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Common name:     Grasses                                           

Etymology of scientific name:   From the Ancient Greek πόα (póa, "fodder")

Flowers:                  

• Inflorecence scheme and floral diagram. 1 – glume, 2 – lemma, 3 – awn, 4 – palea, 5 – lodicules, 6 – stamens, 7 – ovary, 8 – styles.

• With around 780 genera and around 12,000 species, the Poaceae is the fifth-largest plant family, following the Asteraceae, Orchidaceae, Fabaceae and Rubiaceae.

• The Poaceae are the most economically important plant family, providing staple foods from domesticated cereal crops such as maize, wheat, rice, barley, and millet as well as feed for meat-producing animals. They provide, through direct human consumption, just over one-half (51%) of all dietary energy; rice provides 20%, wheat supplies 20%, maize (corn) 5.5%, and other grains 6%. Some members of the Poaceae are used as building materials (bamboo, thatch, and straw); others can provide a source of biofuel, primarily via the conversion of maize to ethanol.

• Grasses have stems that are hollow except at the nodes and narrow alternate leaves borne in two ranks. The lower part of each leaf encloses the stem, forming a leaf-sheath. The leaf grows from the base of the blade, an adaptation allowing it to cope with frequent grazing.

• Grasslands such as savannah and prairie where grasses are dominant are estimated to constitute 40.5% of the land area of the Earth, excluding Greenland and Antarctica. Grasses are also an important part of the vegetation in many other habitats, including wetlands, forests and tundra.

• Though they are commonly called "grasses", groups such as the seagrasses, rushes and sedges fall outside this family. The rushes and sedges are related to the Poaceae, being members of the order Poales, but the seagrasses are members of order Alismatales. However, all of them belong to the monocot group of plants.

Fruit:                         

• x

Leaves:         

•     x   

Habit:        

• Poaceae (/poʊˈeɪsiaɪ/) or Gramineae (/ɡrəˈmɪniaɪ/) is a large and nearly ubiquitous family of monocotyledonous flowering plants commonly known as grasses. 

• It includes the cereal grasses, bamboos and the grasses of natural grassland and species cultivated in lawns and pasture. The latter are commonly referred to collectively as grass.

Habitat:                     

•    x

Species:                     

• World:            12 000 S,    780 G

• Australia:      S,    G

Additional notes:                 

• Grasses may be annual or perennial herbs,[17]: 10  generally with the following characteristics (the image gallery can be used for reference): The stems of grasses, called culms, are usually cylindrical (more rarely flattened, but not 3-angled) and are hollow, plugged at the nodes, where the leaves are attached.[17][18] Grass leaves are nearly always alternate and distichous (in one plane), and have parallel veins.[17]: 11  Each leaf is differentiated into a lower sheath hugging the stem and a blade with entire (i.e., smooth) margins.[17]: 11  The leaf blades of many grasses are hardened with silica phytoliths, which discourage grazing animals; some, such as sword grass, are sharp enough to cut human skin. A membranous appendage or fringe of hairs called the ligule lies at the junction between sheath and blade, preventing water or insects from penetrating into the sheath.[17]: 11 

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• Flowers of Poaceae are characteristically arranged in spikelets, each having one or more florets.[17]: 12  The spikelets are further grouped into panicles or spikes. The part of the spikelet that bears the florets is called the rachilla. A spikelet consists of two (or sometimes fewer) bracts at the base, called glumes, followed by one or more florets.[17]: 13  A floret consists of the flower surrounded by two bracts, one external—the lemma—and one internal—the palea. The flowers are usually hermaphroditic—maize being an important exception—and mainly anemophilous or wind-pollinated, although insects occasionally play a role.[19] The perianth is reduced to two scales, called lodicules,[17]: 11  that expand and contract to spread the lemma and palea; these are generally interpreted to be modified sepals. The fruit of grasses is a caryopsis, in which the seed coat is fused to the fruit wall.[17]: 16  A tiller is a leafy shoot other than the first shoot produced from the seed       

• Grasses include some of the most versatile plant life-forms. They became widespread toward the end of the Cretaceous period, and fossilized dinosaur dung (coprolites) have been found containing phytoliths of a variety that include grasses that are related to modern rice and bamboo.[9] Grasses have adapted to conditions in lush rain forests, dry deserts, cold mountains and even intertidal habitats, and are currently the most widespread plant type; grass is a valuable source of food and energy for all sorts of wildlife.    

