet pitcher plant) – photo credit: www.eol.org

D’Amato writes that Sarracenia are among the “most ravenous” plants, with each leaf having the potential of trapping “thousands of nasty insects.” In some cases pitchers even flop over, heavy with the weight of bugs inside them. The specifics of capturing and killing insects varies between species of Sarracenia, but in general prey is lured to the opening of the pitcher with a combination of nectar, scent, and color. Upon entering the tube, gravity, waxy surfaces, drugs, and hairs force the captives downward where they are eventually consumed by enzymes and microbes. Digested insects provide the plant with nutrients necessary for growth – nutrients that otherwise are taken up by the roots of plants that occur in more nutrient rich soils.

Sarracenia purpurea (purple pitcher plant) is unique in that its pitchers lack a “hood” or “lid” – a standard feature of other species of Sarracenia that helps keep rain from entering the pitchers. Instead, the pitchers fill with water and insects are killed by drowning. The most brutal killer is probably Sarracenia psittacina (parrot pitcher plant) which has an additional opening inside of its pitcher. The opening is small and difficult to find again once an insect is on the wrong side of it. The inside walls of the pitcher are covered in long, sharp, downward pointing hairs, and the struggling insect is pierced repeatedly by the hairs as it makes its way to the bottom of the tube to be digested.

Hoodless pitchers of Sarracenia purpurea (photo credit: www.eol.org)

Hoodless pitchers of Sarracenia purpurea (photo credit: www.eol.org)

Hooded pitchers of Sarracenia leucophylla (photo credit: www.eol.org)

Hooded pitchers of Sarracenia leucophylla (photo credit: www.eol.org)

According to D’Amato, “the Sarracenia are one of the simplest carnivorous plants to grow, and certainly among the most fun and rewarding.” Learn more about growing North American pitcher plants by consulting D’Amato’s book and/or by visiting the website of the International Carnivorous Plant Society.

Want to learn more about Sarracenia? The Plants are Cool, Too! web series has a great video about them:

Other carnivorous plant posts:

Year of Pollination: The Anatomy of a Bee

A greater appreciation for pollinators can be had by learning to identify them – being able to tell one from another and calling them by name. Anyone can tell a butterfly from a bee, but how about telling a sweat bee from a leafcutter bee? Or one species of sweat bee from another species of sweat bee? That takes more training. This is where knowing the parts of a bee becomes important.

I am new to learning the names of pollinators. I’ve been learning the names of plants for many years now (and I still have a long way to go), but my knowledge of insect identification is largely limited to one entomology course I took in college and the occasional reading about insects in books and magazines. So, this post is just as much for me as it is for anybody else. It also explains why it is brief and basic. It’s for beginners.

This first illustration is found in the book Pollinators of Native Plants by Heather Holm. The book starts with brief overviews of pollination, pollinators, and pollinator conservation, but then spends nearly 200 pages profiling specific plants and describing the particular species of pollinating insects that visit them. The photos of the insects are great and should be very useful in helping to identify pollinators.

bee anatomy_pollinators of native plants book

This next illustration is from the book California Bees and Blooms by Gordon W. Frankie, et al. The title is a bit deceptive because much of what is found in this book is just as applicable to people outside of California as it is to people within. There is some discussion about plants and pollinators specific to California and the western states, but there is also a lot of great information about bees, flowers, and pollination in general, including some great advice on learning to identify bees. The book includes this basic diagram, but it also provides several other more detailed illustrations that help further describe things like mouth parts, wings, and legs.

bee anatomy_california bees and blooms book

As part of their discussion on identifying bees, the authors of California Bees and Blooms offer these encouraging and helpful words to beginners like me: “Even trained taxonomists must examine most bees under a microscope to identify them to species level, but knowing the characteristics to look for can give you a pretty good idea of the major groups and families of bees that are visiting your garden. These include size, color, and features of the head, thorax, wings, and abdomen.”

If you would like to know more about the pollinators found in your region, including their names, life history, and the plants they visit, books like the aforementioned are a good start. Also, find yourself a copy of a field guide for the insects in your area and a good hand lens. Then spend some time outside closely and quietly observing the busy lives of the tiny things around you. I plan to do more of this sort of thing, and I am excited see what I might find. Let me know what you find.

Here are a few online resources for learning more about bee anatomy and bee identification:

Other “Year of Pollination” Posts:

Plants Use Mycorrhizal Fungi to Warn Each Other of Incoming Threats

The March 2015 issue of New Phytologist is a Special Issue focusing on the “ecology and evolution of mycorrhizas.” This is the second of two articles from that issue that I am reviewing. Read the first review here.

