Tuesday, 26 July 2016

Australia's Black Wattles a flight hazard in China


Australia's Black Wattle may soon become a problem for planes flying through China. Not because the trees will grow tall enough to interfere with flight paths, but because they rather like growing in airports and birds like to roost in them.

We grow Black Wattle (Acacia mearnsii; not the unrelated Callicoma serratifolia which New South Welshman tend to call Black Wattle) in the Australian Garden at Cranbourne Gardens (above) as a quick growing screen for other plantings - in this case, with other wattles, in the Gondwana Garden.

Scientists in China, however, are worried that our Black Wattle is spreading so quickly through open landscapes such as those surrounding runways, that it may soon be a problem for aviation and local biodiversity. The airports are in Yunnan Province, in the southwest of China, including the Kunming Changshui International Airport (below, by Min Liu) where many Australian botanists and plant collectors have arrived to help document and bring into propagation Chinese plants.


Wattles have been planted deliberately in many countries to to improve soil (like most legumes, wattles bringing with it bacterial nodules that fix nitrogen and make it available for other plants and organisms), and for timber, adhesive and tannin production. 

The bark of Black Wattle contains a chemical useful for tanning leather and has been grown for this purpose in places such as Brazil, China and many South African countries. In fact the extracted tannin is exported back to Australia.


That's all good but the Black Wattle is also in the top 100 of the world's worst invasive alien species. The seeds are notoriously long-lived, and spread by rodents and birds, and often locals moving the plant around for firewood. Black Wattle is fast growing, 'fixes' its own nitrogen, doesn't mind a bit of salt in the soil and likes growing in disturbed areas.

The native (largely non-human assisted) range of Black Wattle is southern Australia - from around Hobart through to half way up the New South Wales coast - and its human assisted range now extends to Western Australia, North America, South America, Asia, Europe, Pacific Islands, Africa and Europe. In fact, as Neville Walsh reminded me (based on his memory of a discussion with Jim Ross, ex-South African and ex-Chief Botanist at Royal Botanic Gardens Victoria), the species was named after an American collector, Edgar Mearns, who found the plant growing in Kenya and other parts of East Africa in 1909.


Time for a breather. To refocus at a finer scale for a moment, if you are trying to separate Black Wattle (top picture above) from Silver Wattle (Acacia dealbata; bottom picture) look closely at the fern-like leaves. Black Wattle has green rather than silvery leaves - it is sometimes called, helpfully, the Green Wattle.

Black Wattle also has a different arrangement of raised 'glands' (the pimples with dots in the pictures above). You find them at or near the feathery leaf junctions as well as in between some of them. Be careful though. The number of in-between glands is variable, and sometimes there are none. Helpfully though compared to the Silver Wattle the glands in Black Wattle tend to not line up as well with the feathery off-shoots.


Now, back to China. It isn't so much that the Black Wattle will grow close enough to the runway to irritate pilots on take off and landing, although that must be one concern. The main problem, it seems, is an increase in 'bird strikes' (i.e. birds getting sucked into bits of a plane where we'd rather they didn't) due to more roosting places

How this wattle managed to become a flight hazard in Kunming is explained deeper in the paper. Prior to 2007, the airport was reclaimed land, once used for villages, farmland and planted forests. The latter included Black Wattle as a planted species and it's assumed there are extensive seed banks of the species in the soil. 

The climate around Kunming is very similar to southern Australia, which is why botanic gardens such as those of Sydney and Melbourne have sent expeditions to this area to collect suitable garden plants such as camellia species. 

Finally, plane movements themselves can move seeds around the airport land and then when new buildings or runaways are constructed, such activities break the dormancy of the seed. 

So all up this is another example of how by manipulating nature we can inadvertently cause ourselves a heap of problems. That's putting aside the local plants and animals that might be displaced. However with Fred Pearce's voice still reverberating in my head, I should note that at least 34 Chinese bird species live in and near the Black Wattle and may well thrive in its presence. That's if they stay clear of passing jet engines.

Images: all pictures other than at Kunming airport and the close of a Silver Wattle leaf (from near the Yarra River at Hawthorn) are from the Australian Garden, Cranbourne Gardens, part of the Royal Botanic Gardens Victoria.