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The rise of grasses and grasslands in Australia     (http://morganvegdynamics.blogspot.com/2015/10/the-rise-of-grasses-and-grasslands-in.html) 

Recently I've been thinking about my favourite biome - the grasslands - and when they came to prominence in Australia. Was it because of megafauna? Was it because of climate? Was it because of Aboriginal burning?  So, I started reviewing the literature and thought I'd share my findings here. It's a fascinating topic and one that I'm pretty sure most biologists / grassland aficionados  /ecologists aren't entirely familiar with.

While tussock grasslands are a widespread vegetation type in Australia, grassland ecosystems per se were largely absent from Australia until fairly recently. It is also likely that the C4 contingent of grasses that currently occur in Australia are recent arrivals to the continent. Jacobs et al. (1999) provide a comprehensive review of the topic. 

Grasses originated in Gondwana during the Cretaceous (>65 million years ago (Ma)) with some speculation that graminoids possibly originated in East Gondwana, notably the area that later became Australia. In Australia, however, there are almost no early preserved grass macro-fossils, possibly due to the bias towards their preservation in wet environments. The earliest record of Australian grass pollen is from the mid Eocene (~45 Ma), but it has always been relatively sparse in the Australian fossil record, only becoming most abundant within the last 2 million years.

Grass pollen first occurs in north-western Australia, possibly forming savannah by the mid-Miocene (~15 Ma). The expansion of open vegetation types accelerated in the late Miocene due to increased climate seasonality. There were rapid evolutionary radiations in many large Australian groups such as the sclerophyll taxa Eucalyptus, Banksia and Allocasuarina at this time, as well as grasses. Austrostipa, for example, originated and began to diversify between 25 and 10 Ma, and a rapid radiation occurred, indicated by a high diversification rate at that time. Increasing taxonomic diversity may have resulted from adaptation to newly derived arid niches caused by climatic changes.

From north-west Australia, grasses expanded south-east through central Australia as aridity intensified through the Late Tertiary. Grasses were present in northern and central Australia, extending into the Murray Basin, in the early to mid Miocene. The entry of grasses into more southern and eastern areas of Australia occurred in the mid to late Miocene and early Pliocene (~5 Ma). Fires were part of the landscape in the Murray Darling throughout the Miocene, increasing with climate seasonality, potentially facilitating the spread of grasses and grasslands, particularly those dominated by C4 grasses.

Themeda triandra - one of the most widespread

C4 grasses in Australia

Many grasses that are now common in Australia appear to have migrated from Asia during the Miocene when Sundaland (the Indonesian archipelago) collided with the Australian plate, including the C4 genera Themeda, Dichantheum and Bothriochloa. A number of tropical south-east Asian genera have strong representation in Australia due to this early migration. All are tropical grasses which extend into the temperate zone of southern Australia. The Andropogoneae (which includes all the above genera) have major centres of distribution in south-eastern Indonesia and India, with a lesser centre in central eastern Africa. This infers that the taxa have entered Australia from the north since its collision with Asia (although Andropogoneae may have existed in Australia before this time). It is likely that Themeda migrated from south-east Asia into both South Africa and Australia in the late Tertiary; it is now widespread in both continents.

C4 grasses extended into the temperate regions of the south of Australia, most notably, Themeda, the genera that subsequently became the dominant mesic grassland type in the south-east of the continent. In southern Australia, however, grasses did not achieve their current prominence until the Late Pleistocene. Explanations for the C4 expansion across the landscape in the Miocene have invoked changes in the seasonality of climate, particularly climate drying, given the C4 pathway appears to give grasses a competitive advantage in arid environments, and to changes in fire regimes. Increases in the abundance of the major C4 clades Paniceae and Andropogoneae were thought most favoured by these changed conditions, although the reasons for the rise of C4 grasslands per se are still debated. New research, for instance, suggests that the C3 Pooideae (which include the Stipeae) expanded into cooler climates rather than being outcompeted by C4 grasses, an event that is possibly as important as the global C4 expansion.

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