Plant of the week #2

Stylidium graminifolium
(grass trigger-plant)

A brief description:
The grass trigger-plant is a spring flowering plant found predominantly in moist to dry eucalypt woodlands throughout south-eastern Australia. Emerging in late winter, leaves are up to mid-shin height, with the flower-spike up to knee height. Flowers vary from hot pink to white with pink streaks (as above), with the inflorescence covered in small black hairs.

Taxonomy:
The grass trigger-plant is one species of about 130 that belongs to the genus Stylidium (Family: Stylidiaceae). Most species are Australian, however there are some found throughout south-east Asia.

Distribution: Eastern states; eastern SA, Vic, Tas, NSW (eastern coast) and QLD (south-east).

Conservation status: Locally common; not considered at risk in the wild

Interesting things about trigger-plants:
The flowers of trigger-plants are insect pollinated, and it is from the flowers that the plant derives both it's common and genus names. The flower consists of 5 petals (4 clearly visible, one tucked back up behind the trigger) and fused stamens (2) and style that form a trigger. This trigger is pulled backwards (like cocking a gun), and when an insect lands on the flower it is released, swinging forward and stamping pollen onto the back of the insect's head. You can see this trigger clearly locked-and-loaded in the photo below. Unfortunately I wasn't smart enough to trigger it and take a before/after photo. Perhaps next time? ;)

Problems with photosynthesis (part 1): Maintaining water balance

As promised, a (slightly late) post about photosynthesis, and some of the problems that plants face when they try to do it. Because these can get complicated, I'll split it into 3 posts. Firstly we'll deal with maintaining water balance, and then photodamage caused by excess light (including the xanthophyll cycle - a really cool bit of evolution involving photosynthetic pigments). The last post will be an introduction to the actual process of photosynthesis at a molecular level, and the development of different kinds of photosynthesis to suit different environments (known as C3, C4 and CAM photosynthesis), and subsequently why higher CO2 levels are not necessarily a useful thing for most plants.

So, as every year 7 student can tell you, plants take up carbon dioxide from the atmosphere, water from the soil and absorb sunlight to magically produce sugars. The process is really a marvel of evolution, and involves complex chain-reactions at a molecular level. However for this to even begin, the basic ingredients (CO2, sunlight and water) need to be collected. Most plants use their leaves to obtain the first two, and roots to gather water (by the mechanisms discussed in the previous post!), although of course there are exceptions to this rule (some plants photosynthesise in only their stems, others are parasitic and get water from their hosts rather than root systems, but you get what I mean).
However one of the biggest problems plants have while trying to photosynthesise is maintaining a balance of all 3 requirements, and particularly maintaining enough water to survive (how well they do this is known as their Water Use Efficiency - WUE).

The means by which plants take-up CO2 is through the pores in their leaves known as stomata (singular: stoma). Plants have direct control over these pores, and can open and close them when they need. Opening stomata to uptake CO2 allows the absorption of carbon necessary for photosynthesis to occur, however it also allows water (and oxygen) to escape the leaf, and the plants have little control over this. Consequently in times of water-stress, plants must close their stomata and cease photosynthesis or they will lose valuable water. However allowing water to evaporate from the leaf in hot weather can also assist in cooling the leaf down, as excess light can heat the leaf and damage the photosynthetic organs within it (the other mechanisms to deal with this problem will be discussed in the next post).

Because this is a big problem, many adaptations to low-water environments have evolved (although usually perennial plants in low-water systems are deep-rooted as well). Three of the most common dry-climate adaptations include:

1. Reduced leaf area: This allows for fewer stomata to lose water per unit leaf area, and consequently a greater WUE, although as it does decrease the rate of absorption of CO2 these plants are usually slower-growing than plants without this adaptation. Often leaves are fleshy and succulent as well, and store fluids even in dry times. In some plants, such as cacti, the leaves are so reduced they became spines, and photosynthesis occurs in the stem, while the spines protect the valuable photosynthetic stem from herbivores.

2. Light colouring/hairs on leaves: Many species have a woolly coating on their leaves, intended to reflect excess light. If a leaf remains cooler, less water will be driven from it through evaporation, and the chances of damaging photosynthetic structures is lower. Saltbush and many other arid species are examples of plants that use this protective mechanism.

3. Sunken/hairy stomata: This is really quite cool - many plants have pits and/or hairs in the leaf surface that create a cooler, more moist microclimate around each stoma, reducing water loss but still allowing CO2 to enter the leaf. Banksia species often show this sort of adaptation, particularly those found in the drier regions of Western Australia.

