Tuesday, 22 May 2018

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...

Tuesday, 15 May 2018

Greasy green trunk a bonus in the Mexican desert


Green trunks and stems are handy if you're a plant that drops its leaves during the sunniest months or, like a cactus, you have spines instead of leaves. That way you can - if you are a plant - us the abundant energy from the sun to produce food without those troublesome appendages that lose water so easily.

My example today is the elephantine skinned, Sonoran Palo Verde: the green(verde)-sticked(palo) plant from the Sonoran Desert. Now I haven't visited the Sonoran Desert in Arizona but I have seen this plant growing in central Mexico, near Tehuacán.


Parkinsonia praecox has gathered up quite a few scientific names over the years but it's enough to know it is in the legume family, grouped with Caesalpinia and similar plants. Its natural range extends from the southern Sonoran Desert through Mexico to dryer parts of Peru and Ecuador.

A local common name is Manteco, meaning fat or lard, perhaps a reference to the buttery texture of the bark. Another is Palo Brea, meaning green pitch or tar, probably also a reference to the bark layer, which is a bit like a strip of bitumen. Or both may be because the bark of this tree has been used to tan animal skins into leather.


The resin also has its uses, including an incense sold as Peruvian Gold Copal. You too can experience the 'wonderfully unique notes reminiscent of pumpkin or butternut squash'. Good enough to eat perhaps? And you can. Laboratory tests of mice indicate that at low levels the gum could be a safe food additive.

Palo Verde is the more general name, given to any of the 12 species of Parkinsonia, all with yellow flowers and green bark. In Northern Australia the sharply-spined Mexican Palo VerdeParkinsonia aculeata, is a problem weed of pastoral land.


The species photographed here was labelled Parkinsonia praecox in the nearby Jardín Botánico Helia Bravo Hollis, a species not, as far as I'm aware, (yet) a weed in this country.


The trees in the botanic garden infected with this beetle, generating a swollen golf-ball sized home on some of the branches. I have read about a dedicated beetle, called the Palo Verde Beetle (Derobrachus geminatus), but that seems to be an entirely different kind of creature whose larvae live in the soil.

The leaves were barely visible in early April but they are your typical feathery legume leaf. A few are emerging here near one late flower.


And while often (e.g.) described as having an umbrella shape, the trees I saw were relatively young and less expansive in the canopy.



Tuesday, 8 May 2018

Temperate House reopened, this time by Sir David not QEII


It's taken five years, £41 million, the repair of 69,000 individual parts (including the replacement of 15,000 panes of glass), 180 km of scaffolding and more than 5,000 litres of paint, but Kew Gardens' Temperate House is back in action.

Designed by Decimus Burton, the gentleman who gave us the Palm House at Kew Gardens, this giant glasshouse was first opened in 1863, although with additions it was not complete until 40 years later. Queen Elizabeth II reopened it in 1981 after its last major restoration. This time Sir David Attenborough, with Kew's Chairman, Marcus Agius, and Director, Richard Deverell, did the honours last week (on 3 May 2018).


At 4,880 square metres in area, the Temperate House is twice as big as the Palm House, and the largest still-standing Victorian glasshouse in the world. For more than 150 years it has been home to plants from Africa, Australia, New Zealand, the Americas, Asia and the Pacific Island. Plants that otherwise would shiver (and die) outside in the London climate.


In the freshly renovated glasshouse you can see 10,000 plants, representing 1,500 species, displayed to highlight conservation efforts to protect our temperate forests. The famous South African cycad Encephalartos woodii remains, a species extinct in its natural habitat. Today this cycad is found only in botanic gardens and private collections around the world, and Kew's specimen is one of the finest.

