Tuesday, 22 August 2017

Bat Plant a blood bank rather than necrotic nest


The Bat Plant doesn't have much to do with real bats. There are about 20 different species of Tacca, one in Australia but most in Asia through to tropical South America. All are pollinated it seems by tiny insects, and the flower structures are mostly quite somber in color. This one is a little different, with its white bracts (the two sail-like bits at the top).

I suppose you could say the flowers look like some kind of bat, particularly when these bracts are purplish to black. Then you might say the bracts were the bat's ears. But what about the extraordinary whiskers?  More like some alien cat, or rabbit, perhaps. Not all Tacca species have such striking facial features but the ones grown in horticulture are the showy ones.

When botanists, such as Gwynne Lim and Robert Raguso from Cornell University in the USA, look at this flower structure their minds turn to pollination, and pollinators. What would such flowers attract and how would this complex devise work to help a visiting animal take pollen from one flower to another (thus achieving 'out crossing' and opportunities for the plant to change and adapt)?

The fleshy flowers themselves are rather plain, protruding out from the ears and whiskers like a gum nut or plum of some kind.


Until recently (April 2017) most observers had assumed the flower colour and shape had evolved to mimic rotting meat or fungi. The kind of place a gnat or fly would seek out to lay its eggs, and in so doing transfer pollen. The flowers themselves, have nooks and crannies that are too small for your average carrion fly so it has been assumed gnats were the kind of insect that might be targeted by this floral design.

Alongside this conjecture was the uncomfortable fact that in the showy species - for example Tacca integrifolia and Tacca chantrieri - there seems to be a lot of self pollination. This is what happens when pollen isn't effectively moving from one flower to another, or isn't accepted for some reason by the receiving flower.

So why the gloomy coloured flowers, let alone the ears and whiskers? Lim and Raguso set out to answer this question by studying plants of Tacca cristata growing in two patches of remnant (but not pristine) vegetation in Singapore. They found female biting midges (or Ceratopogonids) the most common visitor to flowering plants. In the reported study of  Tacca chantrieri, where there was much more self-pollinatin, the researchers had found mostly trigona bees. The midges are smaller and can effectively collect pollen, because unlike the bees they can through the gaps in these flowers.


Lim and Raguso also concluded that the plant was not mimicking a lump of rotting meat or something similar, to act as a brood site for insects. Although both male and female midges like nectar, female midges have biting mouths to get blood from various animals, which they need for egg production. Colour and odours are likely to be the main attractants.

The researchers also noticed that the midges were more attracted to the vertical flowers, where pollination is likely to more likely than when the age and the male and female bits comes closer to direct contact, potentially leading to self-fertilisation.

Other visitors included rodents and macaques, although they ate the flowers rather than helped in pollination.

Images: Tacca integrifolia, the 'White Bat Flower' , in flower during March in the Royal Botanic Gardens Victoria Tropical Glasshouse.

Tuesday, 15 August 2017

Hackberry hides well in plain sight


The leaves with their slightly wonky base makes you think of elms. And indeed the European Nettle Tree used to be part of the elm family. As flagged by this common name, the ragged edges and leaf shape hint at the nettle.


While it has never been classified in the nettle (Urtica) family, Urticaceae, the European Nettle Tree is now included in a family whose closest relatives are the elms (Ulmaceae), nettles (Urticaceae) and figs (Moraceae). Celtis australis, as it's called botanically, joins Humulus lupulus, the hop plant (think beer, and sedative pillows), and Cannabis sativa, marijuana (think dope, and pain relief), and others, in the family Cannabaceae.

Celtis australis is sometimes called the Asian Hackberry, and in the two common names you have pretty much all of its native distribution - Europe through to western Asia. It was named botanically by Swedish botanist Carl Linnaeus so the epithet 'australis' would refer to south of Scandinavia. (The common name hackberry is in fact a corruption of hagberry, the name given to a bitter cherry growing up Carl's end of the continent)

The common name for all 100 or so Celtis species is hackberry, which doesn't sound that exciting, and I'd have to say the European Nettle Tree is one of those plants that doesn't demand attention. You can walk past, as I've done many times in this suburban park, without noticing it. John Grimshaw and Ross Bayton (in New Trees: Recent Introductions to Cultivation) describe the genus as 'at first sight ... undistinguished .. with no outstanding features, and ... seldom enthused over by authors'.


