Cracking the Saxifraga crust

Let loose into the rock garden at La Thomasia, the alpine annexe of Musée et jardins botaniques cantonaux in Switzerland, it was difficult to stay tuned to the expert commentary with so many flowers to peer at and photograph. The saxifrages particularly caught my eye but I did pick up a mention of them being an 'air conditioning plant' ... or maybe an 'air conditioned plant'.

I didn't catch the whole story but I gather the white crust on the surface of Saxifraga leaves are in some way providing air conditioning for the plant. That was back in June. A few weeks later I read a brief note in the Royal Horticultural Society's magazine The Garden about a new microscopy technique revealing previously unseen detail of the cells that form this crust.

And so to the source of the story, the University Botanic Gardens at Cambridge. As the University puts it, 'the tight hummocks and large colourful flowers of many saxifrages have captivated gardeners for centuries'. And there are many, 440 in the genus Saxifraga and another couple of hundred in its family, Saxifragaceae. Mostly they grow in cold places, towards the North Pole or up a mountain, and among rocks. The location of La Thomasia, near Bex, suits many of them.

I was surprised to read that the name 'saxifraga' - Latin for ‘stone-breaker’- doesn't refer to what they do in nature but to their historical use for treating urinary stones. But that's not why I'm posting pictures from La Thomasia. It's all about those crystals.

First let's tell you what you are looking at in my pictures. The species seems to be Saxifraga callosa, although labelled in La Thomasia as Saxifraga lantoscana. I see there are cultivars of Saxifraga callosa in the trade under the name 'Lantoscana Limelight', presumably derived from what used to be called species or variety lantoscana from the 'Maritime Alps'.

This isn't the species studied by the Cambridge botanists but the white crust is there, as you can see. The first scientific report of these structures in Saxifraga was in 1890 but it took another 40 years for confirmation that this coating is found in most species of Saxifraga.

The Cambridge team chose Saxifraga cochlearis because the hydathodes, the structures in the leaf that exude the crusty material, progress from small at the base of the leaf to a 'volcano-type structure that spews out of the crust' at the leaf tip. This appealed to them.

They argue that now, 127 years on from that first nineteenth century report, we are close to a satisfying explanation of the 'inner workings' of the Saxifraga leaf. This is the result of a new cryofracture technique (cracking open the leaf while deeply frozen) to prepare plant material for viewing in a scanning-electron-microscope.

Hydathodes expel liquids onto the surface of the leaf. Sometimes called guttation, this seems to be a way for the leaf to regulate water pressure or mineral content, perhaps expel nasty chemicals and/or fight off things that might eat or kill the leaf. The crust on the leaf of a Saxifraga is what's left when the water evaporates, mostly calcium carbonate (limestone).

While we now have a better understanding of how the hydathode works the researchers still can't determine if the crusty deposits help the plant by simply allowing the exclusion of excess salt, or by providing some particular role when deposited on the leaf surface.

So I'm none the wiser as to how the air-conditioning system works. Perhaps reflecting solar radiation, perhaps by channeling air along the leaf surface (the crust are often on the margins) or perhaps by releasing a cooling layer of water (albeit salty and leaving a crust). Maybe the next papers from the laboratory and gardens of Cambridge University will help.

Islamic legacy an ornamental citrus to fight obesity

If you get the chance to journey around the Andalusian region of southern Spain, you'll see a lot of Seville or Bitter Orange (Citrus x aurantium, the 'bitter orange' group). That's because it grows well in this hot Mediterranean climate, it's shady all year and has evocative perfumes in flower and fruit.

The fruit is, as the common name says, bitter, and its oils end up in Chinotto, Grand Marnier and the candles of essential oil devotees.

In Seville, I was told, the Bitter Orange is grown because no-one will eat or use the fruit. The Brits (and I think the French), though, make marmalade out of it (with lots of pectin and sharp flavour it makes a perfect marmalade fruit).

In 1997 Professor David Mabberley sorted out the nomenclature of edible citrus, concluding that the botanical name for the bitter orange was probably based on a plant cultivated in Europe, now resting in the herbarium of Swedish nomenclatural overlord, Carl Linnaeus.

The 'x' in the name means hybrid. This is a hybrid between a pomelo (a large grapefruit like fruit) and a mandarin. You can read more about the pomelo and other hydrids in a few of my previous posts (1, 2, 3).

Within this hybrid group are both bitter and sweet oranges. Those at the bitter end have more of the pomelo (C. maxima), and those at the sweet end, more mandarin (C. reticulata) and sometimes called Citrus x sinensis.