Tuesday, 19 July 2016

A wild and toxic tomato


The Bush or Wild Tomato is a thorny and toxic thing, growing in seasonally inundated areas of otherwise mostly arid Australia. It grows naturally in every mainland State of Australia except Victoria, where it grows 'unnaturally' (having become established as a weed near Dimboola, presumably as a result of human activities).

Solanum quadriloculatum is one of 32 species of Solanum in Victoria, 185 more or less in Australia and something like 1500 worldwide. So Solanum is a big genus, mostly in tropical and subtropical America but also well represented in Australia and Africa. As with my last few plant posts, you can see the subject doing nicely in the Australian Garden at Cranbourne Gardens.

Its family Solonaceae is fully of lovely edible plants such as the garden tomato and potato, and some particularly toxic plants such as Deadly Nightshade (Atropa belladonna). Solanum itself is similar. Our species, Solanum quadriloculatum has been described as 'DEADLY' and 'NOT edible' for humans, and appears to be toxic to cattle. This is despite it carrying the evocative common name of Bush Tomato.

There are native tomatoes in the bush (such as Solanum ellipticum, and another eight species in central Australia) whose fruit you can eat, some after removing the seed and then drying or roasting, but best not to eat any wild tomato unless you have expert botanical and culinary advice on hand.


The Bush Tomato, Solanum quadriloculatum, has, and the species name suggests, fruits with four segments (locules). The angular fruits are also distinctly 'spongy when green, hard when ripe'. Very hard it seems - like bone! But then so are some other, edible, native species of Solanum.

The leaves are woolly with star-shaped white hairs, punctuated in places by long purplish-black spines or prickles. The prickles bristle around the stems but peter out on the leaves where you find them scattered along the veins but not in between.

I'm reluctant to even indirectly promote a website that promotes homeopathy*, but I am amused by the 'flower essence' of this species being described as giving a 'sense of being weighed down and encumbered' (negative) or providing 'freedom to move on in life' (positive). I guess dying from eating its poisonous fruits would be an encumbrance, but surviving would allow you to at least move on.

Here are a few more images I took a few weeks ago of the soft, and not so soft, indumentum, which I find captivating. More than enough to keep living, with a light heart.


*I'm advised that the 'bush flower essences' sold by Newton's are not marketed as homeopathic (they are considered herbal or naturopathic).

Tuesday, 12 July 2016

Brained agents discover gambling peas


"We do not conclude that plants are intelligent in the sense used for humans or other animals, but rather that complex and interesting behaviours can theoretically be predicted as biological adaptations ... [T]he findings lead us to look even at pea plants as dynamic strategists and to model their decision processes just as one would model an intelligent agent."

So says Professor Alex Kacelnik, from the Department of Zoology at Oxford University, elaborating on the results in his co-authored paper in Current Biology. Enter the pea plant as a strategist and in this case one prone to gamble for its longer term benefit.

A zoologist is of course is unlikely to ever think of a plant as intelligent as an animal, even though in recent years philosophers and botanists have strayed into this territory, but a gambling pea has raised the stakes.


This group of researchers from the UK and Israel showed that a pea plant could in effect take a risk on where it produced roots if it somehow assessed that would be on balance a good thing for its survival. Laboratory plants had their roots split between two pots, one with a constant level of nutrients, the other with varying levels. If the nutrient levels in the constant pot were low the plant took a gamble and produced more roots in the second pot. If nutrient levels were constantly high, it didn't bother.

This is how Current Science illustrates it:


And this is pretty much how we respond to risk. The human example they give is the choice between a guaranteed $800 or tossing a coin to receive $1000 for heads and nothing for tails. Mostly you take the reliable $800, but if you needed $900 for a fare to get home from a remote location and to survive a potentially threatening situation, you may as well take your chances. The $800 doesn't help at all while the toss of a coin gives you a fifty fifty chance of getting out of there.

So these pea plants realised - well, were hard wired to conclude - that if the going was no good in one pot they may as well risk sending roots (and using up valuable resources) by exploring territory that may or may not provide a better source of what they needed to survive. The plant was able to assess that this risky option could help them survive longer.