Even in its natural habitat this is a group of plants that are frequently overlooked. A nature column in Colorado newspaper headed up its 2012 story on two local species with the line 'few trees hide so well in plain sight as does the hackberry'. It goes on to say the hackberry 'forms no groves as does the quaking aspen .. no savannahs as does the eastern cottonwood ... [and] no forests as do the oaks ...'

It seems the hackberries are scattered among other trees, and easily 'lost in the camaraderie of crack willows and boxelders'. In my local park - and in the Melbourne Gardens for that matter - the hackberry is lost among other more showy plants (e.g., in the park, a Cape Chestnut with it's brilliant pink sprays of flowers in early summer).

Our North American naturalist goes on to lament that the wood is no good for polo or croquet balls,golf club heads, tool handles, baseball bats, wine barrels, whisky casks or fine furniture... The most productive use that we humans have found for hackberry wood seems to be for crates and pallets. The trunks rather plain but often characteristically warty.


Although there is no record of hackberry being used for recreational pleasure or medicinal treatment, the fruits are edible. That includes the thin red skin (when mature - my pictures were taken in late January) as well as the relatively large, hard stone, which would have to be mechanically crushed first I think. Apparently the seed is 'rich in protein and fats'


The hackberries are tough plants (Grimshaw and Bayton - see above - follow up their qualified derisive introduction with upbeat comments about its hardiness) and I would expect them to do well in our drying and warming Melbourne climate. Perhaps too well. The Chinese Nettle Tree (Celtis sinensis), planted commonly in Sydney, has become a weed in neglected parkland and on the urban fringe. In Queensland it is even more problematic, extending into native rainforest. The North American Hackberry (Celtis occidentalis) is a more aggressive weed, particularly in New South Wales where (along with other exotic species) it can choke river banks.

In Victoria, two Hackberry species are already relatively minor weeds: our European Nettle Tree is described in VicFlora as 'weakly naturalised near Myrtleford', with a few records also near Melbourne, and the North American Hackberry is 'weakly naturalised on Yarra River flats near Heidelberg'.

Given it is rather weakly planted down this way, perhaps it won't be such a problem.


Tuesday, 8 August 2017

Tropical Chinese botanic garden puts science in a magical setting


Still in China, to a relatively young botanic garden. The Fairy Lake Botanical Garden (Xianhu Zhiwuyuan), in Shenzhen, was opened to the public in 1988 but already has an impressive reputation for the scope of its collections. With over 10,000 species on display, set amongst 500 ha of semi-natural forest, the standouts are the cycads and ferns (the largest collections in China), and the iconic display the silicified tree garden.

Putting aside the numbers this is a particularly attractive landscape, with the botanical collections integrated seamlessly into this verdant setting. This is one of a handful of Chinese Academy of Science botanic gardens, which establishes its scientific credentials, but it is also ranked as a ‘AAAA’ scenic location in China, just on A less than the highest possible).

I only glimpsed the garden, firstly in the very hot early afternoon and then in the humid evening, as the sun set. The big scenic view at the top was taken from this shelter.


The petrified (silicified) forest though is the dramatic (iconic…) landscape. It's a collection of erect fossil trees, cycads and other evocative plantings. The trees are part concrete and part excavated sections of ‘silicified’ tree trunks (like marble when polished) mostly from north-west China.


Next stop was the scientific cycad collection, also with some evocation of habitat in the form of a vibrant mural complete with animal companions. The cycad collection began with the founding of the garden and in 2002, by then covering 30,000 square metres and including round 240 species, it was designated the ‘National Cycad Conservation Center’.


The collection includes a lot of rare species from China, as well as selections from around the world (including Australia). Some of the larger specimens seem to be ‘grafted’ on top of trunks or other material but that seems impossible so perhaps they are simply very old and odd. All of the big ones have of course been transplanted here.