I gather the ones with more pomelo have the distinctive winged stalk, often used to distinguish the bitter from the sweet in southern Spain. And the Bitter Orange is the landscape tree of choice.

The first orange trees arrived in Europe via the Middle East or India, originally from China or thereabouts, and the fruits would have had a thick bitter skin. The arrival of the orange tree as an ornamental plant in southern Spain seems to have come with the Moors who moved into Spain around 600 AD (although the orange trees seem to have come later). Today they feature strongly in the gardens of the alcázars and mosques throughout Andalusia.

When oranges first arrived in Europe a big belly was linked to happiness and good health (perhaps). Now of course we are (rightfully) obsessed with obesity, and about 'cures' for our tendency to over eat. The Bitter Orange has been mooted as a treatment of sorts. The fruits contain chemicals called synephrine alkaloids, like those found in an odd cone-producing plant called Ephedra. Dietary supplements from Ephedra have been banned in some countries due to adverse side effects.

Although the use of citrus oil is promising, in 2006 more clinical trials were deemed necessary 'to draw adequate conclusions regarding the safety and efficacy of Citrus aurantium ... for promoting weight loss'. However a more recent study (2016) concludes that 'bitter orange extract ... [is] ... safe for use in dietary supplements and foods at the commonly used doses'.

Personally I'd suggest you eat a little less, but enjoy the occasional toast and marmalade after exercising among Bitter Orange.   

Thanks to Jana Bate for her picture (at the top) of the orange groves within the Catedral de Santa María de la Sede in Seville, taken from the Giralda; and to Kit Wignall for being the subject of the fruit-eating experiment, photographed by Lynda Entwisle.

A toast to the Portuguese garden of John Allen

For most Australians, the gardens of Portugal are largely unknown, and unvisited: with the exception perhaps of a few around Sintra, near Lisbon, which I mentioned in passing in my Iberian posts. Many, like the country itself, seem to be looking back with a kind of melancholy to a time of prosperity and prestige.

The Quinta de Villar d'Allen, just outside the beautiful harbour city of Porto, is a garden not so much in decline but one certainly in a kind of eerie stasis. Back in June, I maneuvered our hire car to the centre of the Porto - a task requiring some art and luck - eager to check into our Pousada (the equivalent of the Spanish Parador hotel chain). As it turns out, the Pousada we booked was a few kilometres upstream along the River Douro so I had to coax our car through even narrower pedestrian streets, and back out of town.

The alternative Pousada was lovely in its own way but away from the main drag. While this meant more planning for visits into town, it did offer the opportunity to discover the local area and to seek out attractions not in the guide books. What I discovered a few hundred metres from the front gate was Villar d'Allen. Actually I had heard about this quinta, or country estate, in a talk by Richard Atkins a few months early, at a Friends of the Ballarat Botanical Gardens meeting. I have not expected to be anywhere near it, but here I was.

The garden is open to the public, by appointment. So on a morning walk into town I rang the number and organised to return that same day at 3.30 pm. We were met at the entrance by Isa Allen, and joined later by her husband Jose Alberto Allen. They are the fifth generation of Allens living in Portugal, with the first - George Allen - an early 18th century immigrant from England.

It was Alfonso Allen who bought this property, in 1839, beginning work on the garden almost immediately (keeping little, I think, of the original 18th century landscape). A key figure in the design of the garden was John Allen. I'm not sure what formal training he had but he was well connected, with his friends including the Scottish garden designer John Loudon and the creator of Pena Palace in Sintra, Ferdinand II (Alfonso, I think, also had connections to the great gardens of Portugal, sending camellias to Buçaco Palace in central Portugal).

These days the garden is a little rough around the edges, what we might describe as over-mature: with old trees and new plantings competing for space and our attention. 

Shaded under a heavy canopy are camellias, and lots of them. Most of the 400 or so specimens (perhaps up to 500) are labelled and quite a few have a connection to the Allen family. Portugal, like Australia, is unexpectedly a hot bed of camellia propagation and selection. Or at least both were. 

There is also an impressive stand of Chilean Wine Palms (Jubaea chilensis; although two of the four or five have died recently from fungal attack), a large Bunya Pine (Araucaria bidwillii), a very tall Blackwood (Acacia melanoxylon), as well as cedars and a podocarp or two. 

Mrs Allen was also keen to point out a very large Photinia and a yellow-flowered Philadelphis with a particularly sweet perfume. Although still a big garden with plenty of gardening to manage, the quinta is much reduced from the days of Alphonso and John. A large chunk of the property was excised when a new road was punched through the middle.

