Tag Archives: plants

Innovative plant: How does the dandelion drift its seeds?

How far do you think a dandelion seed can drift from its base plant?

The Common Dandelion (Taraxacum officinale) primarily relies on wind flow to scatter its seeds. The dandelion seed has a fluffy structure that enables it to hold the most prolonged wind-based dispersal record. Commonly the seeds land 2 meters away from their mother plant. Still, in windy, dry weather favored by the dandelion, the seeds can fly up to 30 kilometers and even far (150 kilometers in some conditions). The vital point in this extraordinary adventure of the dandelion is flying with a constant velocity and having a short descent time, which means it should stay stable in the air for a relatively long time.

A study tried to illuminate the mystery behind the dandelion seeds’ ability to stay aloft in the air. Researchers attempted to mimic the dandelion flight using similarly structured silicon disks in a wind tunnel that simulated the airflow around the pappus. Pappus, the flying seed of the dandelion, consists of radially oriented filaments, each interacting with other adjacent ones, resulting in a reduction in the airflow. They compared the flight of natural seeds collected from one plant with several silicon disks with different porosities.

Dandelion seeds and silicon disks in wind tunnel
Wind tunnel experiment, modified from Cathal Cummins & et al. 2018
vortex ring above pappus
Pappus & separated vortex ring, modified from Madeleine Seale & et al. 2019

Their results showed that when pappus separates into the air,  it forms an air bubble detached from its surface above it. This air bubble, known as a vortex, is unique to the dandelion seed. When the pappus is released in the air, it takes some time to reach a steady point, in which the vortex becomes symmetrical. An important feature affecting this symmetry is the porosity of the pappus, defined by the number of filaments and their dimension in each pappus— generally, the more the porosity, the steadier the flight. The best porosity for a stable vortex ring is greater than 84.97%, and the vortex ring begins to separate as the porosity falls below 77.42%. The experiment also indicated that the vortex is axisymmetric in low velocities, but it begins to lose its symmetry as the Reynolds increases.

Pappus with water drops on it
Pappus in moisture, photo by enfantnocta

This phenomenal plant has evolved techniques for mass germination, even in the absence of wind! Pappus’s hairy structure enables it to attach to an animal’s skin and soil particles, assuring the dandelion to have enough seed dispersion during the flowering season. More interestingly, the dandelion is known to have an informed dispersal in response to environmental fluctuations. When the plant experiences root herbivory, it intensifies the seed dispersal. The flight distance may vary from meters to kilometers to assure good germination in the absence of threatening conditions. Imagine a rainy day; the moist weather condition makes the pappus’ bristles come close together, reducing the possibility of separating from the plant. The moisture makes the current spot a suitable choice to stay. So even the detached seeds prefer to fall close to their base plant. 

It worth mentioning that this remarkable plant also inspired areas of science. In their study of Mars exploration, researchers presented a primary model of a dandelion-inspired rover. Considering the harsh environmental condition on Mars, other excavators find the wind flow as an obstacle that results in damaged parts and incomplete missions. In contrast, the new dandelion-shaped rovers use the wind flow as an accelerating point to explore locations on Mars that other robots couldn’t access.

Dandelion-shaped Mars rovers
Dandelion-shaped rovers ,modified from Michelle Sherman & et al. 2020

sticks and stones may break my bones but dirt will wash right off

There you are, sitting in the park eating your spaghetti picnic on your favorite picnic blanket when your pollen allergy acts up. You let out a sneeze powerful enough to compete with Aeolus’ bag of wind, but now your spaghetti is all over your favorite picnic blanket. You immediately go to rinse it off, but your fine Italian sauce has thoroughly soaked in. If only nature had a solution to keep a surface clean. Enter: the lotus leaf.

The lotus leaf is renowned for its ability to stay clean in murky environments. This characteristic of the plant is regularly attributed to its superhydrophobic surface features and chemistry. A superhydrophobic surface is a surface which can maintain a contact angle with water above 150o and is correlated with a low free surface energy—which really means water pools and rolls off rather than soaking into the surface.

