A thrip's journey to the centre of the flower

Late last year, after a few-month hiatus in posting anything here - an odd consequence of finishing up as Director at Royal Botanic Gardens Victoria, finding I had more time on my hands alongside a fear of whittling it away - I refashioned Talking Plants into a blog about oaks.

That served me reasonably well as I wrote chapters for my 'book about oaks', allowing me to test my hand and my knowledge. I got some useful responses and corrections - thank you - and found plenty of untidy writing among what I had thought was final copy for the book. 

That project continues, so you may get more posts about oaks. However, I'm hoping/planning/wanting to supplement these with stories about other plants. I thought that rather than open up again to all aspects of the botanical world (plants, gardens, the occasional alga and fungus), I'd narrow the focus a little, but this time to flowers.

Flowers, of course, are the reproductive organs of a flowering plant. A remarkably successful way to facilitate the mixing the genes between two individuals of a species, allowing flowering plants to become the dominant form of plant life on land. 

Flowers are also often pretty to us. They may smell nice. Many look good in a vase.

My interest is part aesthetics, part botanical curiosity (as always) and part opportunism. The opportunity, I hope, is to do as I did for oaks. So yes, I am writing a 'book about flowers'. It's further off than the oak book but I need to get started.

I'm hoping that by posting a few photographs of flowers, along with what I can find out about why they look like they do, this will help (me at least). Sometimes, I might be led by a new scientific discovery. Sometimes by a flower I find in a local park. Sometimes, something else.

My posts may be rather short (although this one isn't!), so that I can spend more time on my other writing, and on life. They may also continue to be rather sparse, so that I can ... 

Anyway, I'm very aware there is no need in a personal blog to justify or explain my rationale for posting. From my side, I find constraints helpful in stimulating creativity. From yours, I hope it helps explain why you find the things you do in this blog. 

Oh, and today's flower is what I call Napoleon's jellyfish and others call sea anemone, Napoleonaea vogelii. I've posted on this species before but in researching for the 'book on flowers' I discovered I hadn't fully understood its flower. So let me try again.

*    *    * 

So, what the hell is going on here? That’s not an uncommon question when you work in a botanic garden, surrounded by plants of all sizes, shapes and inclinations. Usually, a little peeling back of layers or plucking of floral parts, will reveal the fundamental arrangement of a flower, the concentric rings of sepals, petals, anthers and ovary as you work inwards. Other times, entire elements are missing, sometimes they are fused together.

The flowers of Napoleonaea vogelii, seem to defy categorisation. Recent authors describe the flowers of Napoleon’s jellyfish as ‘deceptively complex’ and ‘among the most complex [in] extant flowering plants’. That complexity results from adaptations in response to insect visitors, ‘whether they pollinate the flower or not’. That is, pollinating and non-pollinating insects are thought to have influenced the form and function of this truly amazing flower.

French botanist Palisot de Euvois named this genus in 1804, the same year Napoleon Boneparte crowned himself Emperor of the French. Perhaps appropriately, given the complexity of that event and the entire life of Napoleon. I’ve attached the word jellyfish to my common name because that’s what the flower looks like when it hovers above you in the Tropical House. 

There are eight species of Napoleonaea, all from Africa, with Napoleonaea vogelii the most common and widespread. 

The simplest description of the flower (of Napoleonaea vogelii) I can provide, is a blowsy brandy balloon – mostly white but blushed with pink towards its rim – surrounded by a soft spiney white choker, all set against a frilly and fan-folded (plicate) ruff which some authors have aptly called a cocarde. The sexual action and apparatus all lie within the brandy balloon. Oh, and I should mention these complicated flowers emerge directly from the trunk of the plant, a phenomenon we call cauliflory.

I’ve seen only one flower, up high in a small tree inside the Tropical Glasshouse at Royal Botanic Gardens Melbourne. It was around midday, and the ruff was pushed back hard against the bark with only the puffy brandy balloon to be seen from my vantage point.

More technically, the brandy balloon is called the inner corona. Outside it is a the spiney choker of corona threads and then the frilly ruff, called either the outer corona or the petals. So, what then is a corona? A corona is anything that looks like a crown and is most used to describe the glowing ring of the sun around the shadow of the moon during a lunar eclipse. In a flower, it is restricted to a ring of some kind between petals and stamens, often formed – as in this case – from tissue of both. The best-known example is probably the yellow tube in the middle of a daffodil flower. 

In the most recent interpretations of this flower structure, the frilly ruff is considered to be a ring of fused petals – a corolla rather than a corona. Flowers begin opening in the middle of the night and the ruff spreads flat by morning and becomes further reflexed as the day progresses. This then triggers the release of the brandy balloon and its spiney collar around mid to late afternoon, revealing plentiful nectar is what is called the ‘outer staminodal chamber’ (between the intermediate and outer sterile stamens). Peak insect activity is around the middle of the day, at the time the flower’s chocolaty scent is strongest, including moths, leaf-beetles, weevils, ants and thrips. 

This smorgasbord of insects is faced with quite an assortment of barriers. Firstly, an outer ring of about 50 reflexed sterile stamens (staminodes), then an intermediate ring of 40 erect sterile stamens, and finally an inner ring of five pairs (10) of fertile stamens, each with a single anther and alternating with five pairs (10) of sterile stamens. Most insects can fly over or through the two outer layers, perhaps feeling a little protected from the outside world as they devour the nectar. 

The sterile stamens in the inner ring are there to do something that might seem rather perverse – to obstruct the passage of (some) insects to the ovary, which lies within that profusion of stamens and beneath a pentagonal stigma. Only tiny thrips can make it through the final barrier of stamens to reach the inner sanctum. They accumulate pollen on the underside of their body, ready to deposit in the next flower if they walk across the surface of its stigma. 

Each flower is open and attractive for only 24 hours, and on any given day, there is usually only one flower on each tree, so thrips will most likely next visit a flower on a different plant. The other insects – such as moths and ants – don’t seem to be involved in pollination but may protect the flower from insects that might feed on the flower itself. In any case, Napoleon’s jellyfish seems to segregate insects rather than totally exclude some of them from its flower.  Resulting in a flower of wonderous complexity.

Note: references to the scientific literature used to write this piece will be included in the 'book about flowers'.