Friday, October 23, 2015

Raspy Root Orchid

Rhinerrhiza divitiflora

I was surprised to find this orchid in flower, early this week when we were still complaining that there had been no rain for ages. Its reputation is for flowering after rain, but it was undeterred by the very dry weather.
It is also said to prefer a damp, shady site, but this plant looks very healthy in its dry site on the eastern slope of the Range near Toowoomba. It was growing in dry rainforest with a rather light canopy. Its need for shade was apparently satisfied by its situation on the southern side of its host tree.
It is difficult to catch this species in flower, in the wild. All of a single plant’s flowers open within a short time, often on the same day, and last only a day or two, so its flowering season is very short indeed.  Note the buds on this plant, which I photographed late in the morning. I wonder whether they would have been open, if I had gone back a few hours later.

There is also a tendency for all the raspy root orchids in an area to flower simultaneously, so if you are lucky enough to find one, it’s worth looking around for others.

Thursday, October 8, 2015

Slender Onion Orchid

Microtis parviflora 

This humble little fellow must be our least ornamental local orchid. The flowers have tiny “faces” and seem to be almost all ovary.

You have to be paying attention, to notice that they are orchids at all!

However, the minuscule flowers are really delightful, so if you find any, look at them closely.


Not that they are easy to find. (Yes, there are some in the photo below. If you click on it, it will enlarge. Can you find them?)

Some internet sources claim that onion orchids are plants of “bogs and damp places”, but this colony of plants looked perfectly happy today, on an exposed, dry slope on Mt Kynoch red soil. They are said to do better after fires. This particular grassy, cattle-grazed site hasn’t had a fire for years and the plants were thriving. It would be interesting to see how it might be improved with fire.


The plants grow from underground tubers. At first glance they seem be quite leafless, but you can see that each flower stem does have a leaf wrapped firmly around its stem.

Like most orchid tubers, they are probably edible, and their tendency to grow better after fires was one of the reasons Aborigines burned their land. Early white settlers couldn't see why the fires were lit, and believed so strongly that Aborigines weren't farmers that they were not inclined to find out whether these apparently (to them) pointless fires actually had a practical purpose.

These orchids are highly unusual because they are pollinated by  ants.
Ants are normally the enemies of plants, when it comes to pollination. They secrete an antibiotic substance which kills it. (The antibiotic is produced by their metapleural glands, for those who are interested in that kind of thing).
Just to add to the difficulty, some ants’ rough little skins are simply too hard on pollen and likely to kill it.
Plants that need animal help for pollination have evolved flower designs to attract their pollinators, so it is quite interesting to examine just what appeals to ants.
Onion orchids are unique among orchids, as their pollinaters are wingless worker ants - usually little tyrant ants, Iridomyrmex gracilis. There is no question of attracting flying male ants by looking and smelling like a female, as happens with the other ant-pollinated orchids. Colour is clearly not relevant, and it is very obvious that this plant’s pollinators are not being attracted by showy petals!

(Hope you like the photo. It looks like a studio shot, doesn't it? However I assure you that no onion orchid was harmed in the making of this blog. It was held steady with a clothes peg on a stake, and the background is an out of focus trouser leg.)
These little orchids produce a sweet fragrance to attract the ants, and they deal honestly with them, providing the sip of nectar that the perfume promises. Honesty is not something we expect from orchids. Most of them are cheats. They dress up to imitate nectar-producing flowers, even having "nectar guides" - those lines that lead to the centre of the flower - but they don't supply the goods. The trick works for most insects, as demonstrated by the fact that the orchid family is one of the largest plant families in the world. Perhaps ants are not so forgiving as other kinds of insects (or not so stupid as to keep going from one unrewarding flower to another).
Having attracted their ants, the next problem is to deal with their pollen-destroying capacities. These knacky little onion orchids have evolved flowers which organise the nectar seeking ants so they can only get their reward if they are correctly aligned to pick a dab of pollen on the fronts of their faces,  well away from their metapleural glands. The flowers may look small, but they’re bossy!
They also have pollen with short stalks to hold the pollen grains safely away from the ants’ destructive skin.
Onion orchids fit a pattern shown by other types of ant pollinated plants. They tend to have small flowers, each supplying only a little nectar. This means that larger insects are not interested, and that even little ants have to visit a number of flowers to collect enough for their purposes.
They also tend to have flowering stems with flowers that open serially. This means that ants can’t find enough nectar by foraging all the way up a single flower stem, so they have visit more than one plant, carrying pollen as they go.

These little flowers, which at first seem quite boring, have a lot to interest us!

Sunday, October 4, 2015

Copper Beard Orchid

Calochilus campestris

Doesn’t this little old man of the woods have a wonderful face?

We found him (and a number of his friends) in the Merrit’s Creek Road area today. They seemed to like growing among low grass, close to broad-leafed stringybark Eucalyptus acmenioides trees.

Much of this plant’s life is spent underground in tuber form. In spring, it puts up its single long, floppy leaf, usually going unnoticed until it also puts up a flower stem.

Aborigines used to eat the tubers, back in the days when there were considerably more of them.

These flowers are pollinated by male wasps (Campsomeris sp.). Wasp pollinated orchids emit a scent which resembles female wasp pheremones, and, unlikely as it seems, the male perceives this flower as looking like a female wasp. On investigating whether it would make a good mate, he will get dusted with pollen. This is then transferred to another orchid as he repeats the process of attempting to find a mate.

Friday, October 2, 2015

Bluebells - are they Boys or Girls?

Wahlenbergia Species
 Australian bluebells, with their sky-blue flowers, are one of the spring/summer delights of the Darling Downs. They particularly love the bit of extra moisture provided by road runoff, so they are lining many of our country highways at the moment.
One of the few bits of natural lore that my mother taught me was that there are boy bluebells (left, below) and girl bluebells (right).

My mum was not strong on knowledge about native plants. As I grew up I learned to be a little sceptical about her pronouncements in this area, so I was delighted when discovered she was right.

Well, almost.

Like so many flowers, each bluebell has both male and female parts. They are little hermaphrodites, with a central style(female) surrounded by anthers (male).
The style, as you would expect from its name, looks like a post in the middle of the flower.
You don’t really notice the anthers. They are tucked right down in the bottom of the cup, and perform their pollen producing role before the flower opens. (You may be able to see them if you click on this photo to enlarge it.)
As the style grows in the unopened bud, it passes the anthers. It collects pollen on the way, with its purpose-designed hairs. When the flower opens, the style does the job that is done in most other flowers by the anthers, presenting the pollen in a conspicuous position for pick-up by the insect courier service.  (The insects also pick up their "pay", in the form of a bit of nectar). The photo below shows a bluebell in the male phase, well loaded with pollen.

Once the pollen has aged to the point of being unviable, the style moves into the female phase. It splits into three and exposes the sticky surface of the stigma.

Another flush of nectar brings the insects back. If they are carrying pollen from male-phase flower, some adheres to the stigma. From there it makes its way down into the ovary, to grow into seed.

This sex change process is fairly usual in hermaphroditic flowers. They have both male and female parts, but do the jobs one at a time to ensure the spread of their genes around their species. Some, like bluebells, are protandrous - meaning that they are male first, becoming female after that. Flowers that do it the other way round, being female first, are protogynous.

I wish I could tell you which species these bluebells are, but Wahlenbergia ID drives me to despair.
If anyone out there has some helpful tips on how to tell one Darling Downs bluebell species from another, I’d love to hear it.