Presumably the pea plant is 'simply' tempted by the higher nutrients on the occasions when the variable pot is in the positive territory but the interesting thing is that this seems to only happen then the stable pot is low in nutrients. So they aren't tempted by more nutrients when things are reliably sufficient in the other pot. That is, if the peas were us they are happy to take the $800 on offer unless they need more than $800 to survive and their sensors tell them there is what we might call greener grass elsewhere worth investing in.

So don't tell Nick Xenophon and his NXT Party (for non-Australians, this is a political party with one of its central - and very reasonable - tenets that we should do all we can to reduce gambling in Australia, including banning its advertising) but plants seem be we willing and able to take a bet. 

The researchers now want to present plants with all kinds of other tasks to test what they call their 'adaptive responses'. Their goal is to find out just how much a plants evolved responses resemble the way 'brained agents', like us, make decisions. The zoologists are unlikely to be ever convinced that plants are intelligent but we know, don't we...


Images: The pea with a face is the icon used for twitter handle @Just_a_pea, the cartoon from Current Biology, and the others are of plants growing outside our back door at home (just don't tell Lynda I've uprooted one to photograph it for this post).

Tuesday, 5 July 2016

Bloody Australian citrus


This clotted-blood-like fruit is an Australian bred citrus growing in our Australian Garden at Cranbourne Gardens. It's an example of the dozens of new citrus cultivars available now with at least one of their parents a local species (you might have caught Angus Stewart singing their praises on the 25 June episode of Gardening Australia).

When I last posted on citrus I was announcing that a large number of Citrus species are native to our part of the world. That part is Papua New Guinea, New Caledonia and Australia, where you'll find half of the world's 25 species of Citrus. One of those local species is the appropriately named Citrus australasica (the Finger Lime), a parent of this black dimply fruit.

We call it Australian Blood but it's also known as Australian Blood Lime, Australian Red Centre Lime, Australian Red Lime or simply Red Lime. A hybrid between Citrus australasica var. sanguinea ('sanguine' means blood red, a red fruited variant of the Finger Lime) and Citrus x limonia (the Ranpur Lime, a cross between a mandarin and a lemon), it produces a small but striking fruit in late autumn (when I took these photographs).


According to one of its growers, the plant was selected by CSIRO at Merbein in 1990. Like many citrus, the skin colour of the fruit is variable depending on growing conditions and maturity. In this case it can be gold with red markings or fully blood red. The ones I photographed were a little more like congealed blood, or at best a dried burgundy-blood colour. Inside the flesh can be lime-coloured (as these were), or partly or fully red.


It tastes like a lime, with that appealing popping sensation as you crush the 'vescicles' of juice, as in a Finger Lime. Also like the Finger Lime, the bush is a little spiny.

Australian Sunrise is another cultivar we grow in the Australian Garden, and it too has the Finger Lime as a parent, this time the non-red variety. The fruit and plant look very like the Australian Blood and that's because the other partner is the Calamondin which, as I mentioned in my previous post, is a  hybrid between a mandarin and a cumquat (not miles away from the Ranpur Lime).

Australian Sunrise is what the breeders call an 'open-pollinated seedling' from the hybridisation of those two parents, a thing itself called Faustrimedin. Anyways, this one produces fruits with orange or golden skin (as below), and sometimes a second crop each season with duller and greener skins.


In older literature you might see the Australian citrus classified in genera such as Eremocitrus and Microcitrus but these days we include all the citrus-like species in Citrus (although there are still a couple of more distant citrus relatives put in other genera).The Australian Plant Census lists nine species and five formally named hybrids from Australia, including of course Citrus australasica, the common element in the two cultivars I've featured today.

The first Director of Royal Botanic Gardens Victoria (when it was named otherwise), Ferdinand von Mueller, described this species in 1858 from a collection made at Moreton Bay in Queensland. The natural distribution of this species is clustered around Moreton Bay, and Brisbane, where it grows in wet and dry rainforest near the New South Wales/Queensland border. The variety sanguinea was described by Queensland Colonial Botanist, Frederick M. Bailey, in 1892, from Tambourine Mountain. I don't know if it occurs in naturally in any other locations.

Australian species tend to be more drought, salinity and disease tolerant that other species of Citrus and they hybridise relatively freely with many other species and hybrid-species. This makes them ideal candidates as rootstocks, and for grafting onto other successful rootstocks. Those selections with unusual fruit colours, shapes and flesh textures - such as many of the Finger Lime crosses - are becoming ever popular with a market forever it seems in search of something new to eat.