Thanks to a couple of friends (see comments below the post), I can now put names on the cycads featured in the picture above the dinosaur mural. Karen Wilson tells me that the really big plants near the road are labelled Cycas pectinata and Cycas elongata, with probably more of the latter. Then Jimmy Wu chased up Ms Qing Wang, head of public programs at Fairy Lake, who confirmed the name Cycas elongata and pointed to a website featuring their pollination research on this species. 👍

This next, smaller and younger specimen, I do know the name of myself. It's Cycas debaoensis, a Red-listed species (i.e. extremely rare) from near Banshui in southern China, and surviving in the wild in a population of just over 1000 individuals.


And in this next picture, a mobile of cryptogam balls, for want of a better term. They are dangling clusters of fern-like things such as club moss (Selaginella) - I didn't have time to stop and identify their constituents.


They hand inside a, very big, shade house – around 5,000 square metres – holding part of the Botanical Gardens' rich fern collection. Plus just a few thousand orchids, begonias, bromeliads, pitcher plants and other plants that like a little shade. There is good interpretation of shade plants, with notes about their ecology and evolution.

During a contemplative moment we asked our hosts what a Chinese fairy looked like. Genuinely curious, we wondered if there was a historical figure or concept conjured up by that word (my Irish colleagues noted that fairies in their country are rather sinister in nature). Fairy is a direct translation from a Chinese word that apparently means, fairy. So no help there. Presumably, like in the West, a fairy grove or fairy lake or fairy dell is simply a romantic and apparently magical setting.

After my tours and a workshop on how botanic gardens are responding to the Anthropocene (I spoke about our Landscape Succession Plan and how we are responding to climate change and other management challenges using science and research) we stayed on as special guests for an award ceremony and concert to celebrate a botanical art exhibition organised by Fairy Lake Botanical Garden and the International Association of Botanic Gardens, as a peripheral event to the International Botanical Congress (that’s FLBG, IABG and IBC…).

Then something different.


Another side to the botanical garden, worlds away perhaps from the science and plant diversity. In this spectacular setting around a small lake (not the giant Fairy Lake) and among the penjing (bonsai) collection, we listened and watched a range of classical and modern Chinese entertainment. Flawless and fascinating. Fairy-like even. 

On the way out around 9 pm another layer was revealed as we passed streams of locals using the garden for evening strolls. This is a botanic garden with many appeals, and appealing to many.

There was even a, brief, connection to Melbourne. As part of the evening's festivities we witnessed the awarding of prizes to some of the botanical artists whose work featured in an exhibition associated with the International Botanical Congress. Two of our local favourites, Mali Moir and John Pastoriza-Piñol, got a Bronze and Silver respectively. Lovely work!


And finally, finding relief from the humid evening air, we see Diane Wyse Jackson, from St Louis, and Linhai Zhang,  from Guangzhou. Cool...


Tuesday, 1 August 2017

Perfectly baked botanic garden in the middle of China


With a starting date of 1959 (although see below), Chongqing Nanshan Botanical Garden could be considered a middle-aged Chinese botanic garden. China’s first substantial botanic gardens were created in the late 1920s and early 1930s – Nanjing in 1929, Wuhan in 1933 and Lushan in 1934 – although the first was in Hong Kong in 1871.

The number of botanic gardens in China in 1960 was only 10, low for such a large country with a rich flora and of course many people to learn about their natural environment. Things then hotted up, with a tally of 72 in 1990, 138 in 2000 and over 200 today. By world standards this total, and their quality, is exceptional and welcome.


Chongqing, with a municipal population of 30 million, is often described as one of three or four ‘oven’ or ‘furnace’ cities in China. These cities are away from the coast and get very hot in summer. I experienced a little of ‘fire’ on my visit in late July, compounded by the banquets often centred around a Sichuan hot pot bubbling with chillies and Sichuan peppers.


Nanshan Botanical Garden was opened firstly as a general park, mostly for sightseeing near the Golden Eagle statue on the top of a hill overlooking the central part of the city. In 1999 it was reopened as a botanic garden (so technically it is a post-1960 botanic garden), including scientific research, conservation projects and public programs. The garden is situated in what a ‘lower mountain area of subtropical China’, which (according to our climate modelling) makes it an excellent analogue for Melbourne in 2070.