Closer to (my) home is a new addition, Johnson's Grass Tree (Xanthorrhoea johnsonii) from our show-winning garden designed by Jim Fogarty, 'Essence of Australia', at the RHS Hampton Court Palace Flower Show in 2014. We estimated at the time this specimen was possibly older than Hampton Court Palace itself, built in the 16th century. (This is Richard Barley, ex of Royal Botanic Gardens Victoria and now Director Horticulture, Learning and Operations at Royal Botanic Gardens Kew, with the specimen.)


There are more plants from that show garden, plus plenty of other species from Australia. They form part of a collection from just one of seven regions gathered together in this new display.

The interpretation is also very classy, with bit-sized science, maps and colour photos. The design is crisp and elegant as well. We can thank Sharon Willoughby, also ex of Royal Botanic Gardens Victoria for this! Here are the signs, with Richard and that cycad I mentioned above...


I was delighted to be at this reopening, a chance opportunity on my way to a botanic gardens meeting in Lisbon. The restoration project began when I was working at Royal Botanic Gardens Kew, as Director Conservation, Living Collections and Estates (with responsibility for the heritage buildings as well as horticulture at Kew Gardens and Wakehurst Place and the wonderful Millennium Seed Bank Partnership).

During my two-year sojourn, the planning was completed and most of the money raised - through the Heritage Lottery Fund; Kew's Government Department home, Defra; and some sizable private donations. Between my leaving in 2013 and today, all the cleaning, repair and painting happened. A big job and a beautiful result.

For the record, here it is in July 2014, soon after the glasshouse was cleared of plants. It's a year after I left working there and at the time of the Hampton Court Flower Show...



Tuesday, 1 May 2018

A Mexican diet of smuts, succulents and soursop


I was unsure about smut-infected corn kernels for breakfast, and whether to have a full or half litre serve of guanábana juice with dinner, but all up my Mexican gastronomic experience was a delight. Most foods were inside a folded corn tortilla but other plants (and fungi) were the stars.

This is the first in a series of posts about plant life in Mexico and Cuba. I base these on my extensive experience of both countries in early April: two days and five hours in Mexico, and four days in Cuba. This allows me latitude to make multiple errors of misappropriation, misunderstanding, exaggeration, underestimation and no doubt judgement. For which I apologise.

Let’s start with the breakfast from the roadside café on the way to Tehuacán, midway through a four-hour drive south-east of Mexico City to visit the Jardín Botánico Helia Bravo Hollis. My colleagues Manuel Bonilla Rodríguez (phycologist turned restoration ecologist), his fiancé Marcia (zoologist) and father Manuel Bonilla (biologist and plant grower with interests in orchids and cacti) recommended quesadillas washed down with atole, a slightly sweetened cornmeal drink (a ‘blue maize’ version, perhaps with a little rice as well).


Manuel, the son, suggested a filling of huitlacoche, a rather unattractive but quite tasty cluster of corn kernels infected with the smut fungus, Ustilago maydis). I also tasted a little of the tangy Opuntia ‘stems’ in Marcia’s meat quesadilla, sliced and fried with lemon juice I think, plus one of the male zucchini flower in Manuel’s second serve. Here they are (unfolded), in that order...


Further along the road, we stopped for biscuits (cookies) and lollies (candy). In particular, alegría, a kind of toffee made from roasted (and puffed) amaranth seeds and sugar, and a local speciality of the region to the south-east of Mexico City. I bought a few samples to eat later, including alegría gluing together sesame, pumpkin or other seeds and nuts. The Aztecs used flour made from Amaranthus species extensively before the arrival of the Spanish but because it was linked to non-Christian religious practices, its cultivation and use was banned for some time. 


That evening, after our road trip to the cacti ‘forests’ near Tehuacán (see picture at the top of this post), we had a selection of tacos and other tortilla products, this time accompanied by a 500 ml glass of guanábana (Annona muricata), or soursop, a close relative of the custard apple. It was a favourite of my three friends, and very nice, but thankfully we chose the half rather than full litre serve – serving sizes that would make the Mexican’s northern neighbours proud. 


