Botany

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Baobab Trees Facing Extinction

Declining populations of baobab trees have been a concern for more than a decade now. That concern has been amplified with the release of a recent study that shows that two baobab tree species endemic to Madagascar risk losing the majority of their available habitat due to climate change and human development in the coming decades.

Baobab trees are spectacular sights. Unique in appearance, they can grow up to about 100 feet tall with trunk diameters as wide as 36 feet and can live for hundreds (possibly thousands) of years. As the trees age, they develop hollow trunks used for storing water (as much as 26,000 gallons!) to help them survive long periods of drought. The fruits of baobab trees are coconut-sized and edible and are said to taste like sherbet. The leaves of at least one species are eaten as a vegetable, and the seeds of some species are used to make vegetable oil. Various other products, including fibers, dyes, and fuel are also derived from baobab trees.

There are nine species of baobab trees (Adansonia spp.). Eight are native to Africa and one is native to Australia. Two of the African species are also found on the Arabian Peninsula, and six of the African species are found only on Madagascar. Three of the Madagascan species (A. grandidieri, A. perrieri, and A. suarezensis) are listed as endangered on the IUCN Red List. Currently, A. perrieri has the lowest population of the three species, with only 99 observed trees. It is estimated that by 2080, its range will be reduced to 30% of what it currently is, further threatening its survival. A. suarezensis has a considerably larger population (15,000 trees) but a much smaller distribution area (1,200 square kilometers). By 2050, this area is estimated to be reduced to only 17 square kilometers, practically guaranteeing its eventual extinction. On the bright side, A. grandidieri has a population of about one million trees and an extensive range that should remain largely undisturbed in the coming decades.

An interesting component to this story is how giant tortoises fit in. The fruits and seeds of baobab trees are relatively large, and so their dispersal is best carried out by animals. Seeds that fall too close to the parent trees have little chance of survival since they will be shaded out and will have to compete with large, adjacent trees. Animals that eat the fruits of the baobab trees help to disperse the seeds by defecating them in areas away from large trees where the seedlings will have a greater chance of survival. Two species of giant tortoises that were once native to Madagascar but have now been extinct for hundreds of years were likely primary dispersers of baobab tree seeds. A recent study used a species of giant tortoise not native to Madagascar (the Aldabra giant tortoise) to test this hypothesis. The tortoise readily consume the fruit of the baobab tree. The seeds remain in the tortoise’s digestive system for up to 23 days, giving the tortoise plenty of time to move to an area suitable for seed germination. Given these findings, biologists are currently working to introduce Aldabra giant tortoises to Madagascar to help save the baobab trees.

Climate change, loss of habitat due to human development, and loss of seed dispersers due to extinction threaten the survival of some baobab tree species, but by recognizing this threat, biologists can work towards preventing their eventual extinction. As we gain a better understanding and appreciation for the need for biodiversity on our planet, we will resolve to take greater steps to protect it.

To learn more about baobab trees facing extinction and giant tortoises as seed dispersers, visit the Scientific American blog, Extinction Countdown, here and here.

baobab tree

Adansonia grandidieri

photo credit: wikimedia commons

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Documentary: What Plants Talk About

Earlier this summer I posted a review of a book called, What a Plant Knows, by Daniel Chamovitz. It’s a book that describes plant senses – senses that are similar to human senses (i.e. seeing, hearing, smelling, etc.). Plants are much more aware of their surroundings than we might initially think, and so I recommend this book to anyone interested in gaining a better understanding of plants and their “awareness”. However, I also understand that this can be an intimidating subject – especially for those who haven’t spent much time studying plants and their biology. Chamovitz wrote his book with the intention of making this subject accessible to everyone. Anyone with even a limited understanding of biology should be able to understand the basic concepts in Chamovitz’s book. However, the subject can still be challenging.

Luckily, a recent documentary by PBS explores similar concepts. It simplifies things even more – exploring the ways in which plants communicate with the world around them, even without having the organs we typically attribute to communication and awareness (i.e. brains, ears, eyes, etc.). The documentary is called What Plants Talk About. I watched it recently and was reminded of Chamovitz’s book. They fit together so well. If you have any interest in this subject at all, I recommend both. If all you are after is a simple introduction, watch the documentary. If the documentary intrigues you, read the book.

There is a lot more to learn about plants and their “awareness,” but these sources are a great start. Watch the documentary and/or read the book and then let me know what you think in the comments below. Meanwhile, we wait in anticipation of what science might discover next concerning this remarkable aspect of the plant kingdom.

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Autumn Leaves

It’s October, so fall is in full force in the northern hemisphere. Days are shorter and temperatures are cooler, but one sure sign that fall is here is that the leaves on deciduous trees are changing colors. Every autumn, leaves that were once a familiar green turn brilliantly red, fiery orange, or vibrantly yellow. And then they fall to the ground leaving trees exposed – just trunks and branches  – skeletons of what they once were during warmer and brighter days.