Tuesday, 28 June 2016

Australian nonsmoking plant


Native Tobacco grows in rocky places throughout the eastern two-thirds of New South Wales and all but the north-central chunk of Victoria, in the Arid and Home Gardens at Cranbourne Gardens, and at least temporarily in my front garden at home.

As is the want with this kind of common name, 'native tobacco' only makes sense in the local context and the plant is also sometimes referred to as Australian Tobacco (despite learned publications sometimes using the name Austral Tobacco surely no-one ever says 'Austral' commonly).

Nicotiana suaveolens, as botanists call it, is a lanky annual up to one and a half metres tall, with long tubular white flowers. Another local species, Nicotiana maritima, is similar but is covered in woolly hairs, has generally smaller flowers and never gets more than one metre tall. Although relatively widespread and common in South Australia, Nicotiana maritima has only been confirmed from a few scattered locations in Victoria and may now be extinct.


However ... while the plants photographed here are definitely not woolly, they do have some soft hairs at the base of leaves and around the flowers. It's this trace of hairiness and the difficulty in using things like plant height as a taxonomic character (all plants have to be small at some stage of their life, and may be stunted in conditions are not ideal) that leads some botanists to be a little sceptical of these two being separate species. An overlap in flower size, the other diagnostic character, doesn't help.

Those that know both species better say there is more to it and the flowers may have some further subtle differences. Conservation botanist Neville Walsh is growing up seed of both species at the moment to do a direct comparison. Depending on the outcome of this experiment it may be that we don't actually have, and perhaps never have had, Nicotiana maritima in Victoria, just a bit of variation in Nicotiana suaveolens. 

Either way, the Australan Tobacco is a tobacco plant, but not one that people tend to smoke. Commercial tobacco comes from Nicotiana tabacum or Nicotiana rustica, both from tropical and subtropical America (the former of hybrid origin). Nicotiana tabacum sometimes escapes from cultivation and becomes established in bushland, but it tends not to persist. (These are the opened fruits of Nicotiana suaveolens:)


Since 2006 it has been it has illegal to grow either species, or Nicotiana sylvestris, in your home garden in Australia. This is because such plants are used for 'smoking, chewing or snuff' and therefore considered 'to be tobacco plants for the purposes of the 1901 Excise Act'.

While the Aregentinian species Nicotiana sylvestris is not grown commercially, there appears to be a small trade in it as an ornamental plant and promotion of it as a source of smoking/chewing/snuffing tobacco. It appeared as a weed in central Victoria in the 1960s but has not been recorded since.

Expert advice is that if other species of Nicotiana are developed so their leaves can be used in similar ways then these too would be considered tobacco plants, and should not be grown.

As things stand it seems you can grow Nicotiana suaveolens, but please not ingest it or its vapours in any way.


Images: These photographs were taken in the Growing Friends Nursery at Cranbourne Gardens in early May. 

Tuesday, 21 June 2016

Gourds of two sizes needed for Papuan heath


This rather exotic heath, with flowers and fruits like a pumped-up blueberry, is four years old. It was propagated from a cutting by our nursery horticulturist Dermot Molloy. Until a month or so ago we hadn't confirmed its species name, although we knew it was a Papua New Guinean member of the heath family and, we were pretty sure, in the genus Dimorphanthera.

[Nearby in the nursery we have Macleania ruprestris, in the same family but from Chile, also with chunky bell-like flowers followed by a succulent berry. It's in berry at the moment - pictured to the side here - with some very small flower buds appearing at the branch tips. So with two species, we have the making of a fascinating collection!]

There are (or at least were in 2003) 87 species of Dimorphanthera, most of them native to New Guinea or nearby, a region that might be described as eastern Malesia. They are shrubs, small trees or sometimes lianas, but no matter their life form, they tend to climb or drape themselves over other plants. Those plants include relatives in the heath family Ericaceae, such as Rhododendron and a genus more similar to Dimorphanthera, Vaccinium (including species that gives us cranberries and blueberries).

Now, let's tease one of those flowers apart...


