Tuesday, 15 December 2015

Christmas lantern a leafless plant in bud

A Christmas Lantern from the plant world! It's a flower bud, less than a centimetre long, produced by a plant with no leaves and never rising above the leaf litter. The Christmas conundrum is, how does it do it?

There are two main ways a leaf-less plant can survive in nature. Unlike a fungus, a flowering plant can't generate it's own food directly from discarded or dead parts of other plants and animals; that is, it can't be a true saprophyte.

The most common survival method is to attach itself to another plant and become a parasite (or perhaps like a mistletoe, a hemiparasite, where you keep some leaves and do a bit of the hard lifting yourself).

The other is to cosy up with a fungus, which we call mycoheterotrophy. In this relationship the plant's food and nutrients come from the fungus, which gets them from somewhere else such as decaying organic matter or another plant.

I've been lucky, or unlucky, enough to see an extraordinary example of each in bud, but not if full bloom. Lucky to see them at all, but unlucky to not experience the full unfurling of the flower.

The extraordinary parasite was Rafflesia keithii, a bud or two of which I saw on the Crocker Range, near Koto Kinabalu in the Malaysian state of Saba, on the island Borneo. I was on a family holiday in 2004 and these are the closest we got to seeing what at up to one metre across is arguably one of the largest flowers in the world.

Surprisingly, Rafflesia is in the family Euphorbiaceae along with things like Poinsettia and rubber trees, but that doesn't tell you much about its life strategy. The seed of a Rafflesia germinates on its host, a species of the tropical vine Tetrastigma, possibly depending also on fungal partners to get going. The parasite sends out threads that penetrate into the woody stem of the host and spread throughout the vine.

At flowering time the parasite bursts through the barker outer later and produces a cabbage like swelling. From my reading of Rafflesia of the World published in 2001, and a little web surfing, it seems we still don't know much about what happens between germination and flower bud initiation. Pertinent to this post, though, we do know the bud gets its food directly from the host plant.

At the other end of the flower size spectrum for leafless plants are these little raspberry like flowers, called Fairy Lanterns, or Thismia. There is only one species of Thismia in Victoria and it seems to be scattered here and there in deeply shaded forest. It's a mycoheterotroph, living its whole life beneath the leaf litter and getting food from another plant species, but indirectly... When the seed germinates it has to be in contact with an appropriate fungal species, which then becomes it's permanent life support system.

That fungus already has a mutually beneficial relationship with nearby trees (it's called a mycchorizal partner) so the carbohydrates that end up fueling the Thismia originate in a nearby tree, with the fungus effectively providing a transport system between the two plants.

In the case of the Thismia rodwayi buds I saw this year, in November, that tree was mostly likely the Musk Daisy Bush, Olearia argophylla. The Thismia flowers, when they open, are most likely pollinated by insects rummaging through the leaf litter. The seed is presumably spread by the same bugs, or perhaps by marsupials.

With four other genera Thisma is now generally included in the family Thismiaceae, rather than Burmanniaceae, and despite my earlier post on Thismia, thought to be not particularly close to the orchid family. Which is fine because it does seem to have little to do with orchids, other than being the kind of plant with a flower you might spend a day looking for but return home strangely comforted by some beautiful images of leaves and buds.

Images: the Thismia bud pictures are from the Otway Ranges on 3 November 2015, under the guidance of Neville Walsh (with his head down here searching for a flower under the leaf litter), the Rafflesia buds from the Rafflesia Centre at Tambunin, Saba, taken in July 2004.

Coming up: For the next six weeks you can listen to Talking Plants (or something like it) on Radio National. I'll post a reminder each week here, listing guests and topics, and you can listen or podcast from the RN Talking Plants website.

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