Flower anatomy

So I'm going to chicken out here, and only cover floral anatomy. Mostly because I'm a little tired and pressed for time at the moment. Will put up the mechanics of fertilisation in the next post probably.

Basically a flower is there to ensure pollination, so a fertilised seed can be produced.
There are many types of floral anatomy, and it's too complicated to go through them all, however most plants conform to a single type, and have basic variations on that theme.

I'll run through flowers that have both the male and female parts, although as mentioned in the last post, not all flowers do.

Right. Diagram time (wooo paint, because I don't have photoshop on this computer!):

(not bad for a paint job, hey?!)
The parts of the flower and their function are outlined below:

Petal: Can be bright and colourful to attract pollinators. Can vary in size, shape and colour depending on what the plant is trying to attract, if anything at all. Usually in plants that are not trying to attract anything, they're reduced in size and dull in colour, if they're even present at all.

Sepal: (The green bits at the bottom of the Petals) Together they make up the 'Calyx', functionally they may be there purely to protect the flower (while in bud), or they may be specialised and look like petals. For example most orchids have a specialised Calyx that looks like petals. Dasies are another example - the center of the daisy is actually hundreds of tiny flowers, while the 'petals' are actually a specialised Calyx.

Receptacle: Is basically the base of the flower, it is the part where most of the other components are anchored.

Peduncle: The stem of the flower, from the base of the Receptacle right down until it attaches to the branch it's growing on.

 Now the reproductive bits:

Female parts:
Stigma: The part that catches pollen for fertilisation, and part of the Pistil of the flower. Usually it's sticky and pollen-catching only when receptive to fertilisation. Because of this, if the plant splits up when the male and female parts of the flower are mature, the plant can often avoid many of the problems of self-fertilisation.

Style: The stem the Stigma sits on. This can be long or quite short, together with Stigma and Ovary comprises part two of the Pistil.

Ovary: Found at the base of the style, the Ovary contains the female reproductive parts of the plant, the Ovules. The whole structure from Stigma to Ovary makes up the Pistil. The structure of the Ovary can be quite important for identifying plants; it can have one to many chambers, it can sit above the place where the Petals/Sepals/Stames attach to the Receptacle (superior Ovary), halfway down where they attach (semi-inferior) or below where they attach to the Receptacle (inferior Ovary - perhaps I'll put diagrams up sometime to make that clearer!)

Ovules: Again, there may be one or many hundreds of thousands of these, each having the potential to become a new seed. Not all will be successfully fertilised, think of a pea pod. Sometimes you get those tiny little not-developed peas in there? They're probably aborted seeds, or those Ovules that simply haven't managed to be fertilised.

Male parts:
Anther: The pollen-containing part of the flower. Usually the Anther will split open on maturity, releasing the pollen to allow it to be either carried away by the environment or an animal. What axis the Anther splits open on, or if the pollen just moves through pores etc, is often family or genus specific and can be taxonomically useful.

Filament: The stem that the Anther is found on. Together they make up the Stamen, and this can vary in size, number, shape and position in the flower. Plants that want to avoid fertilising themselves might have the Anthers below the Stigma, to stop pollen from the same flower getting to the Stigma. Or they might have Anthers that sit above the Stigma, but mature either before or after the Stigma becomes receptive to pollen.


So that is basic flower anatomy. Pollen is released by Anthers, aiming to get stuck on Stigmas. But you may have noticed that the Stigma is a long way from the Ovules in the Ovary? How does the pollen get from being stuck on top of the Stigma to fertilise the Ovule in the Ovary? I'll tell you in the next post ;)

Seed plant reproduction

So post #2 in the series about plant reproduction is here!

So in the previous post, alternation of generations was (sort of) explained.
Here we're mostly talking about the sporophyte, which is the tree you see when you walk outside, and how it manages to produce gametophytes, where these occur and how the whole thing works. Starting with seed plants, and touching on flowering plants slightly (although there will be more of those in the next post).

So imagine a pine tree. You know in spring when all the ponds and creeks get covered in yellow grime? Yep, that's pollen. Seed plants like pines are wind-pollinated, resulting in a whole lot of pollen moving around the landscape. But then, that's a price you pay with wind-pollination. It tends to me more hit-and-miss than animal pollination, so more pollen is usually produced to compensate (more on this in a later post, promise!).
The pollen is produced in the male cones, known as microsporangium, and is the entire microgametophyte phase of this plant. Remembering from the last post, where mosses and ferns may have almost a 50/50 split or at least a far more prevalent gametophyte stage, in seed and flowering plants the gametophyte is much smaller, only hangs around for a very short length of time, and is less obvious. The male cones are usually found on the outside of the tree, at the ends of the branches, and this allows for more easy pollen dispersal on the wind.

