Christmas Bells

Christmas Bells
Christmas Bells - Blandfordia nobilis

Wednesday, July 22, 2009

Sassafras flowers - a detailed presentation

Sassafras flowers are blossoming all over Robertson at present. I mentioned them coming into flower, last week. I am still not able to bring you the sensation of their sweet perfume, unfortunately.At the time I wanted to go into some detail of the strange structure of the flower, but I could not find out enough information to enable me to explain them to you. Tonight I think I am ready to try.
Kindly bear with me, dear reader. I have never before seen any flower with the structure which you are about to see.

Sassafras flowers develop in threes.
One single flower in the centre,
and two buds which will develop as the first flower fades.
Here is a single flower - cropped.
It is about the size of a small thimble
just large enough to take my little finger.
Note the circle of thin stamens.
Each stamen has a pair of prominent white swellings at the base.
As I shall explain later, those swellings are the anthers,
but the pollen within them is not yet ripe - not ready to be dispersed.
Another flower - picked, and ready for dissection.
Here is how the flower (inflorescence) is described by botanists. This is sourced from "Forest Trees of Australia". Click to enlarge image so you can read the text.
The dissection commences. I have removed several petals ("perianth lobes") so you can see into the flower, from the side view. Note the fine needle-like structures which are the stamens of the flower.
Click to enlarge the image. Note the fine downy hairs on the petal surface and on the outside of the swollen base of the flower (ovary capsule). It is this part of the flower which swells into the seed capsule, and from my memory of the previous seeding explosion 3 years ago, those seed capsules are noticeably hairy as they develop. In fact their hairiness is significant, for the seeds are wind dispersed, and anything which helps catch the wind is important to successful seed dispersal.

This is the same image, having been worked over somewhat in Photoshop.
The point is to simplify and thus reveal the important features of the structure of the flower.
What you have left are two of the 6 stamens, each with the two prominent anthers, which are developing to maturity - preparing to shed pollen (dehiscing). There is a structure holding the anthers out to the side to the flower - at right angles (more or less) to the tall, upright pointed stamen. That structure is made more clear in a botanical illustration and a photo below. The pollen grains are held in the anthers. that is normal. But its location at the bottom of the stamen is far from "normal" amongst most "modern" plants. In fact, the botanists regard Sassafras as a primitive plant, (amongst dicotyledonous plants) largely based upon an analysis of the flower structure. That is, it is not regarded as "primitive" compared to ferns, etc. But compared to other flowering plants, it is so regarded.

This location of the anthers (and therefore the pollen) is very different from most plants with which we gardeners are familiar. For example Lilies, or my favourites, Peonies, which hold their pollen high within the flower, to maximize pollen collection by bees.
A pink trumpet Lilium
with pollen very prominently presented on the anthers.Here is one of my favourites, a Tree Peony.
Note the ring of anthers with heavy pollen.
Clearly the Sassafras plants have evolved a very different form of pollination. I recall reading that they are supposedly pollinated by Mosquitoes (perhaps small midges or gnats which I have noticed around in the last few days.) The pollen grains are close to the base of the flower, not at the tip of the stamen, which is the more familiar position.

Here is the "eye" of the flower, cropped close.
(Click to enlarge the image).
Note the ring of 6 stamens forming the outside ring of the central part of the flower. Some are pointing up towards the camera, so they disappear, somewhat. But you can clearly see the 6 bases of the stamens, each with two white bubbles of pollen on the anthers.
There are two dark spots on the base of each stamen.
Inside that ring of stamens are a series of small structures, which are the the "6 alternating shorter staminodes" referred to in the botanical text above. Staminodes are modified stamens, often infertile (having no pollen).
These structures are visible against the green base of the flower.
Right in the centre of the flower are the thin white, pointed carpels (the female parts of the flower).

Here is a botanical drawing of the structure of the stamen and anthers of the Sassafras.
And here is an image of a single stamen and the paired anthers at the base - the result of my "dissection". The green section is the remains of the base of the flower - acting as a handle for my fingers to hold the stamen - allowing its details to be clearly seen.
You can clearly see the pollen ready to be dispersed (a process known as "dehiscence"). If you glance back up the page to the third image, you see a photo of a very fresh flower. Examine the anthers in that flower, at that stage of development. They are hard and white and clearly are not mature - at that stage. The pollen had not yet started to dehisce in that image. Unlike the pollen in this image.

In due course, I shall show some seed capsules and then the actual seeds when they disperse.


mick said...

Beautiful clarity and detail on all your photos. I now know from experience just how hard it is to achieve shots like that!

Denis Wilson said...

Hi Mick
You flatter me. As you know, there is always a trade off between having the bit you want to discuss in focus and clear - and losing other details because of depth of field issues.
Strangely structured flowers, though. Quite unusual.

Snail said...

Excellent post, Denis. I'm learning plenty about plants here!

Denis Wilson said...

Hi Snail
Shall we see you converted to botany?
Perish the thought.
The local snails will start devouring the plants if they hear that rumour?