Do plants sleep, or just become nycti-nasty?

The Greeks knew about it. Charles Darwin wrote about it. You have almost certainly noticed that some plants fold their leaves or close their flowers at night. Nyctinasty is just one of the things plants do when it's dark.

Other plants show nyctitropism, where a part of the plant is re-positioned. If that re-positioning happens to bring the plant to the surface of a waterbody we might call the plant nyctipelagic. The common thread here of course is 'nycti', the night.

It has been discovered recently that many more plants than we thought have nocturnal activities, if I can call them that. The Hungarian and Danish authors of a publication I was reading - thanks to a steer from colleague Peter Symes - calls them 'sleep movements'.

Their experimental site was a 'gardening shop' in Western Hungary, restricting, as they put it 'the choice of plants...somewhat'. But they managed to test a nice mix of familiar plants using a laser scanner to detect any movements in their canopy.

The scientists retested a birch tree (Betula), which had previously (in Finland and Austria) been shown to droop by up to 8 cm overnight, then return back to their original position by dawn. In that early study, the same movement was measured in trees 2000 km apart so attributed to the species rather than some kind of odd downdraft. Yet in our Hungarian gardening shop no pattern could be discerned above the 'noise'.

The Honey Locust (Gleditschia triacanthos), was the star of the Hungarian study, with its crown moving up to 9 cm overnight. Most other plants only moved up to 1 cm, in cycles of only a few hours. The Oleander (Nerium oleander) had a pattern not unlike the previously measured birch, although the movements were far less.

A maple (Acer palmatum) had, according to the researchers, a strong circadian rhythm (i.e. part of a 24 hour cycle that would occur, at least for some time, in the absence of light), but in an opposite direction to other plants. The one palm they tested, the Chusan Palm (Trachycarpus fortunei), was difficult to interpret. It doesn't have limbs to lower so all the movement was in its leaves, or fronds. They noticed a short downward movement, then up, then down, then up... Conifers, such as Cedar of Lebanon (Cedrus libani), seem to have no sleep movements.

From 21 species a few general patterns were identified. The first was what they term 'sleep', when a canopy moved significantly during the night but returned to its original position towards dawn (8-12 hours later). This sleep was considered to be a potential circadian rhythm. 

Another was called 'drift', where the plant moves but in only one direction. That is, it doesn't return to its original state at the end of the night. A third is an 'oscillation', with cycles of only a few hours, and finally there is movement best described as 'noise' - where the movements are small and difficult to detect and/or explain.

Which is all fine and interesting as far as it goes. The study is very descriptive and doesn't really answer questions about whether these cycles are circadian or controlled by the day/night cycle (all measurements were taken over a single autumn night). There is also no repeating of the tests or good controls to determine what might cause these movements. The authors realise this and suggest are range of additional experiments at the end of their paper.

As to why plants fold their leaves, close their flowers and drop (or raise) their canopy? Folding leaves is thought to reduce the loss of water from leaves during the night when the plant doesn't need to have its leaf pores open to take in carbon dioxide. Closing flowers will protect those sometimes fragile petals from wind and grazing damage while their pollinators are asleep in their beds (which obviously doesn't apply to moth and bat pollinated plants...).

Moving the canopy around, as measured in this study, might be the result of changes in turgidity of plant cells, making it truly a kind of resting state for the plant. But that's just conjecture and not entirely satisfying. What's more exciting is discovering a new phenomenon that might end up telling us a little more about how plants work, or sleep.

Image: at top, my picture of the moon on the night (31 January 2018) the Earth got in the way. The next picture is of a snowfall, at night, when we were living in Kew Gardens, London. The third is nearby, at dawn on the River Thames, from my kayak on one frosty morning. The final one is a Christmas Trees, constructed from a living conifer at Wakehurst Place, near London, photographed of course at night...

Postscript: The weekend before last there was a nice interview with one of the authors of this paper by Hilary Harper on ABC RN's Blueprint for Living.

Big foot no match for zealous collectors

Despite its common names this is of course neither a palm, a pachyderm nor a pony. Its closest relatives include other succulents such as Dasylirion and Draceana, but also things like Aspidistra, Liriope (Mondo Grass) and Ruscus (Butcher's Broom).