But why?

Surprisingly enough, the colors seen in autumn are largely present in the leaves throughout their lives, but we don’t see them. We only see green. This is because chloroplasts (cell organelles responsible for carrying out photosynthesis) contain chlorophyll, one of three main pigments found in the cells of leaves throughout the growing season. Chlorophyll absorbs red and blue light and reflects green light. Because chloroplasts are so abundant in the cells of leaves, leaves look green.

But carotenoids are hanging around, too. The second of the three main pigments, carotenoids protect chlorophyll from oxidation and aid in photosynthesis. They reflect blue-green and blue light and appear yellow, however their population is considerably smaller compared to chlorophyll, so their yellow color is masked.

When day length decreases, the level of chlorophyll in plant cells diminishes. As a result, the yellow color of the carotenoids begins to show. Also, a layer of cells called the abscission layer forms between branches and petioles (i.e. leaf stems). This abscission layer is what eventually causes branches to drop their leaves. As the chlorophyll begins to die off and the abscission layer forms, anthocyanins (the third of the three main pigments found in plant cells) are synthesized. Anthocyanins absorb blue, blue-green, and green light and appear red.

With chlorophyll virtually absent (and photosynthesis brought to a halt) carotenoids and anthocyanins become the major pigments found in leaves, giving them the autumn colors we are accustomed to seeing. But here is where it gets tricky…

Fall leaf color is largely dependent on various environmental conditions, including temperature, amount of sunlight, and soil moisture. If autumn is warm and wet, chlorophyll may be slow to die, and anthocyanins may be slow to form. Chlorophyll drops off more readily when it is cool and dry, and anthocyanins synthesize more readily when days are sunny. Dry, sunny days followed by cool, dry nights are said to offer the most vibrant fall colors. Additionally, global climate change is now playing a role, so fall colors may start to appear earlier or later or last longer or shorter depending on the region.

Do you have a favorite place to view fall foliage? Add your comments below.

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Cornus sericia – red-osier dogwood

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Ribes aureum – golden current

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Quercus palustris – pin oak

ash

Fraxinus sp. – ash

ailanthus

Rhus sp. – sumac

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Wildflower Walk: September 2013

Recently I was on a seed collecting trip at Bannister Basin in Payette County, Idaho. From a distance, the area looks like a barren wasteland – especially this time of year. It is hot, dry, and brown. The rolling hills are mostly bare except for dried up weedy grasses and occasional shrubs, and there isn’t a single tree in sight. However, a short hike through the area reveals some interesting plants and bits of color scattered among the drab landscape. It was obviously not the best time or place for a wildflower walk, but the following pictures show a few of the flowers that I was able to find. These are tough species, flourishing in a harsh environment.

chrysothamnus viscidiflorus

Chrysothamnus viscidiflorus – green rabbitbrush

machaeranthera canescens

Machaeranthera canescens – hoary tansyaster

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Eriogonum strictum – strict buckwheat

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Eriogonum sp. – buckwheat

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Plant vs. Bike

Summer is drawing to a close in the northern hemisphere. Days are getting shorter. Nights are getting cooler. Fall flowers are beginning to bloom. And bicycles are getting more flat tires.

As an avid bicyclist, I am particularly aware of the waning summer season, especially since I live in a region where Tribulus terrestris is a prevalent weed. Commonly known as puncturevine or goathead, this nuisance plant is the bane of many cyclists’ existence. While the plant itself appears innocent, its fruit is quite the opposite. Rough around the edges and bearing large, rigid spines, puncturevine fruits easily penetrate bike tires, causing flats. They can also result in an uncomfortable experience for the bare-footed.

Native to the Mediterranean region, puncturevine made its way to North America sometime during the European immigration and has since spread across the continent. The fruit of puncturevine is called a bur. Plants with this type of fruit are benefited in two main ways: herbivory deterrent and seed dispersal. The spinyness of the burs deters insects and animals from eating their seeds, and the spines of the burs attach to the feet and fur of animals, etc., aiding in the dispersal of their seeds.

In cool climates, puncturevine is a summer annual. It appears in the heat of the summer, and by late summer the plants have mostly died off, leaving behind hordes of burs, awaiting the arrival of unsuspecting animals, bike tires, and otherwise. The spines of the burs attach themselves to these unsuspecting vicitims and are spread far and wide. The plants typically grow prostrate but can grow upright when they are in shade or being crowded out. They produce large mats that can spread as wide as 6 feet. Their leaves are oppositely oriented and are pinnately compound. Their flowers are small with five bright yellow petals that appear singularly in the axils of leaves. Their fruits are burs that split into 4-5 sections, each containing 1-2 large spines. Their seeds can remain viable for up to 20 years. Puncturevine is a fast growing, drought-tolerant plant with a long, slender taproot. It is commonly found in disturbed sites, along roadways and walkways, and in pastures and fields.