The female part of the lifecycle occurs completely within the female cone, which is the megasporangium. Under the scales of the cone, there are megagametophytes. These, along with other associated tissues, make up the ova (egg). Once pollen lands on the right part of the girl cone, fertilisation may occur. In this instance, the male pollen (microgametophyte) will fuse with the femle egg (megagametophyte) to form a new embryo (zygote, and it is the next sporophyte phase). This develops as a seed, and once it reaches maturity, can (ideally) be dispersed. So really, 3/4 of the process happens in the female cone (megasporangium) as once the pollen has been developed and dispersed, the microsporangium has little to do with it ;)

So in summary:
- Male cone (microsporangium): Produces pollen (microgametophyte), disperses via wind
- Female cone (megasporangium): Produces the egg (containing megagametophyte), is where fertilisation takes place and where the seed (new sporophyte) develops, protected, until dispersal can occur.

Edit: A picture! To hopefully make that clearer (apologies for bad quality and my terrible handwriting. Haploid stage in yellow, diploid is blue):

Flowering plants work in a very similar way, with only a couple of differences. Firstly, they still split the micro- and mega-gametophytes up, however now they have flowers too. In most flowers you can find both the male and female structures, however some plants have separate flowers for them. Also, some plants are either male or female too. In flowers with both male and female parts, sometimes the same plant can't fertilise itself, sometimes it can. Sometimes the male part sits above the female, sometimes it's the other way around. But the basic mechanics are the same: male pollen, produced in a microsporangium (in the flowers case it's called an anther) meets the female egg, produced in a megasporangium (in the flower it's the ovary), they fuse to form a zygote, which grows into an embryo and develops inside a seed.

The actual mechanics of fertilisation in flowering plants are interesting, but can be a bit complicated. I might do a post regarding basic flower anatomy, and also detail how fertilisation occurs. Then the long-anticipated post about pollination syndromes will come...

Time to give this blog a reboot I think. So a post about the alternation of generations in plants

So my posting went from semi-regular to irregular to nonexistent. Apologies.

So in order to give it a kick in the pants, I think I'll write about... pollination. Or perhaps first the different types of reproductive methods found in the plant kindgom, then end with a post regarding pollination. It's a little complicated, so might take a couple of posts, but at least I haven't covered that yet! I might actually start with the confusing part, which is a process known as alternation of generations, because understanding that will make understanding plant reproduction a whole lot easier.

So, there are several kinds of plants, which are generally thought of at differing evolutionary levels.
Going from the most 'primitive' to the most 'modern' you have the Non-Vascular plants, such as mosses (Bryophytes), the Seedless Vascular plants, such as ferns (Pterophytes), then there are the higher plants which are made up of Seed plants such as connifers (Gymosperms) and finally the Flowering plants (Angiosperms).

Each group of plants has evolved its own way of solving the problem of reproduction, with each level seemingly involving more and more complex structures in order to do so. But first I'll talk about alternation of generations, otherwise known as the alternation of phases or metagenesis. But I know it as alternation of generations ;)

So what does that even mean?
Well, in short it refers to which tissue type (or rather, what that tissue is derived from) makes up which part of a plant's lifecycle, and whether or not this can be easily separated into two separate generations. It was 'discovered' (read: described) by Wilhelm Hofmeister in the late 1800s, and shows clearly why the reproductive structures we see today are necessary for the funtion of the various reproductive methods.

Edit: First a couple of definitions to help out:
Haploid: Cells that contain a single set of chromosomes (n).
Diploid: Cells that contain two sets of the same chromosomes (2n), ie paired chromosomes
Meiosis: The division of a cell whereby the chromosomes do not replicate, resulting in one of each pair of chromosomes occuring in each of the new daughter cells (ie produces 2 haploid (n) cells)
Meitosis: The division of a cell whereby the chromosomes do replicate, and each daughter cell has a pair of each chromosome (ie produces 2 diploid (2n) cells).

