Thursday, 3 February 2011

I see red

If you have to associate one colour with plants, it would be green of course. That’s why we have the Greens, the greenery, how green is your valley, and so on.

But there are plenty of exceptions, including plants with red streaks, yellow flecks and some almost entirely brown or purple. You may remember I suggested a while back about the ideal plant for outer space might be black or purple.

Today I want to talk about a few red things in our lives that are coloured by plants, or plant-like things. This is a topic I also covered in The Gardens, magazine of the Friends of the Gardens, but in my quest to make this blog the source of all (my) botanical wisdom I include it here as well.

A few years ago I got to (finally) see some wild pink flamingos in southern France. Flamingos are pink because they eat pink crustaceans and algae (Zoo flamingos have to be fed carotenoid supplements to keep them well flushed).

Algae, particularly seaweeds, are commonly divided up into red, green, brown and blue-green algae. There are lots of other hues, such as yellow-golden, yellow-green and so on, but those are the big four.

So you might expect the pink algae eaten by pink flamingos to be, well if not pink, red. Red they are, in colour but not classification.

The colour names for algae are common names, like ‘blue gums’ and ‘meat pies’. The trouble is that colour isn’t always a reliable identification marker. The freshwater red algae, for example, are mostly olive green or brown. The defining pigments, correlated with biochemical pathways and life cycles, are sometimes masked by other chemicals.

The pink algae behind the pink flamingo is most likely a blue-green alga (or more correctly a blue-green bacterium) called Spirulina – also a popular ingredient in some health store concoctions – or a green alga called Dunaliella – grown and harvested in salt lakes to produce B-carotene to colour margarine, among other things.

In the same vein, red snow is usually red due to a surface bloom of a green alga called Chlamydomonas. And red tides are caused by dinoflagellates, complex algal organisms unrelated to any of the four major groups described here and more often brownish in colour.

On a recent visit to the fantastic Alice Springs Desert Park, I was tantalised by a sign that said fungi play a role in the red colour of the desert sand. Fungi are more closely related to people than plants, but we often thing of them as part of the plant world and we have fungal experts working at the botanic gardens.

In any case, according to this sign, your typical quartz sand grain (like you’d find on a Sydney beach) is covered in a thin coat of iron salt in the desert due to the chemical activities of a fungus. I look forward to learning more about this, and the colour red.

Image: Extremely pink/red/orange flamingos in the Hong Kong Zoo. *This posting is from the Radio Archives (October 2008).

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