Elephant's Foot or Ponytail Palm are common names for Beaucarnea, a genus native to Mexico and Central America, which as you know I passed through briefly in April. This will be the last of my extended series based on a few days in Cuba and less in Mexico, but I'm sure to return later to a few of the plants I discovered on my transient travels.

There are 13 species, with Beaucarnea recurvata the best known in Australia: indeed I bought one a few weeks ago to give to my mother for Mother's Day (as an indirect memento of my visit to Mexico). In its native habitat in Mexico, however, this species is, like most Beaucarnea species, at risk of extinction. The two facts are possibly related - over collecting for horticulture is a threat to many odd and unusual plants, particularly this genus.

At Jardín Botánico Helia Bravo Hollis, near Tehuacán in Mexico, Beaucarnea gracilis was the local species, with some specimens reputedly 500 years old. It is only found in the Tehuacán Valley and although the population is in generally good shape recruitment of new plants is low. Here's another of the possible quincentenarians, and its depiction in the botanic garden logo.

At the botanic garden associated with the National Autonomous University of Mexico in Mexico City, there were at least three species grown: Beaucarnea gracilis, Beaucarnea stricta and Beaucarnea hiriartiae. This is the latter one.

All species of Beaucarnea have leaves adapted to living in arid areas, with tough narrow leaves covered in wax and sunken pores (stomata). Some species have 'grooved leaves' to further protect the pores for regulating the exchange of gases and the loss of water.

When you grow it (mum), don't over water. That swollen base is where it stores water in the arid areas of Mexico. It's happy in a smallish pot and let it dry out between waterings. In winter you can forget watering entirely. These two youngsters are in the university botanic garden.

There are quite a few plants that look a bit like the Elephant's Foot, although generally without the foot. Common in the area of Mexico I visited, and in Australian homes, is the Yucca, which is not entirely unrelated but is in a different part of the very large Asparagaceae family (yes which does include your household asparagus). This is another image from the university.

Adiós, y gracias por las suculentas!

Hibiscus survives high winds and Cuban cigars

It's time, I think, for another hibiscus. Let's head again to Mexico and Cuba where they have one of the biggest, called Hibiscus elatus, literally the tall hibiscus. You'll sometimes see it under the name Talipariti elatum, the tall talipariti, but we'll stick with Hibiscus.

You don't see this species grown much in Australia, or at least not in the south, so it feels quite exotic to me. Also it is native to the Caribbean islands, although grown elsewhere in the tropics or near tropics (e.g. Mexico) and sometimes an invasive. It's the national tree of Jamaica.

Apart from being quite tall, up to 20 or even 30 metres, this species has oddly coloured flowers. Odd in the sense that they start yellow and end red. Not unheard of in Hibiscus - another good example is the Australian species, Hibiscus tiliaceus - and known in other unrelated plants such as the rose, Rosa chinensis ‘Mutabilis’, or more famously perhaps the giant Victoria water lily. In the latter case the flowers change colour to attract, and then discourage, pollinators to help with pollen transfer between flowers. Maybe our hibiscus is simply hedging its bets, attracting insects (favouring yellow) at first and birds (favouring red) later...

The common name, Blue Mahoe, refers to the colour of the wood - which has blue-green streaks when polished - and a local or perhaps Spanish word for the species (the common name for this plant in Mexico is Majagua). The wood is said to be durable and good for cabinet making, flooring and local lutes (cuatros), amongst other things.

The fruits are cute but I didn't read of any use for them.

To bring this back to the one place in the Caribbean I've spent any time (four days to be exact), the inner layer of bark - the 'Cuba bark' - was once used to make a rope for bundling together Havana cigars. Despite this it doesn't seem to be under any major threat of extinction.

While I didn't see Blue Mahoe in the wild in Cuba, it is widely grown and the National Botanic Garden in Havana (Jardín Botánico Nacional) had a fine specimen (tree pictured above) near the venue for the conference of Caribbean and Central American botanic gardens I attended.

In Mexico I was able to examine a smaller specimen in the botanic garden within the forest of Chapultepec (Jardín Botánico del Bosque de Chapultepec) of the 500 ha parkland in Mexico City.

More than a cabinet timber, more than a string to bind cigars, the leaves of the Blue Mahoe can also provide a 'home remedy'. What it remedies is, I gather, dysentry.

If you want to grow it in Australia you need annual rainfall of above 1500 mm (or a good irrigation system I suppose) and some year-round warmth. It's said to be 'very wind-resistant' which makes it a good tree for the north of our country. Also a good choice for the botanic gardens of the Caribbean, where hurricanes are the number one threat to their tree collection.