There are two basic phases that plant tissues go through. The first is the Sporophyte phase, which is diploid (like us it has 2n chromosomes) and the second is the Gametophyte, which is haploid (has only n chromosomes). Depending on the organism, one phase is usually dependent on the other for surivival, however ins some plants (eg Ferns) the two stages may be capeable of living independently. Following so far? Good :)
The Sporophyte, perhaps unsurprisingly, produces spores, whereas the Gametophyte (also unsurprisingly) produces gametes.

So how does this happen? Well:

The easiest place to start with this is the Sporophyte.
Like I mentioned before, the Sporophyte is diploid (2n), and in most plants it forms the largest and most long-lived part of the lifecycle (for example every part of a tree you can see is the Sporophyte). In Bryophytes (mosses), it's the other way around, and the Gametophyte is dominant, with the Sporophyte only appearing in time to reproduce. In either case the reproduction is what we're interested in here. So selected cells in the Sporophyte undergoes meiosis, and split into 2 haploid (n) cells. Meiosis differs from meitosis in that there is no replication of the DNA within the cell, rather the chromosomes halve in number when the cell divides. So this process produces spores that are haploid, and that will form the basis for the next stage of the life cycle.

The spores then either disperse or don't (depends on the plant) and develop into a haploid Gametophyte stage. In Bryophytes they usually do disperse, and once they have done they grow into the new Gametophyte. The Gametophyte produces gametes through mitosis (remember, the Gametophyte is haploid so must undergo mitosis or the number of chromosomes would be halved again, which would be disasterous!) and depending on the the structure they're produced in, and the plant we're talking about, these are usually different sizes. The male is generally termed the 'microgametophyte' and is a motile sperm (ie it can swim towards the egg), and the female the 'megagametophyte' and is usually a sessile egg (ie it stays still).
Again, depending on the plants we're talking about, these can be produced in specialised structures (in mosses for example the male structure is the antheridium and the female is the archegonium). If fertilisation occurs, the mirco- and megagametophytes fuse and form a new diploid (2n) zygote, which will grow into the new Sporophyte generation and the whole cycle can continue again.

Edit: A picture to help out (because I finally drew one). Using Mosses (Bryophytes) as an example

 

Phew. So that in a nutshell is a brief (and I hope not too confusing) explaination of the alternation of generations in plants. I think that's probably enough to absorb right now, so I might explain how seed plants and flowering plants all fiddle with this in the next few posts ;) Also if I'm really motivated, I might even do some diagrams to try to help explain this a little better (edit: yay! Did that!).

Also if there is a topic you would really like to discuss, leave me a comment and I'll see what I can do about that. I promise nothing (hell, I'm not an expert in any particular field anyway!) but it never hurts to ask :)

I haven't put anything up for a while, so...

Now for something a little different.

If no-one really gets why I feel that ecological studies are so important, and why I do what I do, this video clearly demonstrates why (for more background look for video 01 in the series)

This is a time-lapse of still photography taken at Koonamore Vegetation Reserve in South Australia's North-East Pastoral District. It is a project run and managed by University of Adelaide researchers, and has been ongoing since 1926.
Every year, a field trip heads up there to re-assess the original quadrats established at particular sites, to record the vegetation present. Each year the same fixed quadrats and photopoints are recorded, meaning if you've got a small tree on the left and a large one on the right, it's two photos of the same tree taken at different points in time. This allows a year-by-year insight into the vegetation changes at the station, and it's recovery from a badly over-grazed state. The original photos (taken in the 20s and 30s) can be seen on the left (or top), some of the more recent ones on the right (or bottom).
The changes are astounding.
Livestock and rabbits had completely denuded the soils in the early photos, but now the understory is coming back strongly.

How did they get this to happen? Simple. Fencing the former sheep station to exclude livestock, and beginning rabbit control programs. Larger native grazers, such as kangaroos, can still enter and exit the reserve, but livestock are excluded. Unfortunately rabbits are still present, but are now in much lower nubers than they used to be (rabbit population is indicated on individual photos by the rabbit symbol in the bottom right corner).
This project is unique and very valuable for understanding vegetation shifts in arid Australia. It is the longest running monitoring program of it's type in Australia (by quite a long way) and one of the oldest and longest-running in the world.
If there was ever a way of showing people we really can make a difference by taking some simple and relatively inexpensive steps (eg fencing and careful stock management), then this is it.

Enjoy!

https://www.youtube.com/watch?v=ACU9KCWEV6g&feature=player_embedded

Talking trees

So the long-awaited post on talking trees.