The name 'dimorpho-anthera' refers to the flowers having two different kinds of anthers, the pollen-bearing male bits. Typically half of these almost woody anthers are bigger than the other half. In the flower I pealed open the anthers all looked pretty much the same but they tend to be in pairs with one longer than the other and with the green bit extending beyond the brown strips either double or singly pointed (most obvious in the bottom two in the picture above).

Apparently such an arrangement is an attractive, or at least productive (for the plant), proposition for visiting birds, which seem to be the targeted pollinators. Mostly I suspect they are just curious about what's inside the fleshy, porcelain-coloured tube.


Our first Director, Ferdinand von Mueller, devised and applied the name 'Dimorphanthera' to this group of plants, firstly in 1886 as a subgenus of Agapetes (although not adequately, and a later author, Carl Georg Oscar Drude had to rectify it to meet the needs of botanical nomenclature).


In 1890 (above), Mueller raised Dimorphanthera to genus level in the second volume of his notes on Papuan plants, again rather ineffectively (you see various renderings of the 'authorities' for this name, including Johannes Jacobus Smith as fixing up Mueller's genus name attempt).

So that's the genus. Our horticultural botanist, Roger Spencer, has now confirmed the genus and given it a species name: Dimorphanthera alpina. The shape of the green calyx at the base of the flower, the size of all the floral parts and the colour of the floral tube (the fused petals) all match this species. As do the rather cryptic black spots on the edge of the leaf, which you can (just) see in the following picture (along with an unopened flower bud). Roger confirmed these spots are actually small teeth, slightly embedded into the leaf margin.


To grow Dimorphanthera alpina it seems best to treat it like a Vireya Rhododendron, providing good drainage and protection from extreme cold (frosts). Although from the tropics, as its name suggests it grows at higher altitudes and will tolerate night temperatures down to around 10 degrees C. Like others in the family (e.g. Rhododendron) it likes acidic soils.

Royal Botanic Gardens Edinburgh has an extensive collection of Dimorphanthera, with 19 'taxa' (species, and categories below species like subspecies, varieties and forms) growing in 2012. Elsewhere it's not a widely grown genus. It should be.


Tuesday, 14 June 2016

Xocolatl! Presumed goat droppings make good god food


Sydney's newest botanical attraction, The Calyx, opened on Saturday, starring Theobroma cacao and its popular products. Lindt is a beneficiary of the products (and a sponsor) giving you a hint about what's inside these yellowish fruits.

(If you want to experience the construction of The Calyx in time-lapse, or see it the way a drone does, talk a look at these videos.)

Theobroma is Latin for 'food of the gods' and those gods were or are presumably those of the Aztecs. Native to tropical America, the Cocoa Tree was called Xocolatl by the Aztecs, meaning bitter water. From Xocolatl we get the species name cacao and our own common names for the crushed beans, Cocoa and Chocolate.

Surprisingly, perhaps, Theobroma is in the mallow family, Malvaceae, with things like hibiscus and cotton. Still, you also find tucked into this family odd things like kapok and durian. There are 21 other species of Theobroma, including one with fruits that are juiced in South America. But chocolate is the main reason you are familiar with the genus.


Chocolate can be good for you, as the possum in the nest above will attest. It's said that eating a little a day - 46-105 grams - can help lower blood pressure. The cocoa seeds have also been used to treat various ailments, including heart disease, in humans.


Mostly we eat the dried and fermented seeds of the Cocoa Tree (which we then call cocoa beans) because they taste good. I like mine with just a little sugar: 70% cocoa, in the 'bittersweet' range in the US, is my preference.

About 30 to 40 of these seeds are produced inside a large yellow, to red or orange, fruit (see top of post) that looks like the Beatles' Yellow Submarine or perhaps a pointy egg. Technically it's a berry but generally referred to as a pod.

Before it fruit, the plant flowers. The flowers erupt out of the stem, something you find in a few tropical plants and which we like to call cauliflory.


According to Royal Botanic Gardens Kew, fruits in the wild are pollinated by midges. In our glasshouses - and the pictures above were taken from the Palm House at Kew Gardens as well as the The Calyx in Sydney - hand pollination is needed. Although ants do help out at Kew Gardens, and there is some kind of blurry midge/fly in the bottom right of the first picture!

Dale Dixon, Curator Manager of Royal Botanic Garden Sydney, says they are struggling to get any viable fruit in the Calyx plants. The small success below, on one of their trees, seems to have aborted before full development.


