Thursday, April 25, 2013

Darling Downs Grasslands

I recently found a really excellent blog article on the grasslands of the Darling Downs, written by a visitor from Victoria,  John Morgan, who leads the Plant Ecology Lab at the Department of Botany at La Trobe University.He speaks of "C3" and "C4" grasses.  See article below for an explanation of these terms.
My only criticism of the article is that I wish he had learned to spell the name of our fair city. (It features as "Tawoomba").
(It's an interesting perception, too, that he thinks our local botanists are "more like cowboys". One hopes this is a reference to their sensible headgear, not to their style of botany!)
See it at:

Slender Bamboo Grass, Austrostipa verticillata, a C3 grass

Grasses for All Seasons
C3 or C4?
The first grasses, like most other plants, used a type of photosynthesis known as “C3". Many of them still do. These grasses are known as winter grasses, and tend to be found in the southern half of Australia. Their seeds germinate in autumn, and the plants do most of their growing in autumn and spring. C3 grasses stay green over winter and are at their best in partially shaded areas. They flower in spring, and seeds mature in early summer, after which the plants brown off and remain dormant through the hot period. Then they return to their active growth phase in autumn.
River Tussock Poa labillardieri, a C3 grass

Summer  grasses were a later arrival on the evolutionary scene. They came with an innovation in photosynthesis, known as “C4", which makes particularly efficient use of atmospheric carbon dioxide. They are thought to have evolved around 30 million years ago at a time when the world temperature dropped dramatically, and the available CO2 halved. The C4 process allows these plants to photosynthesise while keeping the pores in their leaves closed. This saves water, but works best in hot conditions. Their ability to make efficient use of water means that they make more green leaf out of a given amount of water than C3 grasses do.

Queensland Blue Grass (Silky Blue Grass) Dichanthium sericeum, a C4 grass.
C4 grasses evolved in the tropics, and their descendants are still happiest in the northern parts of Australia, where the rains come in summer. Their  seeds germinate best in hot, wet weather. Typically fast-growing plants, they are more active in summer than winter, and they prefer to grow in full sun.
Once established, (as indicated by their first flowering), they are very drought hardy. After growing and flowering actively throughout the summer, they have a little rest period in winter, and may brown off.
C4 grasses also tend to be well-adapted to poorer soil..

 Barb wire grass Cymbopogon refractus, a C4 grass
We live in the part of Australia where C3 and C4 grasses overlap. Those of us who like to grow grasses in our gardens have plenty of local native species of both types to choose from. This is a great convenience for gardening, because a mixture allows us to have actively growing green grass for most of the year.
It also means that we can have the beauty of their flowers and seedheads – and the bird-attracting seeds – for a longer period than we would if we only grew one kind or the other.

Choosing Local Grasses for Local Gardens
Here is a shortlist of the more popular perennial grasses for garden use:

C3 Grasses
Austrodanthonia bipartita (Rytidosperma bipartitum) LEAFY WALLABY GRASS
Austrodanthonia racemosa (Rytidosperma racemosum) CLUSTERED WALLABY GRASS
Austrodanthonia tenuior (Rytidosperma tenuius) PURPLISH WALLABY GRASS
Austrostipa aristiglumis PLUMP SPEARGRASS (PLAINS GRASS)
Austrostipa ramosissima STOUT BAMBOO GRASS
Austrostipa verticillata SLENDER BAMBOO GRASS
Elymus scaber WHEAT GRASS
Microlaena stipoides WEEPING RICE-GRASS
Notodanthonia longifolia (Rytidosperma longifolium) LONG-LEAF WALLABY GRASS
Poa labillardieri RIVER TUSSOCK
Poa sieberiana SNOW GRASS

C4 Grasses
Bothriochloa bladhii FOREST BLUEGRASS
Bothriochloa erianthoides (Sorghum erianthoides) SATIN TOP
Capillipedium spicigerum SCENTED TOP
Chloris truncata WINDMILL GRASS
Chloris ventricosa TALL WINDMILL GRASS
Cymbopogon refractus BARB WIRE GRASS
Dichanthium sericium QUEENSLAND BLUE GRASS
Dichanthium queenslandicum KING BLUEGRASS  NB: listed as VULNERABLE
Panicum decompositum NATIVE MILLET
Panicum queenslandicum,  YABILA GRASS (Umbrella grass)
Sarga leiocladum (Sorghum leiocladum) NATIVE SORGHUM
Themeda avenacea NATIVE OAT GRASS
Themeda triandra  (Themeda australis) KANGAROO GRASS

Kangaroo Grass Themeda Triandra


Vanessa said...

Hi Patricia
I'm hoping to plant more native grasses in my garden, and at the moment have a "hedge" of the old purple fountain grass hiding a concrete wall. Is there any of the native grasses that grow particularly tall that I could replace the fountain grass with?


Patricia Gardner said...

Hi Vanessa.
The Austrostipa species are tall. I have written a couple of articles about them on this blog, which you'll find by searching in the white search box on the top left-hand side of the page.
There is also a native fountain grass called Pennisetum alopecuroides. I have also written an article about it, but used its other name "swamp foxtail".