Saturday, 30 December 2006

Never casual about Casuarina

In the very first post on A Snail's Eye View, I mentioned my interest in Casuarinaceae, a largely Australian group of trees often referred to as she-oaks. I have 15 species so far. I'm sure I could have accumulated more were I not so lazy laid back about my interests. On my wanderings through the more interesting nurseries (such as Roraima in Lara and Kuranga at Mt Evelyn), I occasionally spot a species I don't have. But I don't go hunting for them. And I don't collect wild seed.

Casuarinaceae are odd-looking plants. They have the standard tree-ish arrangement of a main stem and branches, but that's were the ordinariness ends. There are leaves but they're reduced to tiny triangles. They no longer have a role in photosynthesis. Instead, that job has been taken up by the branchlets, which grow from the main branches.

Each branchlet is made of sections called articles that lie end to end. (I described this in the first post but didn't have a photo to go with it.) You can see the articles and minute leaves in this branchlet from the Tasmanian short-range endemic Allocasuarina crassa. (By the way, everyone should have one of these marvellously sculptural plants in the garden.)

Each article bears a series of ridges (phyllichina) and furrows. The furrows (covered here by fine white hairs) contain stomata, which are pores for the uptake of carbon dioxide used in photosynthesis. Furrows reduce water loss from stomata. Those in the Wet Tropics endemic Gymnostoma australianum (left) are shallow and open, whereas those in Casuarina and Allocasuarina, which live in drier areas, are deep and narrow.

The shape and number of the phyllichnia and their associated leaves are important in distinguishing between species. Here's a third species, Allocasuarina monilifera (another Tasmanian endemic) to give an idea of how this group can vary.

Of course, there are other key features, such as flower, cone and seed (samara) shape but you have to be there at the right time for these to be of great use. The branchlets are present all year round.

If you want to know more about Australian Casuarinaceae, the relevant section in the Flora of Australia is available on line.

9 comments:

Tony F said...

What a great Blog. Terrific writing and excellent links. Keep up the fantastic work. Love the Natural Visions photographs - wow!

Snail said...

Thanks for the kind words!

Aren't those photos at Natural Visions just sensational. Now there's a photographer who understands his subject.

Marcus said...

Casuarina equisetifolia is a cliche here in Singapore; you have roads, schools, luxury apartments and even hotel suites named after it.

Duncan said...

Interesting blog Snail, but you didn't mention the sound of the breeze blowing through a she-oak ;-)

Snail said...

Marcus, Casuarina is a popular name here too. (Wonder if it's the sound of the word?)

I just had a look on the gazetter and found 53 locations with Casuarina in name!

Snail said...

Oh, yes, Duncan! That beautiful whispering sound. Sussuration, that's the word!

tapperboy said...

Spent a few hours twisting articles one section from another while picnicing underneath a stand but never thought for one minute about them not being leaves! I've learned something totally new today. Previously just assumed the articles were the leaves just evolved but the little triangles business is really amazing stuff. Loved always the sound of the wind through them. The bark, spiders love the crannies :) Planted a few tormentosa in the last garden.

Snail said...

I should shove some Casuarina articles under a microscope to get a better view of the fancy bits. (Technical term, there. Hope I'm not getting to high falutin.)

Fernanda Ramírez said...

hello!!! thanks for the info, I´m from Guatemala and i´m trying to determinate a casuarina with the flora of australia, but I don´t understand how it has to look the phyllichina (the begining n_nU).

Sorry about the writting but i´m not good at english.