Tuesday, 30 August 2016

Knotweed looks like cure for centipede bite


Centipede Plant, Tapeworm Plant or Ribbon Bush. Take your choice - we use Centipede Plant in the Royal Botanic Gardens Victoria. All of them are apt although I think it looks more like a tapeworm myself (having never actually seen one I must admit).

Its scientific name is Muehlenbeckia platyclada. The species name 'platyclada' is pretty good too, with platus old Greek for broad and klados a branch or twig.

Although at times Centipede Plant has been included in its own genus Homalocladium - due largely to it's distinctive jointed and flattened green stems - the work of Tanja Schuster (currently the Pauline Ladiges Post Doctoral Fellow at Royal Botanic Gardens Victoria and The University of Melbourne) and colleagues from Sydney (Hi Karen Wilson!) and the USA has demonstrated it sits comfortably in Muehlenbeckia.

The old genus name 'Homalocladium' means smooth branches and the current one, 'Muehlenbeckia' honours Henri Muehlenbeck, a early nineteenth century French doctor who had an interest in plants.


There are about 19 species of Muehlenbeckia, all from the southern hemisphere: South America and various small and large islands in the South Pacific, including Australia with 11 species. This one is native to New Guinea and Solomon Islands.

It has an unmistakable form. The flat, jointed stems (when mature) do most of the heavy photosynthesis lifting with the arrow-shaped leaves sparse at the best of times and falling before flowering. While usually an unruly tangle of a bush I gather it can be coaxed into a hedge.


The flowers are small and white or green, and the berries smallish and red.


If you are familiar with other Muehlenbeckia species, the small flowers and berry-like fruits, and the simple tangled construction won't be a surprise. There are six species in Victoria, one possibly extinct and most quite rare within the State*. Muehlenbeckia adpressa, the Climbing Lignum, is the most common and found in nearly all coastal areas as well as the Grampians - it's a twining plant with larger untidy leaves.

More familiar might be Muehlenbeckia complexa, from New Zealand, which is sometimes called Maidenhair Vine - it has small circular leaves on wiry stems that can successfully obscure old fences and backyard rubbish (leading to alternative common names such as Mattress Vine and, in the UK, the geographically challenging, Australian Ivy). Although tending to weediness and established in native bushland in Western Australia, it seems to only persist only around old gardens in Victoria.

Centipede Plant itself is a little weedy in New Zealand, but then what isn't! And to be fair is seems to be limited in distribution. It has however become more of a problem in tropical areas of Asia and South America and in the latter seems to have been incorporated readily into traditional medicine where it is used to heal wounds: controlling pain and inflammation, and killing infecting bacteria. Various studies over the last decade have demonstrated the presence of active medicinal compounds in the stems and leaves of this species, at least some of those plants sourced from South America.

As non-subscriber to the Doctrine of Signatures, I'm less convinced by its reputed application specifically to bites by centipedes, except in the sense it would work on any break, inflammation or infection to the skin. You may as well recommend that it be ingested to expunge a tapeworm (don't do this by the way, it's undoubtedly poisonous), or somehow be applied to the unknotting of a particularly tangled ribbon (although as also a member of the knotweed family, Polygonaceae, it could just make things worse..)


*Neville Walsh (30 August 2016) informs me that the 'possibly extinct' species, Muellenbeckia gracillima, was in fact rediscovered near Cann River in 2002. 

Tuesday, 23 August 2016

Blueberry with greenflowers


I was waiting for these flowers to open before photographing them, then realised this seems to be as good as 灯台越桔 gets.

灯台越桔 is the common name given to Vaccinium bulleyanum in the Flora of China, and that species determination is also as good as we can get for this potted plant in our Melbourne Garden nursery.

Our horticultural botanist Roger Spencer isn't entirely happy with the way the blueberry genus Vaccinium is separated from others in the heath family Ericaceae, nor for that matter what distinguishes this particular species from things like Vaccinium venosum


All 450 or so species of Vaccinium have small cylinder-like or urn-shaped flowers, not as showy as the Papua-New Guinean species from the same family I featured a few months ago but often more so than this!

The blueberry you eat, or don't eat, is usually from Vaccinium corymbosum but a handful of other species also produce fruits we would call blueberries. Cranberries, should you eat them, typically come from either Vaccinium marcocarpon (in America) or Vaccinium vitis-idaea (in Europe).

Only 52 of the Vaccinium species are native to China, where this plant was collected by Bob Cherry in 2012. So that narrows it down a little.


Based on advice from a botanical visitor some time ago we had originally filed this specimen under Vaccinium kachinense but that species doesn't have leaves with these jagged edges, or arranged in an apparent whorl of 7 to 10 like this one.


That number of leaves remains a problem when we look at the other 51 species. According to Roger, the couplet in the identification 'key' asks us to choose between 5 to 6 or 9-10. If you head down the latter pathway other characteristics don't make sense, so for now we are assuming we have slightly innumerate Vaccinium bulleyanum which typically at least has leaves in whorls of 5 to 6.