Images: thanks to Manuel Bonilla Rodríguez for the last picture (photobombed on the left by a Blue Mahoe) and for providing a scale bar to the smaller specimen at Chapultepec.

Velvet cactus mostly displaced by Mexico City

'Feel the surface of this cactus' said Manuel (Bonilla Rodríguez), pointing at a large Opuntia in front of me. Now I've grown Opuntia in the past and I know that they have tiny little irritating 'glochids' among their spines, and you want to avoid getting them stuck in your skin (a magnifying glass and tweezers are needed to remove them all).

It turned out he meant the surface of the cactus stem (or cladode), in between the glochids and spines. It was worth it. So soft and velvety. Quite unexpected in big tough cactus.

It is the aptly named Opuntia tomentosa, its surface covered in soft, short hairs. This is not an uncommon cactus and was one of the first to be brought into cultivation in Europe from its native habitat in Mexico and Guatemala.

Indeed, according to A History of Succulent Plants (by Gordon Douglas Rowley), the Bavarian Prince-Bishop of Eichstatt was in the (late) 16th century able to brag about his giant Opuntia tomentosa: 'an estimated 3,000 joints and 5.5 metres tall with a circumference of 19 metres'. The cactus was one of only a small number of succulent plants from South Africa and Central America to feature in Hortus Eystettensis (by Basil Besler), a book published in 1613 documenting all the plants grown at Eichstatt Castle.

[This illustration is from www.plantillustrations.org where is is labelled as Opuntia ficus-indica, and indeed the label hints at that name, but Mr Rowley seems convinced it is Optuntia tomentosa.]

In Australia it is also not uncommon. The Velvet Tree Pear is a declared weed in New South Wales, Northern Territory, Queensland, South Australia and Western Australia. Generally you shouldn't grow or spread it in this country.

If you were to do so (but you can't), or you track some down as an environmental weed, you'd notice the beautiful velvet surface and the colourful flowers - mostly yellow with red outer markings. For the botanical aficionado, as with other cacti, many of the brightly coloured floral adornments are petal-like sepals (the outer, usually green appendages) rather than true petals. We call these petaloids.

In Mexico City the Velvet Tree Pear is part of the original vegetation that lined the large lake now (after draining) replaced by that city. In a restored remnant near the National Autonomous University of Mexico you can find plenty of this species nestling alongside Agave salmiana, Echeveria gibbiflora and the occasional dryland oak, Quercus deserticola.

Rhythmic rumble of hompak the sound of cultural coevolution

While on the subject of agave (see last week's post), there is one quite eccentric use I didn't mention, as a musical instrument. Not the whole plant - that wouldn't make any sense - but the hollowed out flowering stem.

The hompak is a long wooden instrument with a flared distal end. Something like an unfurled trumpet or perhaps a shortened alphorn. I can't find much background but it seems to have originated in the Mexican region during Mayan times (this next image is part of a mural I saw at the Museo Nacional de Anthropologia).

As you can see at the top of the post, my Mexican friend Manual Bonilla Rodríguez not only has one, but plays it. The extraordinary part is that he plays it, and it sounds, like an Australian didgeridoo. Cultural co-evolution says Manual.

I can attest to it sounding very similar to the didgeridoo played by the Australian Indigenous people of northern Australia. It even requires circular breathing, which although used with various more commonly encountered wind instruments is essential for creating the distinctive pulsating drone of the didgeridoo.

Here is Clarence Slockee playing the didgeridoo at the Blue Mountains Botanic Garden at Mount Tomah, New South Wales, in 2005, followed by Manual at the National Autonomous University of Mexico in 2018.

Of course you can play any long, hollowed out, tube in the style of a didgeridoo. A university friend of mine used to show off by playing a vacuum cleaner, although the sound wasn't quiet as mellifluous as that produced by wood.

There are differences between the hompak and didgeridoo. The flared end for starters. Also the source of the tube.

Above you see a didgeridoo carried in the Woggan-ma-gule ceremony held at Royal Botanic Garden Sydney on 26 January 2007. Mostly it's made from a hollowed out eucalypt branch, traditionally with the hard work done by termites.