I was met here at the front entrance by the Chairman of the botanic gardens, Mrs Jian Shi, and joined later by the Director, Mr Shaolin Zhang, head of science and camellia expert, Dr Junping Quan, and Deputy Director, Mr Jukan Wang. (And lest you question my dress sense, the Peep Tempel T-shirt was all I had to wear while my suitcase traveled to Chongqing on a flight 24 hours after me...)

Close to the main entrance is a large, relatively new glasshouse (at top of post), with three climatic zones: tropical, subalpine and arid. It is popular with visitors, often for the photo opportunities.


Beyond the glasshouse are 18 special gardens, and some well tended displays of signature plants such as lotus (Nelumbo; all growing in pots of water - see last picture of blog), sunflowers (also in pots) and a small ginkgo forest. The largest collection is the camellias, with 20,000 individuals representing at least 170 different cultivars (although more selections from the wild than selected in horticulture I think) and many rare local species.


This is Dr Quan next to a 400-year-old Camellia, one of a small number of older trees transplanted into the botanic garden. Other specialities of Nanshan include azaleas, osmanthus, flowering cherries and, more generally, rare plants of south-west China.

As elsewhere in Asia (e.g. Singapore) the botanic gardens are integrated within the Municipal Bureau of Parks, so staff have a broader responsibility beyond the botanic garden. Mr Yukun Wang, for example, has not only has responsibility for the glasshouse in the botanic garden but helped plan and build many urban parks in Chongqing, including this Central Park – not central in Chongqing but named after the famous New York park.


Interestingly, these Himalayan Cedars (Cedrus deodara) are being planted in large numbers here, and elsewhere in the city. According to our research at the Royal Botanic Gardens Victoria, this is a species already at the edge of its climate envelope in Melbourne and may not tolerate the changes we predict over the next 50 years (higher temperatures, less rain). However the climate in Chongqing is close to analogous to what we expect in 2070 so it will interesting to watch how this species survives in both locations over the next few decades.


I must end with food, an important part of any visit to Chongqing. Over a wonderful banquet, the Director, Mr Shaolin Zhang, spoke of his grand plans, including the creation of a night garden, resembling a city street and reaching up to the peak (with the Eagle). He also suggested they collaborate with us in Melbourne to our mutual benefit. On our side I can see the selection of plants for our future climate and interpretation for Chinese visitors as benefits, for Nanshan they would value training in our water and climate-change management as well as some insight into our visitor programs. We ate and toasted to this.

Tuesday, 25 July 2017

Bald cypresses and their knobbly knees


While I'm in an investigative mood, do Bald Cypresses breath through their knees? This was another question posed to me by our Melbourne Gardens Senior Curator of Horticulture, Peter Symes. Above is a cypress knee in Melbourne, and next up a collection (a 'knobble' perhaps) of knees at the South China Botanical Garden in Guangzhou (taken during a visit in 2009).


It's a common perception and two researchers at the University of Kansas, Craig Martin and Sarah Francke, believe so. In one rather simple experiment they have overturned years of alternate theory and folklore, to show that the knobbly 'aerial' roots of Taxodium distichum are, like those of mangroves, pneumatophores (literally, air stalks).


In nature, the Bald Cypress produces a lot of these woody projections from its roots, and while short and stumpy in the Melbourne Gardens they can be up to 'several metres' tall in the wild. The function of these cypress knees has been much debated although it's fair to say that until recently it has been assumed they have something to do with getting oxygen to roots in a sometimes waterlogged environment - i.e. a swamp.

While this sounds perfectly reasonable, there is actually little evidence to support the supposition or to discount alternative proposals. For example the knees might stabilise the tree in some way. They they might provide access to nutrients, perhaps by encouraging litter to accumulate and break down near the tree. Or could they be a storage organ, a place to hold excess carbohydrates for a less rainy day in the swamp.

Martin and Francke devised a rather simple experiment, measuring oxygen in the submerged (underground) roots when the knees were above water, and then when the knees were submerged. If there was less when the knees were entirely covered by water this, to their mind, proved that these knees were indeed air stalks (pneumatophores).