Other plants have more simple mechanisms to deal with waterloss, such as members of the Eucalyptus genus that have leaves that hang downwards, rather than holding them horizontally. This ensures that during the morning and afternoon when the sunlight is cooler the leaves are exposed to it, but when it is overhead and hot at midday the thin edge of the leaf is the only part exposed. This simple anatomical re-arrangement dramatically reduces water loss and allows the trees to grow easily in hot, dry environments (now go find a gumtree and see what I mean!)

So to sum up, plants (like all living things) need to maintain their internal water levels to survive, but also have to balance collecting the ingredients required for photosynthesise. They have evolved many different ways to achieve this, while maintaining a capacity to collect sunlight for photosynthesis. Stay tuned for the next post on the nifty mechanisms used to deal with excess (hence potentially damaging) sunlight.

A word on water potential

So it's time for the first of the physiology posts.

Water is essential for all life on earth. Without a plentiful supply of it, we certainly wouldn't be here. Plants originated in aquatic environments, and one of the many challenges they had to overcome when they made their move onto dry land was how to obtain water. They cannot actively drink it like we can, so a way to passively move water from their roots to the stems evolved.

In order to regulate the water within their tissues, plants use pressure gradients. Because water will always flow from an area of high pressure to low pressure, by creating a pressure gradient in the tissues of the leaves water will be drawn into them from the stem, and into the stem from the roots. In this way, the whole plant becomes a pressure gradient - the roots always have the highest water potential, followed by the stems and finally the leaves. By opening and closing their stomata (pores on the leaf surface), water can leave the plant, and the gradient can continually function (otherwise the water would build up in the leaves, the pressure would increase and the gradient would eventually stop).
During drought of course the plant conserves it's water by closing the stomata, and usually the water potential of the whole plant decreases. If it continues without water for too long, leaves wilt and the plant eventually dies.

So, the underlying question about all this is how does the plant create different pressures in its tissues? There are two basic ways to achieve this. Firstly, you can change the volume of the plant cell, without altering it's size (think of a bottle of fizzy drink - if you shake it and the gas leaves the drink but you've not opened the bottletop, the bottle becomes highly pressurised), or you can pack the interior of the cell with solutes such as salt, and water will be drawn into it. Typically plants use solute loading to decrease and increase their water potential, taking up salts such as potassium from the soil and ground water.

In a nutshell, plants can use water thanks to basic physics. They can regulate their water use through a variety of mechanisms, all of which are vitally important for the plants photosynthesis and survival. An important component of why plants water regulate the way they do is a need to balance water loss with the uptake of the carbon dioxide necessary for photosynthesis (which occurs when stomata are open). So this will be the subject of the next post :)

Plant of the Week #1

Amyema miquilii
(common box mistletoe)

A brief description:
Common box, or drooping, mistletoe is a hemiparasitic plant. This means it takes water and the associated dissolved nutrients (such as nitrogen) from it's host, through a structure called a haustorium. Mistletoes are stem parasites, and as such depend on their hosts for survival. Because of this, contrary to popular belief, they rarely kill their hosts. The red flowers appear in late summer and throughout autumn, and the fleshy fruits develop soon after flowering. Pollination and fruit dispersal is bird assisted, with the seeds leaving the birds gut encased in a sticky, glue-like substance. The birds then wipe this against a branch (to remove it), and the seed sticks to the branch. If it has been deposited on a suitable host, the seed will quickly germinate, and forms a strong attachment to the host.

Common hosts for this species include members of the Eucalyptus and Acacia genera.

Taxonomy:
The common box mistletoe is one species of about 100 that belongs to the genus Amyema (Family: Loranthaceae). There are about 35 species found throughout Australia.

Distribution:
A. miquilii is present in all mainland states of Australia

Conservation status: Common; widespread (throughout Australia)

Interesting things about mistletoes
Mistletoes are key food sources for birds (both pollinators and fruit eaters), as well as insects such as butterfly larvae. Mistletoes can also be nutrient accumulators. Being hemiparasitic, they are not water limited during droughts, as their hosts provide a reliable water source. Because they can rapidly use water without drying out, the nutrients carried by that water are deposited in the leaves and nutrients can accumulate. Mistletoes have been known to directly affect the distribution of nutrients in the landscape, with their leaves releasing patches of nutrients back into the soil as they decay.

Firstly, to science!

The inspiration for this particular post is two-fold. I'd been intending to write something along these lines for a while, but hadn't so far gotten around to it. Considering Easter has just come and gone, and there was, shall we say an 'enthusiastic', debate on a particular TV show last night it has prompted me to actually do it.
Writing about the scientific process, and science as a 'new religion' I think is a good starting point for this particular blog. So here we go!