So how on earth does a tree 'talk'?
Plants have multiple ways of communicating, and the way they do it depends on what they're trying to communicate with.
For example, a flower that is long and red and tubular is a signal to birds that there is a tasty sugary treat awaiting them, similarly a rich-smelling fruit would indicate it's ripe and ready to be picked (or from the plant's point of view, dispersed), or a red one might indicate poison.
These are all fairly obvious forms of communication - we can see the flower and smell the fruit. But this isn't what is meant by a plant 'talking'. Besides, this is all communication with animals - what if the plant wanted to communicate with another plant?
There are actually a couple of ways this happens, one through the soil and the other through the air.

Many plants exude compounds from the roots in order for inaccessible nutrients in the soil to be altered to a form the plant can then use. These root 'signals' can be used by more scrupulous species as a way to block the root growth of other plants, or by parasitic plants to find their host.
But this isn't what we mean by trees 'talking' either.

Communication through the air, and hence the leaves, is known as the 'talking tree' effect. According to our anatomy 101, plants have pores called stomata on their leaves which allow the passage of oxygen and water into and out of the leaf. These molecules are able to move in the air, which as any school kid can tell you, is made up of other stuff too. This means any compounds small enough and light enough to move through the air can also enter the leaf, and can then be sensed by the recieving plant. So by releasing certain chemical signals into the air when they're attacked by herbivores, the plant being eaten can then warn other plants in the area that there is a threat around, and those surrounding plants can act accordingly.

Act accordingly?
What can a plant do about it?
Well they can't move, but they can act. Many plants synthesise toxins to discourage herbivores, but do so only when they're under attack. Because of this, most will still lose some leaf tissue before the synthesis of those toxins kicks in as they need to sense the threat first. So if they have the ability to sense other plants are under attack, they can pre-prepare themselves ready for attack, and minimise the damage done to them. Clever!

So what would be the point of this? Why would a plant bother to try to tell another plant there are herbivores in the area? Why not just make your leaves poisonous the whole time? The answers to this is: conserve your resources until they're needed. It uses resources to make toxins, as well as requiring some means of storing them, so why make them unless you need to? Many of these anti-herbivore compounds break down relatively quickly as well, so long-term storage wouldn't be a very good option. By listening in on other plants in the area, toxins can be synthesised only when they're needed, solving the resource and storage problems whilst still protecting the plant.

Cool, eh?

Taxonomy basics (part 3): Drawing a phylogentic tree

As promised, a little methodology on drawing phylogenetic trees. The process is relatively simple to understand - different organisms are grouped according to characters they share. These characters are chosen by the person doing the study, and do need to be defined reasonably carefully. I think a worked example will be best to explain here, so I'm going to go out on a limb and use one from one of my undergrad assignments. The assignment was to draw (by hand) a phylogenetic tree of anything we liked, but it needed to be things, not organisms. I used chocolate bars, and will do so again as it's really good to see how simple characters can group things together.

Basically you need a few simple things to draw a tree. The first are organisms you're studying, and from these you need to derive your characters and their 'states'. To do this, examine the 'organisms' and pick apart their appearance, internal anatomy etc, and these become your characters. You need to be able to give these characters 'states', but these need to be well defined (ie if something is blue and something else red, the character would be colour and the states would be blue and red). For example a character of size might be useful, but if you define the states as 'small, medium or large' then it's an arbitrary measurement and will be impossible for anyone else to use your characters to see how you came up with the tree you did. A better character state would be 0-1.9cm long, 2-3.9cm long, greater than 4cm long (depending of course on what organisms you're describing) as it can be exactly replicated by any other researcher. Generally the more characters you can use the better, I'll list the ones I'll use below shortly.
The other thing that is useful is one or two 'outgroup(s)'. These help root the tree, and ensure the characters you're picking will split closely related organisms rather than working because they're completely independent of everything. For example if you chose red and blue as character states for cars and you had motorbikes and ships as outgroups, it would probably show up as a bad character. Outgroups shouldn't be too far removed from what your studying (eg if your studying cuttlefish then a jellyfish would be an inappropriate outgroup, but an octopus is closely related but different enough to work well).