Even in nature it seems a very small percentage (5% says Kew) of the flowers produce fruit, so there must be constraints on pollination to do with timing the various bits and pieces maturing, or some kind of incompatibility, all to encourage fewer but more 'productive' crossings. The fruits are big so the Cocoa Tree has a strategy of doing what it does well rather than lots of it.


The fresh seeds are covered in a white pulp which discolours to brown when the seeds are dried and fermented (by sun if you have it). You can read elsewhere about the history of chocolate in Europe, and the excitement of discovering that sugar makes it taste better, but let's just say after a slow start when Christopher Columbus disregarded what looked like goat droppings on a canoe, it took off.

Images: Outdoor trees from Xishuangbanna Tropical Flower and Plant Garden in China, cluster of flowers from Palm House at Kew Gardens, Easter egg nest and squirrel at Kew Gardens, and the rest from The Calyx and nearby (thanks to Dale Dixon and Jimmy Turner for a pre-opening tour). Thanks too to the Royal Botanic Gardens Kew webpage on Theobroma, which is where all the interesting information comes from. To hear more about The Calyx itself, listen to my interview with Dale Dixon for ABC RN's Blueprint for Living. And this is Dale examining the flower of Theobroma cacao...

Tuesday, 7 June 2016

New Guinean rhododendron a secret no longer


On the weekend I posted a picture of a big, white, vireya rhododendron flower on my Facebook page, dutifully tweeting it and 140 letters of explanation to the Twitterverse. Instagram? Nuh. Snapchat? I forgot about that the day after I joined. So old school social media.

This striking bloom is worth more than a glancing mention on social media. It deserves a ... blog post! Which, through my primitive automated social media marketing, will see it reappear on both Facebook and Twitter (and debut in the more stately rooms of LinkedIn). Still, it's worth a second glance.

The name of this plant is Rhododendron x husteinii. Now. Back in 1989, when Lyn Craven and John Rouse published their paper on its discovery, it was called Rhododendron leucogigas 'Hunstein's Secret'. You can read all about it in the Journal of the American Rhododendron Society, or rely on my potted version below.

Lyn Craven, botanist at Canberra's Australian National Herbarium for more than 30 years, began his scientific career in the plant taxonomy unit of the New Guinea Survey Group of CSIRO. He studied horticulture at Burnley Horticultural College (now part of University of Melbourne) and worked in the Parks and Gardens Branch in Canberra before settling into his position as the Herbarium.

John Rouse was a physicist as well as enthusiastic collector and grower of rhododendrons, publishing over 70 papers on their cultivation and biology. Rhododendron rousei 'John Rouse' seems to have been very much named after him! As a trustee of the Baker Foundation, he was instrumental, along with Director Phil Moors, in setting up our Australian Research Centre for Urban Ecology in 1998. He also sat on the Advisory Committee of the Maud Gibson Trust, another great supporter of the Royal Botanic Gardens Victoria.


His son Andrew Rouse continues in his horticultural footsteps, growing all kinds of rhododendrons in his backyard and small glasshouse in the inner east of suburban Melbourne. Andrew also volunteers at the Rhododendron Garden in Olinda, creating the rhododendron display inside their new glasshouse. The picture above, my social media image, is from his home glasshouse, taken on Saturday (4 June).

Now back to our secretive plant from Mount Hustein. While in Papua New Guinea in August 1966, Lyn Craven found a small seedling 'growing on a branch fallen from the forest canopy' in rainforest at 1200 metres above sea level on Mount Hunstein, in the East Sepik Province. There was only one small individual and enough material for a single cutting. The plant had large leaves but no flowers, and was tentatively assigned to species known from the region, Rhododendron schlechteri.


That cutting was sent to Melbourne where it was successfully propagated, presumably by John Rouse. When it bloomed (illustrated above, from the 1989 journal article), the large white flowers - 12 cm long and 12 cm wide - were more like another species, Rhododendron konori or its presumed cultivar/hybrid Rhododendron 'Gardenia'). However the fine detail of the plant, including the scales on the leaves, shifted its allegiance to a species called Rhododendron leucogigas (a species name very appropriately meaning 'white giant'). known only from the Cycloop Mountains in Irian Jaya.