Happily, they found that oxygen was 'much higher' (about three times) in the roots when the knee was above water and therefore able to diffuse oxygen down into the soggy roots. Than ran various controls and concluded that there is now 'unequivocally strong evidence that cypress knees do indeed allow the diffusion of oxygen to the submerged attached root'.

Like any good scientist, they do qualify their result saying that the cypress knees may have evolved in response to things other than a need for oxygen by submerged roots. They are confident though that aeration was at least one major factor in their evolution.

You can see these knees in what we appropriately call the Taxodium Lawn, between the William Tell Rest House and The Terrace cafe, on Ornamental Lake at Melbourne Gardens. I'm not sure how much the knees are trimmed during mowing but it can't make that job particularly pleasant for our horticulturists.


There are other Taxodiums around the lake, mostly, I think, Taxodium mucronatum, the Montezuma Cypress. This species is less pyramidal in shape and tends to have weeping branches. It also lacks knees. Although it makes up for this by keeping its leaves in winter, unlike the Bald Cypress, named after this deciduous trait (in fact it's sometimes called more explicitly, the Deciduous Swamp Cypress). Both species come from swampy places in southern North America and Central America.

The taxonomy of the specimens in horticulture seems to be a bit of mess (according to Roger Spencer's Horticultural Flora of South-eastern Australia) but generally the Bald Cypress has longer leaves (about 10-15 mm), no leaves in winter and nice set of pneumatophores.


Images: Apart from the knobble photographed at South China Botanical Garden, all images are of the specimen of Bald Cypress on Taxodium Lawn, Melbourne Gardens, taken in March 2017.

Tuesday, 18 July 2017

Monster Swiss cheese plant in search of black holes


The leaf of the Swiss Cheese Plant, Monstera deliciosa, is nothing like a cheese of any kind when young. As it ages, perforations reach deep into the leaf and holes appear towards its centre. It becomes fern-like (pinnate), but with holes...


While lots of leaves have notches and crannies at their edges, its rather rare to find completely encircled holes. Interestingly, and pointing to some genetic trigger, most of the 40 species of Monstera have them, to varying degrees.

The question of how and why the holes form has taxed some of the greatest botanical minds, although mostly it has be said without much evidence. (Mostly too, at least in the nineteenth century, it taxed botanists with a venerable prénom...)


When the Swiss Cheese Plant made it to Europe from its home in the tropical rain forests of southern Mexico to Central America, it was quite a sensation. Fittingly, it was the Swiss botanist Augustin de Candolle who in 1827 first commented on their possible origin. A sign of weakness in the leaf, he said, a debilitation.

French botanist Augustin Saint-Hilaire disagreed entirely. It must be excessive vigour he exclaimed in 1840, In 1854, fellow countryman, Auguste Trécul, actually examined the leaves as they grew and found that the holes were caused by cells dying in the effected areas and that the leaf continuing on beyond them. This didn't solve the 'why' but helped with the 'how'.

In 1969, two botanists from Royal Botanic Gardens Kew, Robert (Melville) and 'F.A.' (Wrigley), confirmed that the holes were a 'necrosis' (a dying of cells). The compared them to colour blotches on the leaves of the Zebra Plant, Calathea, finding the patterns quite similar and more or less explained by the Diffusion Reaction Theory proposed by the great, and scandalously treated, mathematician Alan Turing. The theory appears describes the pattern caused by the interaction of growth promoting substances interacting with some kind of growth inhibitor. Again it's more to the how than the why.


Over the years a few whys have been suggested: for example, allowing water to drip to the ground and get closer to the roots, keeping the leaf cool, camouflaging the leaf to protect it from from animal grazing, and in recent years (2013) a rather complicated (to me) hypothesis where growth of the leaf is kept more consistent by having holes in it resulting in an advantage for a plant growing in a largely shaded habitat with dappled light.

Personally I'm attracted to the idea that holes might allow leaves to better survive hurricanes or similar dramatic wind events. I'm familiar with the punching of holes in large signs made of cloth for the same reason, and can see this being an adaptive pressure (i.e. a thing that allows the plant to live and reproduce longer).