So for the sweets example, we'll start out with 6 chocolate bars (in this case we'll use a Milky Way bar, Mars bar, Snickers, Violet Crumble, Crunchy and a Flake) and one lolly that isn't a chocolate bar as our outgroup - say a lolly snake.
From these 7 'organisms' we need to find characters that will split them up and hopefully place closely related 'species' together.
So our characters (and their states) might be:
1. Chocolate coated (yes/no)
2. Nougat present (yes/no)
3. Caramel present (yes/no)
4. Honeycomb present (yes/no)
5. Nuts present (yes/no)

So these 5 characters would be enough to split up the chocolates, but probably not enough to completely resolve them to separate 'species'. To draw the tree from these characters, you first need to make up a character matrix. In this case it's pretty simple, as we've got a binary character set (all of the answers are no, which we'll code as a 0, or a yes, which we'll code as a 1). You can have as many states as you need - up to 4 or 5 can work well - but too many may make the character useless. Often matrices are polarized so that all the outgroup scores a 0, but in this case that happened anyway so isn't necessary.

Anyway, our matrix looks like this:

(I used letters for the individual 'species' as it shortens the name and is easier to put on a tree)

So to draw a tree, we start out with whatever character is common to most species. In this case it's being chocolate coated (character 1) which splits the outgroup off immediately (diagram below - sorry for crappy quality, I don't have time to do them properly!). The character used to split the tree at that point can be indicated with a horizontal like and a number, it allows you to see exactly which characters separate species. Everything that occurs after that number has that character, so from the 1 on the tree below, we can see that A does not have any chocolate, but B, C, D, E, F and G do.

So the next step is to do the same thing again, with the remaining characters. The next one shared by most of our chocolates is character 2, which is containing nougat. So this splits off 3 species, shown below:

We keep going the same as before, looking at the next character that is common to BC and D or EF and G (as they're the biggest groups remaining). We'll use character 3 (caramel) next:

And to split the other big group, we'll use character 4 (honeycomb):

And now we'll use our last character, 5 (nuts)

So this is the final tree. It's ok, but not fantastic. We can see that A, E, B, C and D are all separate species, but we've failed to split F and G on the characters we used (both have chocolate and honeycomb, but that's as far as we got). If we were to use genetics as well, we might get further here. If we took brand to equal genus, then F and G would split nicely (VC= Nestle, Crunchy=Cadbury). I'll now colour-code branches according to brand:

Outgroup is green, Cadbury are purple, Nestle red and Mars are black. So in this case the Nestle bar was a good example of convergent evolution - that is two organisms evolving independently in similar environments that end up looking similar but are completely unrelated. It also shows that problems can arise if you use morphology alone - without the 'genetic' info here we couldn't split them at all. Just remember, things that are only one join (node) apart are most closely related (eg in this one C and D are more closely related than D and B or C and B).

This was a reasonably simple example, with only 5 characters across 7 'species' and realistically only one option for the best tree. However if you throw a few more species and a few more characters into the mix, there become multiple options as to what the tree could look like, and because of this it is easiest to use computer programs to try re-combinations hundreds of times rather than doing it by hand.

So that is how you draw a phylogenetic tree. Hopefully it helps in understanding how they come about, and how to read them. You'll come across terms like monophyly and paraphyly, which I might go through in a future post (for a definition right now, google a taxonomic dictionary ;) ), but it should hopefully be easier to understand relationships between species by looking at these diagrams.


One final note: if anyone has any questions or comments, feel free to ask away. I'll try to answer as best I can ;) Also if you've something you're interested in for a post about, let me know and I'll see what I can do... Perhaps next time for something different I'll write about the long-awaited 'talking' trees ;)

Plant of the week #5

Leptospermum myrsinoides
(heath tea-tree)

A brief description: A common shrubby species throughout it's range, the heath tea-tree grows to about 1-2 meters in height. However it is often found as an understory shrub in Eucalyptus woodlands and is much smaller. The 5-petal flowers are white (sometimes pink) and appear in spring.

Taxonomy: From the same family as the Eucalyptus genus, Myrtaceae, it is one of about 85 species. Most species are endemic to South-Eastern Australia, with one found in New Zealand and another in Malaysia.

Distribution: SA, VIC, rare but reported in NSW (mostly in the SE).

Conservation status: Locally common in SA and VIC, not considered at risk in the wild.

Interesting things about tea-tree: Various species in this genus are commercially important for the garden industry and also for honey producers. Dense plantings of tea-trees are popular as hedges and there are many cultivars that are common garden plants (particularly due to the drought-tolerance of older plants). Honey made from the nectar of some species has been found to have antibacterial and antifungal properties.