While I am fascinated by this plant, I also abhor it, and so I make an effort to remove and kill it whenever possible. If it weren’t for the countless flat tires it has caused me, I’d probably be more willing to let it be. Bike enthusiasts who have experienced this nuisance nod in agreement.

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Tribulus terrestris looking sweet and innocent

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Close-ups of pretty flowers, interesting leaves, and evil burs

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Bur of puncturevine puncturing bike tire

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Interview with Peter D’Amato of The Savage Garden

In my last post about sundews, I referenced a book about carnivorous plants called, The Savage Garden, by Peter D’Amato. Earlier this month, a revised edition of The Savage Garden was released by Ten Speed Press. Recently, D’Amato appeared on Real Dirt, a garden podcast hosted by Ken Druse, to tell his story, promote the revised edition of his book, and talk about carnivorous plant cultivation. It’s a fascinating discussion, and I highly recommend checking it out.

real dirt

Also, check out the website for Peter D’Amato’s carnivorous plant nursery, California Carnivores.

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The Sundews

Earlier this year, I wrote about northern pitcher plants and how they are helping us to better understand food webs. At that time I promised future posts about carnivorous plants, so I have decided to write about sundews, the only carnivorous plant that I currently have in my collection.

Sundews are members of the genus Drosera and are in the family Droseraceae (the same family as the Venus flytrap). With as many as 194 species, Drosera is one of the largest and most diverse genera of carnivorous plants. Sundews can be found in a wide variety of climates and on nearly every continent, from subarctic Alaska to tropical Brazil. They can be as small as a penny or as big as a small shrub. Their leaves form rosettes and come in numerous shapes and sizes, including circular, wedge-shaped, oval,  forked, fern-like, and grass-like. Drosera flowers are also quite diverse, but typically they are flat, five-petaled, white or pink, and appear in clusters at the top of a tall stalk.

As described so far, you may be thinking that sundews sound quite simple and innocent, but this is certainly not the case. Covering the surfaces of Drosera leaves are dozens of hair-like filaments. At the end of each filament (or tentacle) is a gland, which produces a small drop of clear and very sticky dew. Attracted to the glistening dew and mistaking it for plant nectar, insects fly into it and find themselves instantly stuck. Struggling to get away, an insect may tear off body parts as it flails about, only to fall into other nearby dew droplets, worsening its ensnarement and ensuring its fate.

In his book, The Savage Garden, Peter D’Amato describes it this way:

“Sundews are innocent-looking and pretty, their delicate leaves sparkling with the promise of sweet nectar, but the foolish insect curious enough to give a sundew the slightest touch will suddenly find itself caught in a living nightmare. Doomed to a horrible death, the insect may struggle for a blessed few minutes or suffer for untold hours as it tries to break free of ensnaring, suffocating glue, grasping tentacles, and burning acids and enzymes; meanwhile, its precious bodily fluids are being slowly sucked dry.”

As the sticky dew attracts and then traps the insects, and the tentacles that support the dew help to further ensnare them, imminent death comes in a variety of ways. The most common for small insects is suffocation, as the glue almost immediately covers up the breathing holes on their abdomens. Larger insects that manage to avoid bodily contact with the glue will instead dangle from the plant and die of starvation or exhaustion. Those that break free, losing an appendage or appendages in the process, usually don’t last long after that and are often trapped and killed by spiders who build their webs around sundews in order to take advantage of such occasions. The leaves of some sundews curl up around their prey, not necessarily to further ensnare them, but to surround them with the largest possible number of glands which will help quicken the consumption and digestion process. By now you can see that as innocent and delicate as they may appear, sundews are in fact about as brutal and unforgiving as they come.

If you’d like to learn more about sundews and other carnivorous plants, including information on how to grow them, I highly recommend D’Amato’s book (The Savage Garden). It’s a fascinating and informative read, and the reality of the natural world described therein will astound you.

Drosera chrysolepis

Drosera chrysolepis, photo credit: wikimedia commons

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Book Review: What a Plant Knows

What a Plant Knows: A Field Guide to the Senses
by Daniel Chamovitz

Humans commonly anthropomorphize non-humans. It just seems easier, for example, to say that a plant “likes” a particular type of soil, even though we know that a plant doesn’t “like” anything because a plant does not experience emotion. What we really mean to say is that a plant is adapted to and therefore performs best in a particular type of soil. However, knowing this, is it plausible at all to say that a plant can see, smell, feel, hear, sense its location, or remember things? Daniel Chamovitz argues that it is, and he has plenty of credible research to support his thesis.