A final new plant I consumed that day was a cactus icy pole. The Helia Bravo Hollis botanic garden offered a wide selection of flavours based on various cactus fruits. This is Manuel, senior, enjoying his. Mine was not too sweet and sort of fruity. I'll be back in two weeks with more about the plants of Mexico and Cuba. Next week, a brief interlude from the home country.


Many thanks to Manuel and his family (below) for their warm welcome and wealth of local information, and to The Charles and Cornelia Goode Foundation for helping to support this trip and my next, to Europe.


Tuesday, 24 April 2018

South African Pelargonium in healthy shades of pink


This attractive plant in the South African collection at Melbourne Gardens sports a label identifying it as Pelargonium sidoides. When I looked for more information about the species I wondered if it was a misidentified, or mislabeled, Pelargonium reniforme.

The two species are closely related. Indeed Pelargonium reniforme was originally, back in 1860, considered to be but a variety of Pelargonium sidoides. Pelargonium sidoides is said to have smaller, darker flower, almost black in colour. In my photos these flowers don't look black - although they have a darker sheen in real life.


Luckily, as it turns out, our census says we have both species growing in the Melbourne Gardens, so I checked out presumed localities for Pelargonium reniforme and could confirm that we do have both species. This is the flower of what I'm taking to be Pelargonium reniforme on the left, with the darker, smaller flower of Pelargonium sidoides on the right. (Notice by comparing the flowers in the picture above with the right-hand flower below, how even this different setting 'changes' the colour.)


There are also reputed differences in leaf shape with those of Pelargonium sidoides heart-shaped and those of Pelargonium reniforme, consistent with the species name, kidney shaped. There is not much in it though, assuming I/we have the taxonomy and nomenclature correct! The first image here is reniforme (kidney-shaped), the second sidoides (heart-shaped).



'Heart-shaped' compared to 'kidney-shaped' usually means a bit pointier at the far end, but that's not obviously the case here. The leaves of what we are calling sidoides do tend to be a little more folded or creased half way along and near the stalk, as you can see in this next photo I took of leaves from both species, with Pelargonium sidoides on the right. But maybe we have cultivars, crosses and intermediate varieties...


The two species are from southern Africa and reasonably drought tolerant. Pelargonium sidoides is widely distributed across South Africa, from the Eastern Cape through to Johannesburg, and extending into Lesotho and Swaziland, while Pelargonium reniforme is restricted to the Eastern Cape region only. The latter species is under some threat from unsustainable collecting, even though it is widely available in horticulture - not so much threat of extinction but with the potential to disrupt local ecosystems.

Both have medicinal uses, to varying degrees, which is why Pelargonium reniforme is over harvested. Pelargonium sidoides is better known in contemporary medicine but each of them has a long history of use in traditional treatment of stomach and liver ailments, as well as respiratory complaints.

Extracts from the bitter roots of Pelargonium sidoides, traded as Umckaloabo (German) or Rabassam (Afrikaans), have been shown in clinical trials to reduce the severity of symptoms and the duration of acute bronchitis. The efficacy of Pelargonium reniforme, however, is disputed and a 2012 study confirmed it lacks a key active chemical called umckalin.


So while it may not matter too much in our garden which species is which, as with all taxonomy there can be important implications. For us, both species are attractive when in flower at the tail end of summer and in early autumn. I quite like the velvety textured leaves too, wishing I'd found them before talking textures recently with Jonathan Green on the Last Half Hour of Blueprint for Living (ABC RN). I could have told him these leaves are described as 'densely pubescent', which they are, and that with a hand lens I could show him some additional differences between the species in the kinds of hairs that create this pubescence. But possibly that wouldn't have been great radio.

Tuesday, 17 April 2018

Deadly breakfast spread from Medusa's head


In Greek mythology, Medusa has a pair of fetching wings and a hairdo of snakes. That is until she looses her head. Unlike most Greek monsters this kills her but the severed head leads to various consequences such as children arising from spurted blood and viewers of the head turning to stone. And so on.