Interplant signalling through hyphal networks by David Johnson and Lucy Gilbert

When an individual plant is attacked by an insect or fungal pest, it can warn neighboring plants – prompting them to produce compounds that either repel the pests or attract beneficial organisms that can fight off the pests. There are two main pathways for a plant to send these communications: through the air by way of volatile organic compounds (VOC’s) or through the soil by way of a vast collection of fungal hyphae called mycelium. Plant communication by aerial release of VOC’s has been well documented; communication via mycelium, however, is a fairly recent discovery, and there is much left to learn.

“The length of hyphae in the soil and the ability of mycorrhizal fungi to form multiple points of entry into roots can lead to the formation of a common mycelial network (CMN) that interconnects two or more plants.” These CMN’s are known to play “key roles in facilitating nutrient transport and redistribution.” We now understand that they can also “facilitate defense against insect herbivores and foliar necrotophic fungi by acting as conduits for interplant signaling.” The purpose of this research is to explore the “mechanisms, evolutionary consequences, and circumstances” surrounding the evolution of this process and to “highlight key gaps in our understanding.”

interplant signaling

An illustration of plant communication (aka interplant signaling) by air and by soil form the article in New Phytologist.

If plants are communicating via CMN’s, how are they doing it? The authors propose three potential mechanisms. The first is by signal molecules being transported “in liquid films on the external surface of hyphae via capillary action or microbes.” They determine that this form of communication would be easily disrupted by soil particles and isn’t likely to occur over long distances. The second mechanism is by molecules being transported within hyphae, passing from cell to cell until they reach their destination. The third mechanism involves an electrical signal induced by wounding.

If signal molecules are involved in the process, what molecules are they? There are some molecules already known to be transported by fungal hyphae (lipids, phosphate transporters, and amino acids) and there are also compounds known to be involved in signaling between plants and mycorrhizal fungi. Exploring these further would be a good place to start. We also need to determine if specific insect and fungal pests or certain types of plant damage result in unique signaling compounds.

It has been established that electrical signals can be produced in response to plant damage. These signals are a result of a process known as membrane depolarization. “A key advantage of electrical-induced defense over mobile chemical is the speed of delivery.” Movement of a molecule through cells occurs significantly slower than an electrical charge, which is important if the distance to transport the message is relatively far and the plant needs to respond quickly to an invasion. Various aspects of fungal physiology and activity have been shown to be driven in part by membrane depolarization, so involving it in interplant signaling isn’t too far-fetched.

photo credit: wikimedia commons

photo credit: wikimedia commons

How and why does a system of interplant communication involving mycorrhizal fungi evolve? And what are the costs and benefits to the plants and fungi involved? Determining costs and benefits will depend largely on further establishing the signaling mechanisms. Exploring real world systems will also help us answer these questions. For example, in a stable environment such as a managed grassland where CMNs are well developed, a significant loss of plants to a pest or disease could be devastating for the mycorrhizal community, so “transferring warning signals” would be highly beneficial. Conversely, in an unstable environment where a CMN is less established, assisting in interplant signaling may be less of an imperative. Regarding questions concerning the degree of specialization involved in herbivore-plant-fungal interactions: if a “generic herbivore signal” is sent to a neighboring plant that is not typically affected by the attacking herbivore, the cost to the plant in putting up its defenses and to the fungus in transporting the message is high and unnecessary. So, in an environment where there are many different plant species, species-specific signals may be selected for over time; in areas where there are few plant species, a generic signal would suffice.

As research continues, the mysteries of “defense-related” interplant communication via CMN’s will be revealed. Field studies are particularly important because they can paint a more accurate picture compared to “highly simplified laboratory conditions.” One exciting thing about this type of communication is that it may mean that some plants are communicating with each other across great distances, since “some species of fungi can be vast.” CMNs can also target specific plants, and compared to communication via aerial VOC’s, the signal will not be diluted by the wind.

Since I am in the process of reading Robin Wall Kimmerer’s book, Braiding Sweetgrass, I have decided to include her description of a tree-mycorrhizal fungi relationship:

The trees in a forest are often interconnected by subterranean networks of mycorrhizae, fungal strands that inhabit tree roots. The mycorrhizal symbiosis enables the fungi to forage for mineral nutrients in the soil and deliver them to the tree in exchange for carbohydrates. The mycorrhizae may form fungal bridges between individual trees, so that all the trees in a forest are connected. These fungal networks appear to redistribute the wealth of carbohydrates from tree to tree. A kind of Robin Hood, they take from the rich and give to the poor so that all the trees arrive at the same carbon surplus at the same time. They weave a web of reciprocity, of giving and taking. In this way, the trees all act as one because the fungi have connected them. Through unity, survival. All flourishing is mutual.