Roger concludes that his identification is 'dubious', based on information to hand, but the best we can do for now. If it is indeed this species, it hails from shaded mountain valleys in the west of Yunnan province. 

It was described in 1912 by Friedrich Diels, in the journal of Royal Botanic Garden Edinburgh, as a species of Agapetes, a related small genus of mostly climbing plants. The description was based on material collected by the Scottish botanist George Forrest in 1905, and the number of leaves per whorl is not specified.

Forrest named the species after his patron, Arthur Bulley, who ran a nursery and public garden in Ness. Whether Mr Bulley appreciated being honoured by this drab-flowered species, I don't know.


Tuesday, 16 August 2016

A six-headed literary monster (Plant Portrait XIV*)


One of my subscription podcasts, Frank Delaney's Re: Joyce, is a reading and explanation of James Joyce's Ulysses in more or less weekly installments over 10 or so years. Delaney can be pretentious, mawkish and a little tiresome in his delivery but it's worth persisting with if you love Joyce and his perfect order of words.

In mid-June this year Delaney began dissecting chapter/episode nine, 'Scylla and Charybdis'. In the original Ulysses story, by Homer, Scylla is a six-headed monster and Charybdis is ... a whirling maelstrom. Transferred into Joyce's story, according to experts, the two monsters become philosophers, and we listen to a tussle between the idealised forms of Plato and the pragmatic logic of Aristotle (in this text represented by one of the heroes, Stephen Dedalus). It's about rhetoric, borrowing the super power of both Homer's creatures - their ability to persuade with words.

Anyway, I'm listening to Delaney read this chapter and tell what he thinks it means. On hearing the word Scylla I immediately of course thought of the plant genus Scilla. And then wondering if there was a genus called Charybdis. Which it turns out there is, sort of. Plant relatives of Scilla, as well as a group of marine custaceans, have been called Charybdis (like modern-day China and Hong Kong, biological nomenclature is one country and two systems, allowing the multiple of genus names).

The plants once called Charybdis are now included in Drimia, a genus grouped together with Scilla in the a subfamily (called Scilloideae) in the family Asparagaceae. This is all part of the recent reclassification of lilies and the like so it might sound a bit odd (like the siren call of a sea creature from a Mediterranean island perhaps). It used to be in the Hyacinthaceae, linking it to garden plant you'll know.


Scilla and what were once called Charybdis include bulb-forming species from Africa and around Homer's sea, stretching through to Asia. But not to South America. Yet words can persuade us differently. This is Scilla peruviana, growing in the shadow of the mountain photographed (2008) at the top of the post.

Despite the name the mountains are not in Peru, but in the south of Spain, in the Sierra del Pinar. I gather from Wikipedia that Carl 'father-of-plant-nomenclature' Linnaeus was apparently given specimens from Spain that arrived on a ship called 'Peru', leading him to mistake its origin.

Scilla was known to the Ancient Greeks as Skilla, which the Romans turned into Scilla, then Squilla. Our friend Linnaeus punted for Scilla, although again botched things up a little, requiring some later tidying up of the appellations. The flowers of Scilla have six each of the various parts but whether the flower is name after the monster or the monster after the flower, I don't know.

And speaking of places where things may or may not have occurred, the island of Madeira may or may not be Circe, which Homer refers to in his tale and Joyce uses as his informal name for chapter/episode fifteen. I've posted before on the giant quill of Madeira, Scilla madarensis, including the following picture of Graham Ross and me next to one at Kew Gardens in 2012.


Frank Delaney won't get to this point in the story for another year or two.

*Occasional posts are called Plant Portraits (in brackets after the blog title and marked with an asterisk). These are usually about things other than, but including at least passing reference to, plants. Often they will be inspired by a book or something else in my cultural life. The idea is borrowed (very loosely and with due deference) from Milan Kundera's 'Novels, Existential Soundings', in his Encounters. These essays were as much, or more, about things other than the book being reviewed.

Tuesday, 9 August 2016

Restrained sunflowers reveal internal clock


It's official! The flowering head of a sunflower arcs during the day in response to its own internal clock. No longer do I need to stare at sunflowers and ponder, as I did in 2009.

It's been known for at least a century or more that young sunflower plants (with their flowerheads unopened) track the sun from it rising in the east to its setting in the west, then get themselves sorted overnight so they can do the same the next day. Once the giant yellow flowerhead opens, it stops moving about and faces east. But why and how?

University of California study published in the journal Science sets the record straight. Helianthus annuus has a circadian mechanism, or 'internal clock', behind its solar tracking, and then some internal signalling to position its mature flowerheads eastward. This combination leads to more vegetative growth and improved pollination.

The solar tracking is caused by different growth rates on the sunny and shady side of the stem. During the day the cells on the east side grow a little faster than those on the west, and then vice versa at night.