So when a plant is called Medusa's Head you are on the look out for something gruesome, or perhaps reptilian. This is what the female flowers of Euphorbia caput-medusae looks like.


I could read into these flowers a hairdo of some kind but Plantz Africa has a far better (and correct interpretation). This plant from the Cape region of South Africa has 'multiple serpent-like stems arising from a short ... woody stem'. So it this habit that gives this plant both its species epithet and common name.

As with many of the world's garden plants, this species was described from Europe (in 1753) by the famous Swedish biologist Carl Linnaeus. It had reached the Netherlands in 1700 and was grown by Linnaeus's friend and previous employer George Clifford, a director of the Dutch East India Company. Hence the reference to a very European mythical figure rather than one from Africa.


The specimens photographed here are in our South African collection at Melbourne Gardens (in January 2018) and only a few years old. A mature plant near Cape Town, where they are common, can reach a metre across.

This is a good garden plant for a warming, drying climate. It's succulent, so it can hold water in its stem, and the leaves are rather small, so they won't loose much water. The whole plant is photosynthetic (green) so it will take maximum advantage of sunlight to produce sugars (probably taking up carbon dioxide at night, but that's another story).

Let's take another look at that flower. Like most Euphorbia, or spurges, the 'flower' is peculiar rather than pretty.


The whole thing is called a cyathium. There are five fan-shaped bracts radiating like hands from the outside of the flower. Each of these bracts has a fringe of glands. In the middle of the cyathium is a single female flower surrounded by six small male flowers - if you look carefully you'll see the yellow pollen at the tips of a pair of anthers on top of a single stamen rising out of each male flower. 

Bees visit the cyathia, but there is a twist to this. Apparently, the honey produced by bees visiting Euphorbia species is poisonous to humans but not bees. The sap of Euphorbia contains some nasty chemicals and it is these, it seems, that end up in this unwanted form of honey called Noors. 

In South African mythology there may not be a medusa, but there is a 'deity' called Gao!na who turned himself into honey 'to poison a man who had displeased him'. The honey he became, Noors, had its origins in flowers such as those of this exotically named head of snakes.

Tuesday, 10 April 2018

Lorikeets find their manna in Cranbourne gums


Back in February - in its first week - I joined a group of staff and volunteers at our Cranbourne Gardens to count birds. Actually not so much birds as bird calls (mostly), each representing an individual bird of a particular species.

After twenty minutes we had tallied 12 species (I say 'we' but let's be honest, 'they'), quite a few less than the previous survey where more than 20 had been heard or seen. One species that was more common on this occasion was the Musk Lorikeet, possibly displacing other birds with its raucous behaviour.

I'm more familiar with the Rainbow Lorikeet, which is in a different genus and more common. The Musk Lorikeet has more green with a lovely pale blue cap on its head. It's widespread in south-eastern Australia, just not as common as the Rainbow. At Cranbourne it is attracted by the flowers of the local Manna Gum, Eucalyptus viminalis subspecies pryoriana, and this year the gums were particularly floriferous.

The perfume of the Manna Gum was described to me as smoky honey. There was none of that early in the morning in early February but there were plenty of flowers, like this, attracting the noisy lorikeets. The flowers contain a rich nectar reward.


As to the real manna of the Manna Gum, that's a sweet, white material exuded from some leaves and stems in response to insect nibbling (the manna of the bible is thought to have been from a Tamarix, again bug induced). It is also eaten by birds, and mammals, providing a year-round food source when trees are not in flower. Flower time, though, is when there is more food and more feeding birds.

Our variant of the Manna Gum, subspecies pryoriana, sometimes called the Gippsland Manna Gum, is distinguished from others in the species by its bark - rough bark on trunk and main branches - and its buds and fruits - mostly in groups of three. These characters are a little blurry at the edges, and if you are keen on sorting out your local Manna Gum species you should consult VicFlora and perhaps Kevin Rule's key in the 2011 issue of the Royal Botanic Garden Victoria's scientific journal Muelleria.

