Some posters

For people with children, these high-resolution posters are intended for printing on A3 paper, and can be freely downloaded:

Mathematics posters: Flat shapes, Solid Shapes, Prime Factors (colour-coded)

Biology posters: Ladybirds of Australia, Plants and Fungi, Some Flowering Plants (monocots marked with a dot)

Astronomy/geography posters: Southern Cross (showing colours and magnitudes of stars), Orion (ditto), Geographical Features

Technology posters: Vehicles, Milestones in Materials

Australian plant families revisited

This visualisation (revising an older post) shows the sizes of major Australian plant families, compared to world totals (based on slightly old data from here).

Australia’s 836 orchid species are only 3% of the world total, but Australia has 89% of the Goodeniaceae.

Plants illustrated include the Golden Wattle and Sturt’s Desert Pea.

Joseph Dalton Hooker

The botanist Joseph Dalton Hooker was born 200 years ago, on 30 June 1817. Kew Gardens, of which he was the director, has a special event to commemorate him. Hooker travelled on expeditions to Antarctica, India, Palestine, Morocco, and the Western United States. The pictures below are from his The botany of the Antarctic voyage of H.M. discovery ships Erebus and Terror in the years 1839–1843, under the command of Captain Sir James Clark Ross. He also published several volumes on the botany of India.

The Acacia wars, resolved

In an at times acrimonious process (some have even called it a “wattle war”), the former plant genus Acacia has been split into five genera, with further splits likely. The XVIII International Botanical Congress in 2011 confirmed a previous decision to retain the Acacia name for the largest of the resulting genera, found mainly in Australia:

“Under the internationally accepted rules governing the correct naming of plants, the International Code of Botanical Nomenclature, the name would normally have remained with the African-American group, as this includes the species Acacia nilotica, which is the nomenclatural type species… However, a special provision of the Code allows for the name of the type species of a genus to be changed in cases like this, where strict application of the rules would require a large number of species to be renamed… An application under this provision was made in 2003… This was considered by the relevant botanical committees, who decided in its favour. The International Botanical Congress at Vienna in 2005 ratified this decision. The Vienna decision was contested by a group of botanists involved with African and American acacias. The Melbourne Congress, in two important votes on the first day of the Nomenclature Section, supported the procedure used in Vienna by a large majority. Support for this decision was widespread and not confined to Australian delegates. This vote effectively confirmed that the type species of Acacia is now an Australian species.”

The resulting division of the former Acacia is as follows:

The map below shows the distribution of the new genera, divided into the Americas, Africa, Asia, and Australia & the Pacific (background image from NASA Visible Earth). A degree of reorganisation was going to be needed whatever nomenclature proposal was accepted, but it certainly made sense to retain the Acacia name for 71% of the original species (although Wikipedia, which becomes more and more partisan as time passes, ran a campaign against the official decision for several years). The botanical community seems quite happy using the new names, and it does not seem that the issue will resurface at the XIX International Botanical Congress later this year, although there continues to be debate about how to resolve similar issues in the future.

Here are the five new genera, with examples:


About 13 species, in the Americas. See

Mariosousa willardiana (Palo Blanco – photo: Tomas Castelazo)


About 15 species, in the Americas. See

Acaciella angustissima (photo: USDA)


About 163 species, throughout the tropics. See

Vachellia smallii (photo: Stan Shebs)


About 203 species, throughout the tropics. See This genus is likely to be split further.

Senegalia laeta (photo: Marco Schmidt)


About 987 species, almost all in Australia and the Pacific.

Acacia pycnantha (Golden Wattle – photo: Melburnian)

A Wellcome donation

The Wellcome Library has donated to Wikimedia Commons over 100,000 images relating to medical history, rare books, Asian art, and other topics. The images are available from (progressively) or from under a Creative Commons Attribution only CC BY 4.0 licence (giving credit to ‘Wellcome Library, London’). Example images from this treasure trove include:

Blow fly (Chrysomya chloropyga) – coloured drawing by Amedeo John Engel Terzi

Hebrew manuscript

Indian game of Snakes and Ladders

17th century Japanese herbal

Arabidopsis thaliana: a model plant

Arabidopsis thaliana, the thale cress (photo above by Peggy Greb, picture below by Johann Georg Sturm and Jacob Sturm, 1796) is a small flowering plant in the family Brassicaceae – the mustard/cabbage family.

During much of the 20th century, A. thaliana was the target of extensive research, facilitated by the small size of the plant (and of its genome), its short life cycle, and its suitability for light microscopy. Sequencing of the genome was completed in the year 2000, and the genome is available at The open-access peer-reviewed The Arabidopsis Book also collates information on the plant, which is in many ways the botanical equivalent of Caenorhabditis elegans. It has taught the world a great deal.

The Google Ngram below shows the explosion in Arabidopsis-related literature since about 1990, outstripping even work on C. elegans:

Three lovely scanning electron microscope (SEM) images

A wonderful image of pollen from sunflower, morning glory, hollyhock, lily, primrose, and castor bean plants (Dartmouth Electron Microscope Facility 2011, colourised by William Crochot).

Image of a strawberry by Annie Cavanagh and David McCarthy of the School of Pharmacy, University of London. This beautifully detailed image was created in 2010 by stitching several different SEM images together. I have mentioned this image before. It comes via via Wellcome Images, and more of the story is here.

A human human T-lymphocyte (white blood cell), colourised blue (NIAID 2010).

Sydney Parkinson and Joseph Banks

Joseph Banks was the botanist who accompanied Captain Cook on his 1768–1771 voyage to Australia and the South Pacific. The genus Banksia is named in his honour – the Banksia integrifolia above is one example of the genus, and is taken from Banks’ botanical work, the Florilegium, which is partially available online at the Natural History Museum in London.

The artwork in this book is largely thanks to Sydney Parkinson, the artist who accompanied Banks (his self-portrait is below). Working under difficult conditions, Parkinson produced 943 botanical drawings (including 269 finished watercolours), but died of fever on the voyage back from Australia (he was only 25). A number of artists in England completed what this young hero of botany had begun, allowing the rest of the world to experience some of Australia’s unique and bizarre flora. Thank you, Sydney.

Kitchen chemistry: Ethylene and ripening fruit

My previous kitchen chemistry post discussed the combustion of propane. Propane is a hydrocarbon – propane molecules are made up only out of carbon and hydrogen atoms.

Another hydrocarbon gas that can be found in the kitchen is ethylene (ethene). Ethylene molecules consist of two carbon atoms and four hydrogen atoms (with a double bond between the carbon atoms, so that each carbon atom still has four connections). Here are two views of an ethylene molecule:


Like propane, ethylene burns (C2H4 + 3 O2 → 2 CO2 + 2 H2O). Ethylene molecules can also be combined together to give the plastic polyethylene (polythene).

Perhaps the most important function of ethylene in the kitchen, however, is that it is produced by ripening fruit (as was discovered in the 1930s). What’s more, ethylene gas causes other fruit (particularly apples, pears, and bananas) to become first ripe, and then over-ripe. As the saying goes, “one bad apple spoils the whole bunch,” because the ethylene gas produced by one ripe, over-ripe, or damaged apple affects all the others in the barrel (see this home experiment on the subject). Vegetables are affected as well. To stop this from happening, packets of ethylene-absorbing material can be placed in the refrigerator.