Christmas Bells

Christmas Bells
Christmas Bells - Blandfordia nobilis

Saturday, June 27, 2009

Protea flower parts - in detail.

Several weeks ago, I showed some lovely flowers of a popular hybrid Protea "Pink Ice". Here is the primary parent plant of that hybrid.

According to the website, Protea neriifolia was the first protea ever to be mentioned in botanical literature. It is a South African plant (of course). It was first discovered in 1597, and was apparently was first illustrated in 1605. It was described and named in 1810. The name refers to the similarity of the leaves to that of the European plant - the Oleander (Nerium sp)Today it is my intention to examine the details of these spectacular flowers. Of course, in Australia, we have many plants (Waratahs and Banksias and Grevilleas to name the most familiar) which the botanists recognised easily as related to the Proteas - hence they are referred to as members of the Proteaceae family. However, to the untrained eye, the differences are more apparent than the similarities. I wish to concentrate tonight on the similarity of flower structure (with some of our flowers).

When I started this investigation, the first thing I felt was "odd" was the tuft of little "feathered tips" in the centre of the Protea flower. Then I decided to pull out several of these flowers to examine them in detail. Two things happened. The flowers broke off half-way down, with a long thin tube still protruding down to the base of the "flower" (the entire head, I mean). Clearly that would have been the tube through which the pollen grains grow down to the ovary at the base of the flower. The second thing was that my fingers were suddenly covered with pollen, which surprised me, for I had been looking to see where the pollen grains originated, but had not seen them. At least I knew they were there somewhere. Time to look more closely.
Firstly you need to understand that what we see as a flower in in fact a composite flower structure - which is composed of many flowers grouped together inside a set of surrounding bracts. It is the bracts which we see as the main part of the flower - but in botanical terms, the bracts are mere "window dressing". They simply serve to protect the true flowers as they develop.

A Protea flower - an individual "true" flower I mean - does not have separate sepals and petals. Instead, there is one set of four perianth segments (called tepals). Initially these parts are fused. As the flower matures, it ruptures open.

Following up from my first experiment to pluck out a flower (which did not work), I realised I had to break open an entire flower head (removing some of the external bracts), to approach the many flowers from the side. That worked, and in the next image, you can see the "feathered tips" of the tepals, close up.

You can also see the lipstick pink tips of what are similar to our Australian proteaceae flowers - the "pollen presenters". Technically, this is the tip of the style. It is the female organ of the flower, but it acts as the male part of the flower temporarily. That will be familiar to readers of this blog - for it is the secret to their pollination.
This is one of the things which the Proteas have in common with our own Proteaceae flowers, although our plants tend to have a curved flower, and a style "pops out" to the side, under pressure.
This Protea style does not to have that curved shape - just a slight bend near the tip, visible here, just below the red coloured section.
The four tepals are fused into a long narrow tube with a closed cup at the top. (That is the bit which has that feathered external appearance). Inside the perianth, the four stamens are fused to the tepals, in such a way that the anthers are enclosed within the cup. The pistil initially passes along the inside of the perianth tube, so that the stigma too is enclosed within the cup. As the flower develops, the pistil grows rapidly. Since the stigma is trapped, the style must bend in order to elongate, and eventually it bends so far that it splits the perianth along one seam. The style continues to grow until anthesis, when the nectaries begin to produce nectar. Just before anthesis, the anthers release their pollen, depositing it onto the stigma. At this time, the perianth splits apart, and the pistil is released to spring more or less upright. Then the tip of the pistil (the "stigma") functions (for several days usually) as the "pollen presenter". Hopefully a suitable pollinator will visit the flower to get the nectar, and will be dusted with pollen. Once the pollen dries, it falls off the tip of the stigma, which then assumes its true female (receptive) function.
You can see the pollen on the Stigma in this image.
(Click to enlarge)
The male organs (anthers) of Proteas are also distinctive. The anthers do not have long stalks (filaments), but are joined directly to near the top of the tepals. Unlike most other plants, the anthers shed their pollen onto the topmost portion of the style just before the flowers open. Because the style presents the pollen in a position suitable for placing onto any visitor, the top-most portion of the style is called the pollen-presenter. The presence of a pollen-presenter is another diagnostic feature for Proteas. It allows the pollen to be "dusted" onto the natural pollinating vector, be it an insect, a bird or a South African mouse (or Honey Possum for Australian members of the Proteaceae).
Note the split in the perianth. That is where the pollen came from. In this regard it is functionally similar to the Waratah and Grevillea flowers. Click to enlarge the image above to see what I mean.

Four nectaries are apparently situated at the base of the ovary, between the ovary and the tepal bases. These secrete nectar to attract pollinators. Source: Protea Atlas Project

One thing which I have not managed to understand yet is why our Proteaceae flowers split into 4 separate perianth segments, but this Protea seems to keep its anthers closed within a single tube - even after the style has split out. From this reference document, it is obvious that many South African Proteaceae do behave in ways more similar to our Waratahs and Grevilleas (than this Protea does).


mick said...

Beautiful flower and great photos and description. I like the way the hand gives an idea of the scale of the flower parts.

Denis Wilson said...

Hi Mick
Glad you like that. Can you grow Proteas on the coast?
Lovely plants.
One of these days, I should talk you into posting close-ups of your Grevillea bush flowers.
They are fascinating up close.
. If you are interested, I can help with the details, if you can get some close-up images.
Follow the Grevillea link in my posting to see what I mean.
Have a think about it. Its a good project to have up your sleeve for a rainy day.
I can be contacted by email, as per my Profile page.

Denis Wilson said...

Hi Mick. This is the url you need to see an analysis of a Grevillea flower. Copy and paste. I cannot make it clickable from here.

Actually click on the hot link in the blog which says "curved flower"
just above the first photo where my hand is.


Anonymous said...

Thanks Denis. The Protea structure and funcionality is no less than uncanny.

tarkineus (BIBY)

Denis Wilson said...

Hi Tark.
Welcome to my Blog.
Glad you appreciated the details of the Protea flower.