In Mexico, it's the hollowed out flowering stem of an agave, with the trumpet end due to the flaring of the stem at its base. A small segment - maybe 15 centimetres long - of bamboo is added at the mouth end, but no wax is applied (unlike the Australian didgeridoo).

To finish, I saw another cultural pursuit in Mexico City that to my knowledge Aboriginal Australians have - quite sensibly - not taken up, Voladores de Antropologia (literally, Flyers of Anthropology). I won't go into all the details but essentially four people dangle upside down from ropes that unravel and rotate from the top of a rather long pole until the 'flyers' reach the earth. It began, I understand, in the rainforest trees of southern Mexico. Today you can, if you are lucky, see it in this park setting in Chapultepec.

On pulque, you regret the 400-rabbit nights

'Pulque is the product of a sexually frustrated agave'. That's what I said a few years ago, in a post praising the latest book by Amy Stewart called The Drunken Botanist.

It's more or less true. Pulque is a drink having a bit of revival in Mexico according to my friend Manual Bonilla Rodríguez. He likes it, although his father is more inclined to Tequila. The Spanish reported in the 1780s that about 16.5 million gallons of pulque were produced each year in Mexico. I get the sense that dropped in the early 20th century but may now be on the way up.

Both drinks are produced from the agave plant, that large blue-grey succulent you see straying occasionally into roadside verges and most noticeable when, after some 25 years, it sends up a towering flowering stalk to produce bright yellow flowers. The parent plant then dies, to be replaced by pups at its base. (And yes, that's a humming bird I captured in this close-up of agave flowers.)

To create pulque, the flower stalk is cut off before it has a chance to bloom. The base of the plant is lanced and begins to rot. Bacteria and other microorganisms move in, fermenting the sap which continues to flow as the squishy insides are scraped away.

This farming of pulque continues for many months and a single plant can produce 1000 litres or more. I said last time that that 'pulque is apparently not very nice to drink' (and has a rather stringent odour) but Manual assures me that's not the case. However he wondered if it might contain a few too many unfamiliar bugs* to make it comfortable drinking for visitors such as myself (as it happens there was no opportunity to try it).

In my recent visit I didn't advance my understanding of pulque much further but it was pointed out that Agave salmiana, a local species to Mexico City, was one that is commonly milked to produce the moderately (4-6%) alcoholic beverage. This is a specimen growing wild near the National Autonomous University of Mexico, and the specimen towards the top of this post is from the nearby botanic garden.

Pulque has a long history in the region and one of the permanent displays at the Museo Nacional de Anthropologia concerns Pulque Culture, featuring of all things, rabbits! In Aztec and other central Mexican cultures, the goddess (or female divinity) Mayahuel was strongly associated with the agave. You can see this from the symbolic image of Mayahuel at the top of my post (taken from the exhibition display), with the upper torso emerging from spiny leaves.

The agave gave the people plenty of products, such as roofing materials, fibre for ropes and weaving, tasty worms and of course pulque. It seem that the patron of pulque was the god Ome Tochtli, the 'Two Rabbit'. Drinking more than a single serve was prohibited due the fear that anyone drunk on pulque would 'fall under the influence of the Cenzon Totochtin, the 'Four Hundred Rabbits'. This would lead to loss of control, and aggressive and violent behaviour. So two rabbits good, 400 rabbits not so good.

On the way to the airport to fly out of Mexico City we passed a brightly coloured Pulqueria, a place were you might go to try the product. Unfortunately we were unable to stop for a photograph, let alone a tasting, so I give you this photograph taken on Plaza Garibaldi, Mexico City, in October 2007 (from Wikipedia Commons).

*Postscript: Paul Ward, on Facebook (5 June 2018) notes that Pulque is 'an interesting mixed culture ferment' with 'one of the main microbes ... a bacterium rather than a yeast, Zymomonas mobilis'. Paul adds that this bacterium can tolerate high alcohol concentrations, up to 15-16%, and that Pulque producers are very protective of their starter cultures.

The man in the arum, and other floral inventions in Mexican culture

A flower for every day of the year, from the Mayans to modern Mexico. That's La flor en la Cultura Mexicana, the latest exhibition at Mexico City's Museo Nacional de Antropología.

The story of floral representation over at 2000 years is told through 365 pieces. At the opening in March, the Director of the Instituto Nacional de Antropología e Historia, Diego Prieto Hernández, explained that this exhibition demonstrated that our heritage can be appreciated through aesthetic, sensual and emotional responses as well as through academic research.