Kit Wignall, touring with me to Spain in May, suggested it might be a way to reduce the weight of the leaf while extending it as far as possible. Which does make good sense. So perhaps I favour the combination of weight reduction, light penetration to lower leaves and a bit of hurricane protection thrown in for good luck.

For now though, it seems no-one really knows. And that's just one of the intriguing characteristics of the Swiss Cheese Plant. In case you are intending to eat the fruit, don't. At least not without some planning.


The unripe fruit, as pictured here, contains irritating chemicals such as oxalic acid. After a year or so, the hexagonal scales will dry out to reveal the white (edible) pulp of the fruit below. Alternatively, I gather, you can pick the fruit when the base starts to wrinkle and wrap it in a bag for a few days until the scales have separated.

The University of Connecticut, my source of the fruit information, also lets us into an intriguing fact about its seedlings. When they germinate the first shoot seeks out the darkest place it can. Not, just away from bright light but to where things are at their blackest. Once it finds suitable substrate - for example the base of a tree - it then sends a shoot light-ward, towards the canopy. In this case the why is pretty clear but the how I'll leave for another day.

Notes: All the pictures are from The Ian Potter Foundation Children's Garden at Melbourne Gardens, Royal Botanic Gardens Victoria, except the picture of the fruit, which was taken in my backyard at Sydney a few years back. And thanks to Peter Symes for suggesting this fascinating but still unresolved topic!

Tuesday, 11 July 2017

Texan dichondra a welcome mirage in summer


Talking Plants is resuming normal transmission! I'm back in the seat at Royal Botanic Gardens Victoria and back on the look out for flowers, gardens and other botanical treats to serve up each week.

Today, we'll ease back into things with a plant from the desert regions of southern USA and Mexico, reaching Europe (at least in dried, pressed form) in the early nineteenth century. I see it every day, in my backyard, but until I sat down next to it in a low chair, in late February, I hadn't noticed the flowers.


The silvery leaves of our Dichondra argentea 'Silver Falls' tumble from an old colander (competing with the rather rampant Ivy-leaf Toadflax, Cymbalaria muralis), and they look their best when our climate is a little more like tropical America, in our Melbourne summer.


The silver sheen is due to a covering of downy hairs which also covers the flowers, which along with their tiny dimensions (less than 5 mm across) makes them, as the Missouri Botanical Garden Plant Finder puts it, 'insignificant'. They are 'not showy', as the same site explains. All true but they are rather cute if you can get close enough.


In the following picture, you can just see the two capsules that follow the flower, providing the genus name 'dichondra', which means two grains (the grains being the ovaries or resulting capsules in fruit). 'Argentea' means silvery and I'm presuming I should use the cultivar name 'Silver Falls' for our specimen, a variant happy to dangle from a basket, or colander. 



The species Dichondra argentea was collected and named by the famous German ecologist, Alexander Humboldt and French botanist, Aimé Bonpland, after their journey through Latin America between 1799 and 1804 (the German botanist Carl Wildenow formally described the species, from their information, in 1809).
It was a good find. The genus Dichondra is a small one, currently thought to have only 15 species, most of which have creeping stems that can send down roots at the point where the kidney-shaped leaves arise. The distinctions between species can be fine but presumably the silvery sheen made this one stand out from the (small) crowd. 

Dichondra species are mostly found in the tropics but here in Victoria we have Dichondra repens, Kidney Weed, a species found naturally in I think every State in Australia (including the even more temperate Tasmania). There is possibly a second species in the north of Victoria and in other States, called 'sp. 1' in VicFlora and 'sp. A' in the Flora of New South Wales, plus the sometimes weedy Dichondra micrantha from North America and east Asia.

Interestingly, the rest of the genus is found in the Americas: North America has eight species, South America about seven. It's an odd world distribution but that's the way it is. Dichondra is in the family Convolvulaceae, with Blue Morning Glory (Ipomoea indica) and Silverbush (Convolvulus cneorum), as well as the sweet potato (Ipomoea batatas). The family as a whole is spread all over the world, apart from the colder extremities in both Hemispheres.

Dichondra argentea is a good tough plant for our impending climate in Melbourne but I do note that it didn't survive a trial on an un-irrigated roof garden in Texas. It also gets a little shy during winter but should pull through.