Titan Arum's honorary flower

When the Titan Arum blooms - as it does regularly in glasshouses all over the world these days - botanic gardens' spokesfolk, such as me, employ all kinds of linguistic contortions to describe the structure of the 'flower'. This gigantic thing is a collection of tiny male and female flowers, with some fancy trimmings.

As most people now know, when the swollen green 'flower-bud' opens, a purple pleated skirt is unfurled, exposing the lower half of a yellow banana-shaped object that seems to have the texture of chamois leather. A powerful and rank smell rises from deep within the now skirted banana, attracting in its native land of Sumatera various flies and beetles. In botanic garden glasshouses, the descriptively named Amorphophallus titanum attracts people, as you can see here in Sydney Royal Botanic Garden's Tropical House a few year back.

The object of desire is either the world's biggest cluster-of-flowers or the biggest unbranched-inflorescence (an inflorescence being a collection of flowers and associated bits and pieces). For the botanically inexperienced, or perhaps willfully radical as I'll argue, it's the world's largest flower (but see also Rafflesia).

This is our most recent bloom in Melbourne's Royal Botanic Gardens Tropical Glasshouse. It's the third time a Titan Arum has flowered for us, and the second time for this particular tuber (the first flower was in January 2013, a month after its Christmas flowering sibling). Our tubers came from Sydney's Royal Botanic Garden and their plants started as seed collected by David Attenborough and Wilbert Hetterscheid in Sumatera in 1993. The tip of the banana was 233 cm above the ground late yesterday; impressive, and closing in on the biggest recorded in Australia (Cairns had one at 238 cm in 2014), but well short of the record of 290 cm for a plant in cultivation. We expect the thing to open fully in the next few days, perhaps putting on a few extra centimetres on the way...

But what do we call this huge and impressive infrastructure, home to thousands of tiny flowers, or florets as we sometimes call small flowers of this kind? Each one consists of either a single bottle-shaped pistil (this is the stripped away female part of a female flower, including the ovary in the bottom of the bottle, a stalk called a style and a sticky blob on top called a stigma) or a single stamen (in this case a spherical sack of pollen).

None of these flowers/florets are garnished with petals. The pistils (female 'flowers') are in neat rows at the bottom and fire off together - sorry, they become receptive all at the same time. The stamens (all that there is of the male 'flowers') are packed in at the top and release pollen together. So although technically the skirted banana structure is a collection of single-sex flowers with some very fancy accoutrements, if the whole thing looks like a flower, behaves like a flower and smells like a...dead possum...let's call it a flower.

I would argue, following the lead of an expert in this family, Dr Alistair Hay, that the floral bits are so reduced as to be equivalent to organs within a larger flower and the skirt (spathe) and banana (spadix) work in the way any other flower does in attracting pollinators to the receptive parts of the flower(s). In fact the Kew Plant Glossary helpfully describes a flower as 'an axis bearing one or more pistils or one or more stamens, often with parts to make it more functional or more attractive to pollinators'.

Now of course you could argue the same way for any inflorescence or collection of flowers but, I would suggest, rarely as coherently as with the Titan Arum bloom. It certain teeters on the edge of being a flower or an inflorescence.

Maybe the solution is to give this spectacular and fascinating structure honorary flower status. I can see parallels with the debate over Pluto's planetary rank although I'm not sure it helps my botanical case to read that Pluto may soon return to full planet status after having to endure the floret-like moniker of 'dwarf planet' for the last nine years. That aside, the 'largest unbranched inflorescence in the world' is just lame.

Images: The unopened Melbourne flower, with close-up of skirt/spathe at the top, come from a stock of images taken by David Robbins, Robyn Merrett and me. The carved plant and close-ups of pistils and stamens, plus the following picture of a spent flower with its inside-out skirt looking like a breezy coiffure, I took in 2007 at the botanic garden (Keban Raya) in Cibodas, Indonesia. The open flower (!) above, with a visiting man, is from Sydney in 2008.

Feedback: Dr Phil Garnock-Jones from New Zealand suggests the term blossom. He says in a tweet (10 March 2015): "Excellent. I'd call it world's biggest blossom. Many flowers, 1 blossom; cf. an iris, with one flower, 3 blossoms" Has some merit.

And further information?: See and hear me talking about the flowering of the Titan Arum in Melbourne on 13 March 2015, with excepts from this post about whether it's a flower or group of flowers, on RN website.