First and foremost, science is a process. It is a methodology used to uncover information about the world around us, and to discover how the systems within that world function and interact with one another. It is not about proving things to be true, or about dogma (usually - although in some disciplines it does sneak in with some theories) but instead is about experimentation and discovery of the most plausible explanation available at the time, and the ability to switch to an alternative and better explanation should one ever arise.
In this, is the core of the power of science.
Because of the way science functions, better explanations for phenomena are always sought. Dogma rarely takes hold, and if there is insufficient evidence to support them, theories do not progress very far. Even widely accepted theories, even those strongly supported over such a long period of time as to be called the 'laws' of science, are continually being put to the test. E=MC(squared), Einstein's famous equation used to explain the relationship between mass, energy and the speed of light (in a vacuum at least) is now again under scrutiny, as are the theories of gravity (well, talk to any quantum physicist about that one), evolution by natural selection (microbiologists, geneticists etc) and Netwon's Laws (those quantum physicists again). That is not to say those laws are now seen as 'untrue' and will be scrapped - far from it. The beauty of science is to continually progress such laws, adjusting them accordingly as new knowledge is gained.
Those who state science is the new religion have no understanding of what either 'science' or 'religion' actually mean, nor what they stand for. Equally, those who boldly state that 'science will eventually answer all our questions' also do not understand the scientific process, nor how it functions within our society. These are two reasons I refuse to give science the capital S that many do (aside of course, from when it is at the beginning of the sentence).

Take, for example, a simple experiment. We're growing tomatoes, and want to know if we add fertiliser twice as often, if they'll grow better/produce more fruit (bear with me, I am a botanist and this is the first appearance of plants in this blog!).
The scientifically designed experiment you'd use, would be to have two 'treatments'. One you could give lots of fertiliser to, and the other none (or much less - termed a 'control'). Then, once they have fruited for whatever length of time you choose, count or weigh the produce and compare the two. It might be expected that the one with more plant-food did better, and for the sake of this example let us say that this is indeed the case.
The purpose of science, however, is not to simply find out whether things are 'true' or not, but also to attempt to explain why they are so. In the case of the tomatoes, the first thought you would have would be that they extra nutrients allowed the plants to produce more fruit. However this may not be the actual effect the nutrients had. There could be many other factors that accounted for this extra fruit, and these are known as variables.
Perhaps the pots the tomatoes were planted in were placed in patchy light? If those with the higher nutrient treatment happened to have more light (due to chance) than the others, this, rather than the nutrient levels, may explain their increased fruit set. If they had more light, they'd also have likely been exposed to higher temperatures, as it gets hot in the sun. Or it could be something else - perhaps the extra nutrients allowed them to grow more roots, take up more water and then produce more fruit? Or perhaps it was some other chemical or biological process, such as the particular blend of those extra nutrients allowing a particular beneficial microbe to grow in the soil with the plant, and hence increase the fruit production. Or the presence of the fertiliser may have changed the pH level of the soil, and allowed previously inaccessible nutrient sources to be 'unlocked' for the plant by changing them to a different form. Any one of these explanations could tell us why higher nutrients caused a greater fruit set, and each could have it's own experiment set up to investigate it. Or, better yet, the scientist would have had some ideas as to why nutrients would work before they started, and would have built tests for some of these factors into the original experiment (known as 'controlled' variables).

So from this terrifically simple example, you can see how complicated science can get. Without the question of 'why' as well as 'does', we could easily conclude that the additional fertiliser works because fertiliser is magic, and our knowledge of the system would barely increase at all. The point of this example is to illustrate one of my favourite aspects of science. Think of it, if you will, as the mythical beast, a hydra.
Chop off one head, or answer one question, and another two will appear in it's place.
This is the fundamental reason that science can never answer all our questions. But in the past few centuries, and certainly within the last one, our scientific endeavour has brought us so very far. Our knowledge base is rapidly increasing, and the rate of new advancements in science is also accelerating. Having said all of this, I don't see our hydra situation as a problem. As our knowledge increases, so does our want to learn. Learning is good for us, if we didn't learn we would still be monkeys sitting around in trees in Africa (well, there is another contested theory - the 'out of Africa' theory). And yes, I know monkeys can and do learn but you know what I mean.


In a nutshell, science is a remarkable process by which we learn about the world around us. It is not some god worthy of worship, nor does it attempt to be. It is a tool we use to understand the universe we live in, and hopefully one that will allow us to improve our lives and the lives of those to come.