The Mount Hunstein collection was thought worthy of its own cultivar name - 'Hunstein's Secret' - suggesting it was not exactly the same as the form found in Irian Jaya.

There is a tendency for westerners to misuse the word 'discover' but Craven and Rouse suggest that few if any humans would have seen this plant. The area is not settled and local nomads, at least after the 1960s, stick mostly to the rivers rather than high mountains.

The name Rhododendron x hunsteinii was published last year by George Argent from Royal Botanic Gardens Edinburgh, in the second edition of his Rhododendrons of the Genus Vireya. I haven't seen the book but I'm told by Andrew Rouse that molecular sequencing confirmed it is a hybrid between Rhododendron leucogigas and another species. Andrew did note on Saturday that 'it may well be a distinct species'. His flowering plant was struck from a cutting in 2004 and last flowered in 2009 - the beautiful picture at the top of the post was taken by Andrew then.


[I wouldn't normally include such an out-of-focus image but here is Andrew Rouse, to the right of Michael Hare, Convener of the Growing Friends Group, Melbourne Friends, Royal Botanic Gardens Victoria. Let's just say it was dark and misty, and the instability of my phone camera adds to the intrigue.]

Tuesday, 31 May 2016

The last waterwheels of death?


As regular readers would know, every now and then I come across a plant so compelling I feel obliged to tell its story without ever having laid eyes on it. Today it's a relative of the Sundew (Drosera) called Aldrovanda vesiculosa.

The common name - Waterwheel Plant - caught my attention. I'd just been listening to the Science Show on ABC Radio National, getting the latest on how bacteria evolved their motorised flagella and I though perhaps here was a flowering plant able to spin like a wheel.

It isn't and it doesn't, but what a plant. It consists of a floating stem with traps extending out like a water wheel. These traps work in a similar way to those of the Venus Flytrap, Dionaea muscipula, snapping shut in 1/50 of a second when an insect visitor to trips two hairs in the mature device. Charles Darwin called it the 'miniature aquatic Dionaea'.

There are lots of species of Aldrovanda in the fossil record, but only one living on Earth today. This species, Aldrovanda vesiculosa, has been recorded from Australia, Asia, Europe and Africa. Records are scatted and the species is considered to be at risk of extinction worldwide.

The map of its distribution in Australia shows a species of apparently no particular preference other than aquatic habitats more or less near the coast. It's in the north, the south and even in the south-west - but not (yet) found in Victoria or Tasmania.

As reported by Robin Wylie in New Scientist, habitat destruction and illegal collection (hence the vagueness in locality reports on the web) have meant it is down to 10% of its abundance a hundred years ago. In NSW there is a 'Saving our Species' page dedicated to its survival. There are three existing localities mapped and a fourth site flagged for relocation.


Relocation depends on gathering, storing and germinating seed, and that's yet another problem for the species (outlined in a recent paper in the Botanical Journal of the Linnean Society). A group of mostly Western Australian researchers led by Adam Cross found that only 12% of seeds could be germinated after one year. Most of them succumb to fungal attack.

The seed coat looks smooth but according to this report it has a 'honeycomb-like arrangement' which helps the seed to float but also provides an easy route for fungi to enter the seed.

Freezing kills the seed but cryostorage of actual plants or embryos may be possible. For now though, the authors suggests we protect their habitats and put more effort into finding out what stops Waterwheel Plant thriving in nature.

The Waterwheel Plant is the only aquatic plant with a trap that snaps shut to capture prey. In 1876 Charles Darwin thought this was pretty cool, and went on to show it digested water fleas and mosquito larvae. Unless we care for this plant in the wild, and support some conservation science, a mere (in evolutionary terms) 140 years later we may be witnessing the end of this strange and beguiling plant lineage.


Images: Having not seen this plant myself, these images are not mine. The top two are from Summa Gallicana, the top one originally sourced it seems from Barry Rice's sarracenia.com (who allows the use of his images subject to attribution). The close up of the 'waterwheels' thanks to Lubomir Adamec, from the US Geological Survey. While all the plants illustrated here are quite green, in Australia the Waterwheel Plant is usually reddish in colour, not unlike many of the sundews. Here is another photo by Lubomir Adamec (Carnivorous Plants) of a plant from northern Australia.