Melbourne's Biggus Bloomus may be first festive flowering of Titan Arum

In anticipation of my arrival in March, Melbourne's Royal Botanic Gardens has joined a rather exclusive bragging club. By year end Melbournians will enjoy, for the first time, the enormity and smell of the Titan Arum, the world's biggest bloom.

When the first Amorphophallus titanum flowered at Sydney's Royal Botanic Gardens we printed up t-shirts and signs with the slogan 'size really does matter'. It was fun at the time and appealing to, as I now understand, the unflagging English tradition of double entendres and sniggering smut - the 'Are you being served?' legacy.

Every time a Titan Arum flowers, size matters. We measure our spadices - the giant banana part of the bloom - and weigh our tubers - the potato like mass underground. The top picture is from the Royal Botanic Gardens Melbourne Facebook page early this week, showing how you should measure your specimen.

The largest flowering in cultivation seems to have been at the University of Bonn Botanic Gardens, in 2003, reaching 2.74 metres in height and with a tuber weighing in at 78 kilograms. Three years later they had a bigger tuber (117 kilograms) but it decided (unusually) to produce three successive blooms, none of which reached the above-heady heights of 2003. The reference cited here mentions a record bloom height of 3.06 metres but I'm not sure if that's in cultivation or the wild.

At Royal Botanic Gardens, Kew the biggest bloom reached 2.48 metres and since I've been here we've had a few come close to that, including one last summer getting to 2.32 metres - this is the bud, which I never saw unfurled.

There was another whopper in flower when I came over in 2010 to be interviewed for my current job. I was impressed then how much bigger it seemed than the ones we'd grown in Sydney.

But this week it's all about Royal Botanic Gardens Melbourne as they ready to expose their first Titan Arum bloom to the world. The bud had reached 1.62 metres in length the last time I checked Twitter and Facebook (21 December). The tuber was 35 kg, big by Australian standards. Sydney horticulturist Gareth Hambridge, tells me the biggest tuber grown at their (and at the time my) Royal Botanic Gardens was 26 kg, producing a 1.98 metre bloom. That was in 2008.

This next picture is of me (slightly out-of-focus) in 2006, next to a decidedly diminutive Titan Arum bloom and shaded by the leaf of another Titan Arum, with our wonderfully named Sex and Death exhibition banner (advertising orchids and carnivorous plants) behind me.

The plant flowering now in Melbourne started as a one kg tuber sent from Sydney around 2006, when I was Director there. Sydney's plants can all be traced back to some seed collected from Sumatra by Wilbert Hettersheid, travelling with John Symon and the a rather more well known chap, David Attenborough. While I had assumed the seed came to Sydney via Kew, Sydney aroidologist Alistair Hay assures me he was sent the seed directly by Wilbert. You can see a picture from the Sumatran collecting trip in this University of Wisconsin-Madison page about their offspring from the same source.

So the Melbourne bloom has a nice pedigree and is likely to be one of the bigger (biggest - not sure about Cairns who have had one or two) blooms in Australia. All this begs the question of why the Titan Arum produces such as large bloom. Clearly the 'big bang' evolutionary strategy has worked; up to a point given it is now under threat in the wild.

Each plant builds up huge food reserves in its tuber over seven or so years and starts to produce giant blooms every few years after that. Each bloom is very big, very colourful and very smelly, so hard to miss if you are a pollinating insect. And if fertilised, there are plenty of fruits as you can see in these pictures of one of Kew's five successful blooms over the last year. And just think of the offspring of Hettersheild's seeds, gathered from a single bloom.

If you want to see Melbourne's bloom with its spathe (the maroon skirt) fully expanded and the stench at its most powerful, Gareth predicts New Year's Eve. The locals are hoping for Christmas Day. Yesterday Melbourne reported the skirt was colouring up nicely, so I'll go with Boxing Day. Will this be the first time a cultivated Amorphophallus titanum has flowered during the 12 days of Christmas?

There is always something to be competitive about with the Titan Arum. Which reminds me, this last picture shows the closest I've got to seeing a Titan Arum in full bloom at Kew. Plenty of time for another really big flowering before I head to Melbourne.

Note: The Titan Arum bloom is sometimes called an inflorescence. It's a collection of highly reduced flowers in a specialised structure that to all intents and purposes is a flower. Bloom seems nice and neutral, if a little daggy.