Saturday, 25 April 2009

First to Flower

This gorgeous picture of Amborella, sometimes touted as one of the 'primitive' flowering plants, is from a website devoted to the genus (I'm not vouching for the site, just the images)

In my Darwin talk yesterday, I mentioned that one of our scientists at the Botanic Gardens, Dr Peter Weston, had said (when prompted...) 'If I met Darwin today, I'd tell him that we have worked out his 'abominable mystery' - that is, the origins and the family tree for flowering plants'.

After the talk I was asked for the solution to the mystery. A very fair question! For the family tree for flowering plants you are best directed to the Tree of Life web project. Type in 'flowering plants' and you'll be taken to that part of the tree containing the angiosperms.

You'll also see, in the first branches that part of the tree, part of the answer to the origins of the flowering plants. The only problem is that the question 'what did the first flowering plant look like?' has become a hard question to answer. We used to say something like a magnolia. That was quite easy to say and we would add that the family Magnoliaceae was one of the most 'primitive' families of flowering plants (along with Winteraceae and others).

The trouble with that answer is that every plant today has the same evolutionary age as every other plant. You can trace them all back along the Tree of Life to a split from the green algae. Some parts of the tree are profusely branched (e.g. the eucalypts), with lots of species having evolved and survived today. Other branches are spindly and hardly branched (e.g. the Wollemi Pine) - their sister species have either gone extinct or else they have not had to change or adapt much over time.

So what about this 'first' flowering plant. Well we can surmise it would share the characters that all the bottom branches have in common. That is, they evolved further but what links them together are the shared characters from their ancestors. We can also use fossils to get a glimpse at the earliest plants with flowers.

I took a stab at explaining this a few years ago (2003), talking with Angela Catterns on the 702AM Breakfast Show. This is how I put it then:

Botanists until recently thought the first flowering plant to evolve (after the age of conifers, some 130 million years ago) was something like a magnolia: a tree or shrub, with large flowers made up of many circles of petals and stamens. It seemed a natural progression from a tree with pine cones.

Now there are two alternatives: both far less attractive than the magnolia.

1. A swamp herb: A weedy aquatic herb (Archaefructus), preserved in 125-million-year-old lake deposits from NW China, has been hailed as the first flowering plant on Earth. It looks like a cross between common pondweed and the Watermilfoil (another aquatic plant, with finely divided leaves) – it has two sorts of leaves, like many aquatics.

Where this Chinese fossil fits into the flowering plant family tree is still uncertain [at the time I was speaking to Angela, at least]. If is it down the bottom somewhere, it suggests the first flowering plant had flowers without petals, it wasn’t woody and it grew in a swamp (not a great horticultural specimen!).

2. Something like a New Caledonian shrub with tiny flowers: The second way to trace the first flower plant is based on DNA evidence from living plants. Fossils are like odd bits of a jigsaw puzzle but the history of life is being carried around in the genes of all plants and animals.
This line of evidence doesn’t give us a single ‘missing link’. We have to create an identikit picture of the first flowering plant from living ancestors that have hardly changed over millions of years of evolution (like the Wollemi Pine, which is a conifer rather than a flowering plant).

Using the latest genetic evidence, there are four groups of plants that come from the bottom branch of the evolutionary tree. They include water lilies, the anise oil family, and vines and climbers that grow in northern NSW and northern Qld. Together they are often called ANITA, an acronym from their scientific names.
One of the most interesting members of the group is an obscure New Caledonian shrub with tiny flowers, Amborella. A few years ago, it made front-page news in the New York Times as the most primitive flowering plant alive [which, as I said at the start of this post is a meaningless statement].

The identikit picture of the first flowering plant from ANITA is a shrub with very small flowers (it has petal-like bits, but they are tiny!) that are insect pollinated. Small flowers, but ‘woody’ rather than a soft aquatic herb.
Interestingly, even if Archaefructus is correctly placed, there are many of these ancient lineages in the Australian region. This is probably because conditions have remained favourable here for something like 70 million years and there have been less opportunities for aggressive invasions of plants from other regions.

2 comments:

Asyncritus said...

Heh heh heh!

Ignorance rules OK, doesn't it!

Imagine Weston's effrontery (or is it stupidity?) in even thinking the problem has been solved!

So guys, did God make the angiosperms in one go, or did they 'evolve by small steps' and from what?

How did the ovary get INSIDE the sporophyll from OUTSIDE as in the gymnosperms???

Tim Entwisle said...

I think it's amazing that we can narrow down the options so much and get so close to tracking scientifically (particularly in DNA and current look of the plant) what anscestors must have been like. Exciting and raising even more questions - exactly what science is about!