Grasses & forbs

The herbaceous native plants of grasslands are my greatest ecological interest.  To be able to restore a degraded native pasture to wildflower glory is my holy grail.

Bud-banks: the secret of success in a land where the living is not easy –  the secret for a life lived in adversity
Early Nancies – the incomprehensible sex life of this diminutive wildflower.
The autumn colours of grass – who needs deciduous trees?

Bud-banks: the secret of success in a land where the living is not easy
August 2018

When the frosts of winter combine with the added insult of drought, living in the bush on the southern tablelands can be a dispiriting time. This is especially the case when one considers the ground layer vegetation. The summer-growing grasses shrivel to grey, the ground cover is nibbled to an ever more ground-hugging profile, and there are no flowers to speak of.

This dreary, relatively lifeless prospect can persist for years, but as soon as the soil profile is wetted up again the wildflowers spring forth, their splashes of bright colour reminding us once again why we love living in this muted, but beautiful landscape

It’s seeds” – you might think. Everybody knows that seeds can lie dormant in the soil for years, waiting for the right conditions to bring plant life back to the surface. But native plants have been around a long time and seem to have concluded that relying on seeds is not the most successful strategy for undisturbed, nutrient-poor soils in a land where drought prevails much of the time. Instead they bank on a supply of dormant buds and a store of food.

The natives have voted with their roots, so to speak. While they may produce some seed, they mainly invest in deep roots and food storage. Substantial amounts of food may be stowed away in corms, tubers or rhizomes.

Of the 180-odd species of native herbaceous plants that live at Gang Gang, only 27 (15%) are annuals that rely entirely on seeds to grow from year to year. The great majority are perennials that are capable of surviving the hard times by going dormant. This involves withdrawing nutrients and sugars from the leaves to the storage organs. The leaves shrivel up and the plant shuts down until conditions suitable for growth return, and dormant buds reactivate.

While brooding under the ground, the plants have various means of protecting themselves from drying out and they use a small amount of energy to stay alive. The amount of energy used, and the amount stored, determines how long they can stay dormant. In the case of orchids, this can be for years.

Above: Over 70% of the exotic plants on Gang Gang are annuals. The entire plant dies after the seeds mature and seeds are the only means of regeneration. Note the lack of investment in root mass vs the shoots.

Above:  These native Yam Daisies have diverted all the energy collected during the winter to the fleshy underground ‘yams’. Note the shrivelled leaves. The well-provisioned summer-dormant buds will reshoot if there is moisture around next autumn.

The main difference between the two life histories is that germinated seedlings are reliant on sustained moist conditions to establish and have only one shot at adulthood. A Yam Daisy can put out some tentative leaves, replenish the stores as much as possible, but close down shop again if things go bad. Obviously both strategies have their advantages, but the proportion of perennials among Australian native herbs attests to an evolutionary history of low nutrients and stressful growing conditions. The exotic annuals are the new kids on the block, adapted to more nutrients and more disturbance. No one knows which strategy will result in greater success when faced with the combined effects of global warming and land use change. Only time will tell.

Early Nancies – October 2014

I know that I go on about Early Nancies, the harbingers of spring and all that, but it really has been the most brilliant season for this wonderful wildflower, I can’t help but write about them again. A small lily, it has only two leaves and its single flower spike emerges in early September.  It likes a short grass lawn, and grows through winter.  Clearly the good autumn winter rains this year have favoured it.  I can barely put a foot down on our front lawn without treading on one.

The only ugly thing about Early Nancies is their latin name – Wurmbea dioica – I am not even going to try and give you pronunciation tips, because I actually don’t have any.

I was a post-graduate in the 1980s when our lab was visited by an English botanist from Canada. Spencer Barrett did research on rice weeds (my topic of study) but also had an interest in the evolution of plant reproductive systems.  It was Spencer who drew my attention to the mysteries of the Early Nancy, as he had come out to Australia specifically to observe their flowers.

Most plants have flowers that are bisexual, with both female ovaries and male anthers together on the one flower.  However, about 6% of plant species have flowers of different sexes – male flowers with pollen-bearing anthers, and females flowers with ovaries (which set seed once pollinated).  It was a source of great interest to Spencer as to why, and how, this separation of male and female flowers evolved.  And it turns out that while Early Nancies have flowers of separate sex, they can also have in-between states.  In some places, there are three types of flower spikes: all male, all female, and ones with bisexual flowers at the base plus males on top.