In short, plants have senses very similar to human senses and are far more aware than we might initially think. To be clear though, Chamovitz states early on in his book that his “use of the word ‘know’ is unorthodox. Plants don’t have a central nervous system; a plant doesn’t have a brain that coordinates information for its entire body.” Nor do they have noses or ears or eyes. Instead, when Chamovitz uses words like “see,” “smell,” “hear,” and “know,” he is referring to various chemical reactions and physiological phenomena that occur in plants which produce reactions that are analogous to human senses. When a willow tree is damaged by tent caterpillars, a neighboring willow tree becomes unpalatable to the caterpillars and thereby resists a similar fate. Why? Because the damaged willow tree releases a gaseous substance that nearby willow trees can sense (or “smell”). This is a signal for them to protect themselves by building up toxic chemicals in their leaves.

Another example offered by Chamovitz involves the ability of some plants to remember winter. Cherry blossoms appear in the spring because winter has passed. A certain period of cold temperatures is what induces this response. If the trees bloom too early, the blossoms will freeze. If they bloom too late, the fruits would not have time to mature before cold temperatures returned. The seeds of winter wheat are planted in the fall and germinate in the spring. They also require a period of cold temperatures in order to germinate. This process is called vernalization, and it involves a specific gene in the plant called flowering locus C (FLC). After vernalization, this gene is turned off which signals the plant to flower (provided that other environmental conditions, such as light and soil temperature, are conducive to flowering, etc.).

A common myth is that plants grow better when people say nice things to them or play relaxing music for them. Chamovitz thoroughly debunks this myth and concludes that no evidence has been found for plants being able to hear. Plants do however possess many of the same genes that humans possess, including several genes that when not functioning properly can result in deafness in humans. These genes encode proteins called myosins. Myosins in humans help form the hair cells in our inner ears which are essential for hearing. Myosins in plants help form root hairs which are essential for absorbing water from the soil. While the functions of these proteins are quite different in humans and plants, mutations in the genes code for these proteins can have drastic results for both.

All this talk about chemistry, genetics, and physiology may sound a bit intimidating…but don’t worry. While Chamovitz endeavours to tell the science accurately and in detail, he does so in a very approachable manner, making this an easy read for anyone with a basic understanding of biology. Even if you don’t fully comprehend the technical stuff, the anecdotes are well told and captivating, and after you finish reading this, you are certain to have a greater appreciation for plants and all of the fascinating things that they can do. While we should be careful to be too anthropocentric, this book makes it clear that plants are a lot like us…or should I say, we are a lot like plants? Either way, we have many things in common (including much of our DNA), which is all the more reason to appreciate plants for the amazing organisms that they are.

This is a video (recommended by Chamovitz) of a dodder plant sensing the location of a tomato plant. Dodder is unable to photosynthesize, so after attaching itself to the tomato plant it will feed on the nutrients that the tomato plant produces.

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– Excerpt from What a Plant Knows

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American Penstemon Society Field Trip

This past weekend, the American Penstemon Society held their annual meeting in Boise, Idaho. I was fortunate enough to attend their meeting and join them on one of their field trips. We visited Mores Mountain in the Boise National Forest, which is a short drive north of Boise. The hike was so much fun! There were tons of great plants to see, and the views from the top were incredible. My favorite sights were all the magical rock gardens that were scattered along the trail which were loaded with a diverse number of small plants eking out an existence on lichen splattered outcrops. If you ever find yourself in the Boise area, this is a spot that I am certain you don’t want to miss.

rock garden

Rock Garden on Mores Mountain, Boise National Forest

lewisia sacajaweana

Lewisia sacajaweana, Sacajawea bitter root

ceanothus velutinus

Ceanothus velutinus, snowbrush ceanothus

penstemon humilis

Penstemon humilis, low penstemon

penstemon fruticosus

Penstemon fruticosus, shrubby penstemon

calochortus macrocarpus

Calochortus macrocarpus, sagebrush mariposa lily

calochortus eurycarpus

Calochortus eurycarpus, white mariposa lily

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Wildflower Walk: June 2013

Camping recently with family and friends affored me the opportunity to explore some early summer wildflowers near Grimes Creek in the Boise National Forest. Despite the noise and dust presented by regular ATV and dirt bike traffic, I had a very enjoyable weekend in the woods. What follows are some of the wildflowers I saw while exploring the area.

erigeron pumilus

Erigeron pumilus, shaggy fleabane

geranium viscosissimum

Geranium viscosissimum, sticky purple geranium

ipomopsis aggregata

Ipomopsis aggregata, scarlet gilia

penstemon deustus

Penstemon deustus, hotrock or scabland penstemon

penstemon payettensis

Penstemon payettensis, Payette penstemon