There are five themes, starting with the flower as a metaphor for things of value (from pre-Spanish times).

Then its the discovery of the new world, partly through its flora, including the 16th century herbal Códice de la Cruz-Badiano, often just called the Codex, as well as 36 spectacular (yes) herbarium specimens from the National Autonomous University of Mexico (UNAM).

The third theme is the flower as an allegory for the divine, including religiously inspired oil paintings by various renowned Spanish artists and a couple of sculptural pieces.

The flower as a symbol of beauty comes next, with strong associations in eroticism and the female form. Diego Rivera's work is included here. Finally, contemporary art such as the use of flowers in displays for the Day of the Dead and fashion.

Amid all this florifery I was struck at the very start of the exhibition by Flor de granada, an 18th century silver sculpture featuring a favourite symbol of mine, the pomegranate. In this case it is said to represent the immaculate conception of Jesus. Each to his own I guess.

As with any artwork, it's story continues. Six of its petals were stolen during the Mexican Revolution, leaving only two to enjoy today.

I'm afraid you'll have to rush to Mexico City if you want to see it. The exhibition closes on my birthday, 17 June.

Papery bark wraps something like a biblical king's gift

I was about to say that if you don't live in the tropics you ain't gunna see Bursera. I couldn't recall seeing any growing around Melbourne and I don't remember it from outdoors in London. To be sure though I checked our 'living collections census' here at the Royal Botanic Gardens Victoria.

Turns out we have one listed - Bursera hindsiana from Mexico - but none seem to be surviving today. One was planted in the Arid Garden, which makes sense, and another in our Grey Garden, which is consistent with the tone of the foliage. However it's the bark I'm interested in. The red, papery bark found on so many of the Bursera species. Many but not so much this particular species.

I don't have names for all the species I photographed in Mexico and Cuba but the peeling red bark made it hard to resist taking photos (and now sharing with you). To be fair, the general absence of leaves and flowers did focus the mind a little.

The first one I saw does have a name, Bursera arida. I was in Jardín Botánico Helia Bravo Hollis, in central Mexico. On one side of me was this columnar cactus.

On the other, a rather squat and leafless Bursera arida. On close inspection you could see the distinctively papery bark.

Back in Mexico City, at the botanic garden of the National Autonomous University of Mexico, we have this (unlabelled) Burseria. Perhaps the same species.

Far away in Cuba, in the Jardín Botánico Nacional de Cuba, I walked past this next tree every morning. It's clearly a Bursera and clearly not my little stumpy Bursera arida. This particular botanic garden is unusual in labeling very few of its specimens, and this was no exception.

It may be the rather common Gumbo Limbo, Bursera simaruba, which occurs from Florida through to Venezuela, including the Caribbean. This species is also called the Tourist Tree, which works for me, and has been used as a 'living fence' (I did see a lot of living fence posts in Cuba but none looked Bursera-like to me - at least as rumbled by on the highway).

There are some 80 species of Bursera, most of them from Mexico, and all producing a fragrant resin called 'copal' (a name I mentioned last week in relation to the green-barked Parkinsonia). This resin is used for medicine, varnish and more commonly as an incense. The wider family, Burseraceae, is sometimes called the incense family, strengthened by the inclusion of genera that produce  frankincense (Boswellia) and myrrh (Commiphora).

You might find Bursaria microphylla, often called the Elephant Tree due to its slightly bloated and lumpy trunk, in the garden of a plant enthusiast in Tropical Australia*. Do let me know. I'm interested in whether any species could be described as commonly grown.

As an aside, though, not every papery barked shrub or tree in Mexico (or Cuba presumably) is a Bursera. Here is a Senecio growing in the restoration area near the University with similar looking trunk. This is a daisy, not a member of the incense family.

For Australians**, we have the beautiful West Australian Miniritchie, Acacia grasbyi, with its even more highly textured ribbons of red and brown. That one you can look up on the web.

Postscripts: *Dale Arvidsson, definitely a 'plant enthusiast' as well as Curator of Brisbane's botanic gardens, says 'Brisbane’s City Botanic Gardens has a great specimen of Bursera simaruba'

**And a few eucalypts I gather. I noticed Jane Edmundson admiring a ribbony barked gum at Melton Botanic Garden on this week's ABC TV Gardening Australia show. I'm sure there are others...