Like the garden, the inside of the house is preserved much as it would have been in the 19th century, with original furniture and wall coverings. I was impressed by a very large folio edition of Don Quixote (in Portuguese) and a pen (feather) used to sign the (first) constitution of Portugal in 1922. A post on the Camellias in Galica website provides some more history of the property and house.  

And when in Porto, one must drink Port. Jose Allen had joined the family wine business when young, learning to blend Port before joining the army and fighting in Africa for about four years. Now he makes small batches of port (a few thousand bottles each year), bottled under the family name.

Butterflies pollinating a milkweed risk arm and leg

Asclepias syriaca, the Common Milkweed, is most often grown in the Northern Hemisphere to encourage butterflies but it manages to also attract the wrath of farmers and environmentalists.

In North America and Europe the Common Milkweed is weedy and toxic to livestock, but the flowers do provide nectar for various butterflies and the leaves are particularly attractive to Monarchs. (Depending on the species of Monarch, they may favour this species or another Asclepias: see for example my post about butterflies on the Tropical species in the botanic garden of Buenos Aires, Argentina.)

Although the species name suggests it might be from Syria it is native to the USA and a bit of Canada. It was described first in Paris, in 1635 by French Physician Jacques Philippe Cornut, from seeds sent from Canada. Cornut compared this New World species to one from Syria and through some error, part of that descriptor became the species name applied by Carl Linnaeus in 1753.

In any case, this American plant has now spread considerably through cultivated land on that continent and also become established in central and southern Europe, through to the Middle East. Declared prohibited and noxious in Australia is hasn't yet arrived, but has the potential to enter the country inadvertently as a contaminant in crop seed.

The genus name provides a bigger hint as to why this plant is featured in a useful plant collection in Musée et jardins botaniques cantonaux, the botanic garden of Lausanne, Switzerland (where all my pictures are taken). Asklepios was the Greek god of medicine.

However the milky sap (and this sign) is a warning to take care. As is the promulgation of the species as a diuretic, emetic and purgative. Clearly this plant contains things your body might want to expunge.

Monarch caterpillars, however, can ingest the sap and not be harmed but the bitter and poisonous residue in their bodies does help protect them from predators throughout their life.

Still, flower buds and young shoots are (apparently) cooked and eaten by some humans. To what merit, I don't know. I'd suggest the structure of the flower and its mechanism of pollination are far more edifying so you might be better advised to watch the buds bloom rather than eat them.

First you'll see the buds, or flowers, in a cluster, all arising from the end of a common stalk. The buds blush pink at their tip, eventually turning red or deep pink when ready to open and reveal this...

In this picture the five outer pale green flaps, the sepals, are hidden but you can see the streaky petals, bent backwards. The inner parts of the flower are the most interesting. Those five hoods with an elongate tube project out of each and into the centre of the flower are modified 'stamen filaments', usually the stalks supporting anthers full of pollen. The hoods contain nectar, attractive to butterflies and other insect visitors.

As to the pollen, in this flower it sits in the green patches between the hoods. There are two connected sacks of pollen in each gap, together called a pollenium. It's tricky to see in my picture but the sacks like on either side of a narrow slot or slit. The pollen here hasn't yet become yellow or orange-brown, as it will do when ready to be released.

This pollenium is not unlike what you find in orchid flowers, where it is often thwacked onto the back of a visiting insect. In the case of the Milkweed, it's said that the leg of a visiting insect - a Monarch butterfly perhaps - slips into one of the slits forcing a sticky pollen sack to become attached to its upper leg.

The insect then extracts its leg, with the pollen, and flies to a new flower, hopefully (for the plant) repeating the awkward slip, this time bringing the pollen in contact with a receptive part of the female organ of the flower, which I gather is inside those slits.

Your butterfly or other pollinator might on occasion unintentionally leave a leg behind or even remain attached to the flower, and die in situ, but generally a 'happy' insect visitor leads to a happy 'plant'. A happy plant produces a fruit that starts off like this.

While this pollination system is intriguing for botanists it is rather difficult in practice and only a few flowers in a cluster will be successfully pollinated (there are also barriers to successful pollination but let's stick with the butterfly story). Typically only one or two fruits form, eventually producing the silky coated seeds responsible for the French/Swiss common name on the sign reproduced in this post (Herbe à l'ouate, or perhaps Herbe à la ouate, the Silkweed).

Note: If you want to see and learn more of the floral (and fruit) detail see the Microscopy-UK site, where Brian Johnston from Canada, home to our Common Milkweed, has posted some gorgeous close-up pictures. You can also read more about the pollination in various learned articles.

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.

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.

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...