Nearly perfectly spherical water droplet on an artificially prepared surface

Modified from Zorba et al. 2008

A key attribute of the superhydrophobic surface is a hierarchical micro- and nanostructure. The microstructure is composed of plant cells grown in little mounds known as a “papillae” with small channels for air flow in between called “stomata.” The nanostructure is composed of hair-like wax crystal towers (epicuticular wax) built on the peaks of the papillae topography. The elevated wax towers combined with the stomata trap air and reduce the contact area of the water with the surface. The epicuticular wax chemistry reduces the adhesion to the towers themselves by being naturally hydrophobic.

Graphic of water drop resting across uneven wax pillars on a lotus leaf

Modified from Zorba et al. 2008

The tips of the wax towers create the largest repelling forces which form larger contact angles, while shorter towers can actually produce adhesive forces that reduce the contact angle. If the air is displaced and filled with water, the contact angle will decrease due to the water-water adhesion which “pulls” the droplet to the surface. Similarly, if the surface is damaged, the wax can be removed and decrease the surface’s hydrophobicity. The wax is naturally soft material and prone to mechanical damage increasing water adhesion and reducing the self-cleaning abilities of the leaf.

The papillae topography is the key to the robustness of the lotus leaf hydrophobicity. The papillae create natural valleys and creases which—like the tops—are still densely packed with wax hairs. When the surface is impacted, only the top of the papillae are exposed to the mechanical force so the wax tubules in the valleys are left undeformed and maintain their hydrophobic characteristics.

Water beads on rain jacket

Photo by Chase Pellerin via Gear Patrol

Hydrophobic surfaces have many applications in everyday life, for example rain jackets and umbrellas perform their best when they are hydrophobic. Manufacturing processes rely on hydrophobic surfaces to reduce oxidation and stay clean in past-paced environments, and your favorite picnic blanket would be much less prone to spaghetti stains if it were hydrophobic. Nature has solutions to keeping surfaces clean; we just have to recognize them.

What Makes and Breaks the World’s Tallest Trees

Trees have the potential to be the largest organisms on Earth. The world’s tallest tree, dubbed Hyperion, is 380 ft tall and weighs over 1,600,000 lbs. Compared this to the world’s largest animal, a particularly massive blue whale which was 100 ft long and weighed 380,000 lbs, the simply massive size of this tree should be obvious. And unlike a whale, a tree is much less likely collapse and crush itself under its own weight. Trees need to be tall, even if doing so consumes a lot of resources, in order to compete for sunlight. So what lets trees get this big, and what limits their height?

A diagram showing a space shuttle, which when prepared to launch is less than half the height of Hyperion, General Sherman, a wider but slightly shorter tree of a different family sequoia, a blue whale that is much shorter than either tree, and the statue of liberty, whose torch barely comes close to the shorter of the two trees
Comparison diagram of the World’s largest trees – Sequoia Tree Comparison Chart, Sequoias

There are two primary rules that govern tree sizes. The first is mechanics, the way the trunk of the tree is built and how it responds to weight. The wood of the biggest trees has a very high strength to weight ratio, which enables a tree to carry its own massive weight without collapsing. The layout and structure of this wood is analyzed at length in the journal by M. Ramage, but in summary, tall trees have internal cells called tracheids. These tiny circular tubes are 2-4 mm long and around 30 μm wide and provide support to the tree and allow water to flow throughout it, without adding as much weight. 

an image showing the tracheid cell structure of wood, many small cylinders stacked on top of each other.
A section of the annual ring of a conifer- M. Ramage’s The wood from the trees: The use of timber in construction and Dr. Krzysztof Wicher.

The high strength to weight ratio of wood allows trees to support themselves at incredible heights. Using B. Blonder’s research about the scaling of trees, it can be shown that trees are so strong and yet comparatively light weight that a tree would not actually collapse under its own weight until it was almost 15 Empire State Buildings tall. Obviously no tree is this tall, meaning some other factors must limit their height, but the incredible strength of wood should now be clear!