Postdoctoral fellow Hagop Atamian and colleagues at University of California in Berkeley,  tested plants in pots, growth chambers and in paddocks. Somewhat cruelly - if you think all this makes a sunflower sentient (which as it happens, I don't) - they staked some plants so they couldn't respond at all. Others were turned around each day to disorientate them.

The stalked plants grew less than those that could track the sun. If the light source was kept static (in growth chamber) the plant swept east to west for a few days, then stopped. This, they say, 'is the kind of behaviour you would expect by a mechanisms driven by an internal clock'.

If the played around with the length of the day they found the plant lost its rhythm at 30 hours, so the cycle has some constraints like a clock rather than just responding directly to daylight and the sun. Light is the primary driver for growth, but there is an internal clock (a circadian rhythm) controlled to some extent by the direction of the light, that causes the solar tracking.


This all stops when the elongation of the stem stops and the best orientation for an open flower is facing the morning sun - 'eastward-orientated flowers are warmer than westward-orientated flowers' - and warm flowers attract bees (five times as many when the flower faces east).

All this is controlled by genes and signalling chemicals called auxins (for more of the gory micro-detail, track down those references above). For those of you worried about the poor experimental plants constrained to face west every day, the researchers found that a portable heater quickly brought the pollinators buzzing back.

Images: sunflowers from Observatory Gate display in December 2014, plus the middle one from the beds near the National Herbarium of New South Wales at Royal Botanic Gardens Sydney a few year back.

Tuesday, 2 August 2016

Neither palm nor lily


The commonly grown Palm LilyCordyline australis, is, somewhat surprisingly perhaps given its species name (although austral just means southern) from New Zealand. We also call it the Cabbage Tree, not the Cabbage Tree Palm, which refers to Livistona australis, a true palm and truly from Australia.

The species illustrated here is Cordyline petiolaris, growing in the Australian Garden at Cranbourne Gardens. This Broad-leaved Palm Lily is from coastal and near-coastal parts of northern New South Wales and southern Queensland.


All up there are about 20 species of Cordyline eight from Australia. There are many in cultivation, including some brightly coloured cultivars, and they are tough plants as long as you don't have frosts. For more on how to grow them and the horticultural forms, check out the International Cordyline Society website.

But what kind of plant is this Palm Lily? Well, it's neither a palm nor a lily (or a cabbage for that matter). It sits in the family Asparagaceae, with things like ... yes, asparagus. To be fair, most things in this family were once included in the Liliaceae, which is where true lilies reside.

The Palm Lily's cluster around the Mat Rush Lomandra and you sometimes see it put in the family Lomandraceae. Or Agavaceae (with Agave). Or Asteliaceae (with the Pineapple Lily, Astelia). Or Laxmanniaceae (with the Wire Lily, Laxmannia).

Or Dracaenaceae, with Dracaena, including the Dragon Blood Tree and other common ornamentals. Sometimes Dracaena and Cordyline get confused but scratch below the surface (of the soil) and you can tell them apart - Dracaeana has orange roots, Cordyline white.


Anyways, today the DNA tells us Cordyline is best included in Asparagaceae. This giant asparagus might look like a palm from a distance but close up  you'll see it doesn't have the single crown of leaves and the compound (feathery or fan-shaped) leaves pleated down the middle when young. And flowers, molecules and other bits and pieces are different.

While the flowers and fruits are not stalked, abutting their common stem (distinguishing the Broad-leaved Palm Lily from some of the cultivated exotic Cordyline species), the leaves have long stalks - or petioles - as celebrated in the species name 'petiolaris'.

In its native rainforest or wet eucalypt forest the Broad-leaved Palm Lily will reach five metres tall, but in most gardens it tends to settle at something like two metres; I suspect those at Cranbourne Gardens will seek greater heights, if we can offer them a little protection.

As to those gorgeously red berries that look like they'd make a fine jam or pie. I gather the giant moas in New Zealand ate the fruit of Cordyline australis, as do various non-extinct birds today. The fruits of Cordyline petiolaris are described as 'edible' and also 'eaten' but the interweb isn't awash with recipes for humans (or birds). More usually it's the leaves and roots of Cordyline that are eaten.



Tuesday, 26 July 2016

Australia's Black Wattles a flight hazard in China


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

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

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


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

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


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

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


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

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


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

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

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

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

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

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

Tuesday, 19 July 2016

A wild and toxic tomato


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

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

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

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


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

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

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

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


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

Tuesday, 12 July 2016

Brained agents discover gambling peas


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

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

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


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

This is how Current Science illustrates it:


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

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

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

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

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


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

Tuesday, 5 July 2016

Bloody Australian citrus


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

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

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


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


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

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

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


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

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

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

Tuesday, 28 June 2016

Australian nonsmoking plant


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

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

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


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

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

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


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

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

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

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


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

Tuesday, 21 June 2016

Gourds of two sizes needed for Papuan heath


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

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

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

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


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

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


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


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

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


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

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