The Gippsland Manna Gum is not uncommon in Victorian woodlands near the coast from Geelong to Lakes Entrance, reaching 15 metres tall at most. The tallest Eucalyptus viminalis (subspecies viminalis), in more fertile soils on mountain ranges, can be in excess of 80 metres.

Most of us know the Manna Gum as 'the koala tree' because the leaves are one of their favourite foods. We get koalas in our trees at Cranbourne Gardens, although fewer of them than Musk Lorikeets.


You can see in this picture the willow-like appearance of the leaves, although perhaps shared with many other eucalypt species, which inspired this species botanical name 'viminalis'. The subspecies, is after Canberra-based eucalypt botanist, Lindsay Pryor (1915-1998).

In case you are wondering, I didn't see, let alone photograph, a single Musk Lorikeet. But I heard plenty of them. As to koalas, not even a grunt.

Tuesday, 3 April 2018

Bowkeria and its sticky shell flower no good for oil-prospecting bees


The Natal Shell-flower Bush grows naturally in the scrub beside creeks in eastern South Africa and Lesotho (the latter a country I have visited, briefly, from South Africa). In Melbourne Gardens it grows in what we call the Southern Africa Collection, beside the pedestrian entrance to Gardens House.


As PlantZAfrica puts it, Bowkeria verticillata is a 'decorative shrub ... with soft quilted leaves and pure white, scented flowers'. But the flowers are not only white and scented, they are also a little icky to touch. According to PlantZAfrica they are 'sticky and glint in the sunshine'. Which they are, and they do.

Natal Shell-flower Bush is one of only three species of Bowkeria, all native to the same part of Africa. Siblings Henry and Elizabeth Bowker were local naturalists of renown in 1859, when the genus was named.


In Melbourne Gardens, Bowkeria verticillata is a messy shrub about 4 metres tall. The flowers, in January, are easily missed. Walking by I noticed what looked like small blobs like bubble gum among the viburnum-like leaves.


On closer inspection the flowers looked like a closed mollusc of some kind. And then I noticed the plant label with its helpful common name, Natal Shell-flower Bush. So these oyster-shaped flowers I was looking at were not abnormal and the plant came from South Africa.


The family on the label was Scrophulariaceae but there have been lots of changes recently in this branch of the Tree of Life, with what used to be a large family now split and redistributed. These days we include Bowkeria in the oddly named family Stilbaceae with 11 other genera, including Stilbe.

Contrary to reports, when I rip open a flower it does not exhibit a 'pattern of red marks' on the inside of the scalloped petals, apparently there to guide oil-collecting bees to 'oil hairs' at the centre of the flower. These bees (again according to PlantZAfrica) move the oil from the their front to hind legs and carry it there to feed larvae in the nest.

Along the way I take it they accumulate a little pollen as well, which they distribute between flowers. There doesn't seem to be any pollination advantage to the sticky flowers although I image the surface deters a few unwanted visitors.


In our flowers you can see the four anthers, neatly tucked into the pocket at the base of the flower, and the tubular female receptor (style) in the middle. But no guiding colour bands on the bit pealed away (on some flowers there are faint hints of colour...), and no oil hairs anywhere that I can see. Perhaps they are very small.

The fruit, if it sets without oil hairs and oil-collecting bees, is a 1.5 centimetre long capsule said to look like 'polished cardboard', and remaining on the plant long after it splits to release the tiny seeds. In early February, at the tail end of the flowering, I could find only these woody (cardboardy?) remains of flowers, still quite sticky.


A few of the ovaries looked like they were fertilised, so I tracked the plant through March hoping to find some mature fruit. Sadly, as we arrive at April, nothing to post about.