A diagram showing the decreasing size of pine needle branch segments. They decrease dramatically as height increases.
Leaf samples taken from the same type of tree with the height they were taken from listed adjacently in meters, – G. Koch’s The limits of tree height

The second primary rule that governs tree size is hydraulics, and it restricts the height a tree can reach. Hydraulics defines a tree’s ability to move water from its roots to its upper leaves in order to perform photosynthesis. The taller a tree gets, the more difficult this process becomes until the tree becomes incapable of growing any taller. G. Koch’s article, The Limits to Tree Height, explores how this hydraulic system works and how it restricts the heights a tree can reach. Xylem, tiny internal pipes that run from the roots to the tops of the tree, and carry water in a long continuous column this whole length. The longer this column becomes, the more difficult it is to maintain and the greater suction pressure that occurs at the highest leaves. Koch studied how properties in leaves changed the higher up they could be found, determining that the efficiency of Photosynthesis decreased, the pressure at the end of the xylem increased, and the size of leaves decreased. At great heights, the status of leaves seemed remarkably similar to those of a tree undergoing a severe drought.


Koch determined that these changes with height would eventually hit a maximum limit which they could not exceed, a limit that was determined to occur between 122-130 meters. So while the efficient properties of wood allow trees to reach incredible heights, their restricted ability to move water limits just how tall they can grow.

Sources and Further Reading:

  • Ramage M., Burridge H., Busse-Wicher M., et al. The wood from trees: The use of timber in construction. Renewable and Sustainable Energy Reviews 68, 333-359 (2017)
  • Blonder B. The size of trees: exploring biological scaling (2010)
  • Koch, G., Sillett, S., Jennings, G. et al. The limits to tree height. Nature 428, 851–854 (2004)

Can Plants Talk to Each Other?

When something bad happens, do you tell your friends? Do you warn the people around you?

Similar to human beings telling one another about risks and dangers, plants can communicate with one another about environmental stressors. One stressor for plants is physical contact with other plants, such as their leaves touching. The presence of other plants means competition for resources and the possibility of invasive species. Biologists at the Swedish University of Agricultural Sciences conducted a study on the ability of plants to communicate with neighboring plants through chemical signals excreted through their roots to indicate to neighboring plants that they contacted another plant above ground.

A diagram of a root in a tube with two tubes branching off of it in the shape of an upside-down 'y'. Each branching tube leads to one of the two solutions.
Diagram from Elhakeem et al., PLoS ONE 2018

In their experiment, the Root Choice Test, maize plants were placed in individual chambers where the roots had two possible paths for further growth. One path led to a solution made from the soil of a plant whose leaves had been touched by the leaves of another plant every day for a week. The other solution had soil from a plant that had not been disturbed.

Despite there being an equal chance of growth in either direction, the maize plants chose to grow in the solution of the untouched plant significantly more often. In some cases, a plant would begin to grow roots in the direction of the touched plant’s soil, but then changed growth direction to the other solution. There were no scenarios wherein a plant would switch from the undisturbed plant solution to the touched plant solution.

These results demonstrate a robust system of communication between plants. Plants possess the ability to recognize when their leaves touch another plant’s leaves and can transform this information into a chemical signal released by their roots. Other plants can understand these signals and modify their behavior as a result.

Mushrooms in grass huddled together
Photo by Vince 6800 on Unsplash

Plants can also communicate through physical connection including underground fungal networks. These networks are made up of fungal root hairs called hyphae that insert themselves into the cell membrane of a plant’s roots. Hyphae are made up of long, individual, filamentous branches whose structural characteristics, such as cell wall thickness and branching, are determined by its function. These vast systems of interconnected fungi plants act like telephone wires for communication.

Plants in these networks are able to exchange nutrients, become more resistant to disease, and grow larger. Healthy areas of the fungal network have also been shown to respond defensively when other areas of the network have been under bacterial attack. This shows that the fungal networks and the plants they connect exchange warnings similar to plants communicating though chemical signals in the soil.

Research into plant communication could one day lead to producing desired changes in plants by artificially mimicking their communication. Farmers could create chemical or physical signals that instruct their crops to grow more effectively. As research into this topic continues, perhaps one day, plant communication will be as well understood as any spoken language.

To learn more about plant communication check out these stories: The Scientist, NCBI and PLoS.