The dioecious Early Nancy. On the left, the dark bulging ovaries can be seen on the female flowers, and the dark bands indicating to insects where the nectar is located.
On the right, the ovaries are barely visible and there are anthers bearing pollen. The nectar markers are much paler. These differences are easily seen with the naked eye.

By observing how the gender ratios of the flowers vary in different habitats, clues can be gained as to how and why dioecy (the separation into male and female plants) might have evolved.  Apparently Early Nancies provide a case study worth crossing the globe to pursue, and it turns out that dioecy may confer an evolutionary advantage in dry, infertile habitats.

Since his days crouched over early Nancies in the foothills of the Brindabella Ranges, Spencer Barrett has gone on to a brilliant and distinguished scientific career on the evolution of plant reproductive systems. He has supervised students in their study of Early Nancies, and is an author of many of the 40+ research papers that discuss the wonders of their reproductive system – although the wonders are admittedly somewhat buried in terminology and hard to distil.

These days, I email Spencer twice a year – first on his birthday, which is the same date as mine and therefore easy to remember. And second, in Nancy season, when I take the opportunity to send a photo that shows off our fabulous annual display of his celebrity flower.

The autumn colours of ….. grass? – July 2014

Autumn colour is a great source of fascination to the human race.  Tourist industries are built upon this particular obsession, particularly in parts of North America, although in cooler parts of Australia attempts are also made to cash in on this interest in the colour of dying leaves.  Canberra and Bright (Victoria) are notable amongst them.

Most of us realize that leaves are green because they contain chlorophyll, and chlorophyll uses sunlight, water and carbon dioxide to make carbohydrates.  That is why plants are called primary producers, they make food from scratch (or a least water and air).  Almost every other life-form depends on this photosynthesis to produce the carbohydrates so vital for life.

When winter approaches and it’s getting too cold and dark to photosynthesize efficiently, deciduous plants stop making the green pigment called chlorophyll.  They do this by gradually choking off the supply of nutrients and water to the leaves through accumulation of cork cells in the base of the leaf stalks.  When the plug of cork is complete the leaf eventually falls.

The progressive decay of the chlorophyll reveals orange, yellow and brown pigments that are already in the leaves, but are hidden in summer by green.  As the tree continues to drain the nutrients, the leaves start making red pigments known as anthocyanins.  The red colour that people love so much appears to be largely a by-product of the leaf shutting down, and its use to trees is not well understood.  Sunny autumn days without frost make the reddest leaves.

The problem with deciduous trees is that you have to live with lifeless sticks for the rest of winter.  It’s a bit like the delayed gratification test they do on kids to determine their emotional intelligence  – one marshmallow now or two marshmallows later?  An immediate blaze of colour now, or soothing green foliage to enjoy all winter?

Having grown up literally in the canopy of an elm forest, you’d think I might have some affinity with deciduous trees, but no, I prefer the year-round green foliage of the eucalypt over an autumn dump of yellow leaves.  The yard maintenance was too off-putting for a teenager – leaves in the gutters, on the paths and my parents even installed a swimming pool in the elm forest.

Nowadays I get my autumn pleasure from grass.  Showing a friend our native grassland on Gang Gang a while ago, I was impressed when she pointed out the glorious autumn colours of the grasses as they approached dormancy.  It is now a highlight of the year.

My current computer wallpaper is a kaleidoscope of mellowing green blending into golden yellows giving ways to intense oranges and delicate pinks.  These are the colours of an autumn perennial grassland glowing in the midday autumn sun.  Because the native grasses are predominantly summer-growing species, they shut down in the cooling temperatures and shortening days in much the same way as deciduous trees.  Their colours can be quite intense, but in this photo they are a magical balance of gentle pastels glowing intensely in the light.

Sadly, these glowing pigments too will break down in the same way as autumn leaves, except the grass leaves remain attached to the plant.  Over winter they will fade to brown and then grey, becoming increasingly bleached as they make their way to being eventually organic matter in the soil or fuel for a fire.  So if you have any remnants of autumn colour in your native grasses, enjoy them now, as while the mild spring has delayed the autumn, they will be fading before your eyes.

Interestingly, it is the winter-growing introduced pasture grasses and weeds that provide the soothing greens over winter – providing the frosts don’t fell them and rainfall permits their growth.  Gang Gang in August would be grey and somewhat depressing if it were not for the cheery flowering wattles and the promising buds of the yam daisies.