Tuesday, 21 February 2017

Cannon ball fruits in Mexico need horses, old or new


Shading the car park in George Brown Darwin Botanic Gardens is a tree with fruits that only a horse could break open. Or perhaps an animal now extinct in Mexico and Central America, the current homeland of the Mexican Calabash, Crescentia alata.

Yep, a trip to the tropics is fertile ground for a blogging botanist, although presumably the same applies to a tropical botanist slumming it in the temperate region for a few days. Anyway, I'm close to the end of my northern Australian obsession but I couldn't resist another exotic tropical species with a cute back story.


In a learned paper on 'the fruits the gomphotheres [now extinct elephant relatives] ate', Daniel Janzen and Paul Martin hypothesise that horses and cattle may now provide a decent substitute for extinct 'megafauna'. Not just these elephant relatives but perhaps extinct horse ancestors.

The Mexican Calabash, or Jicaro, is the only member of the plant family Bignoniaceae in Janzen and Martin's list of Costa Rican lowland plants with seeds 'probably dispersed by extinct megafauna'. There are quite a few members of the pea family, figs, palms and others.

Bignoniaceae includes well known temperate trees such as the Indian Bean (Catalpa) and Jacaranda, bearing flowers with the male bits (stamens) attached to the petals, and typically the whole flower looking a bit like a trumpet or vase.


The Calabash has a shy and crooked, bell-shaped flower, followed by a hard and heavy ('cannon-ball-like') fruit. Both arise directly from the trunk or stems, making this a cauliflorous plant.


Today introduced horses crack open the ripe fruit of the Calabash in their mouth, eating and then distributing the 200-800 seeds held within a slippery pulp inside. Tests showed that 97% of seeds extracted from the horse dung and washed would germinate.

In the absence of horses, the fruit rots on the ground during the wet season and the fermenting pulp kills the seeds. The fruit drops from the tree while still green then, over a month or so, browns and ripens, with the innards becoming black and slimy. Although the pulp is sweet, it was a 'fetid' odour.


It seems likely the tree is more common in Cost Rica today than it was historically, thanks to the free-ranging horses. One consequence of the plant going through a bit of a bottle-neck when the local horses died out might have been a reduction in some pollinating animals such as bats.

The flowers of the Calabash are visited by four different kinds of bat today, and their numbers and diversity may have suffered as the horses, and then the Calabash, declined. This in turn could have led to changes to other plants species that may have depended on these bats for pollination. Such a tangled web!

Tuesday, 14 February 2017

Showy Crepe Myrtle, pride of the tropics


Pride of India is a species of Lagerstroemia (Crepe Myrtle) from China, Cambodia, Myanmar, Thailand, Vietnam, Indonesia, Malaysia, and the Philippines. As you will have noticed, not from India, although there are numerous references (logically with a common name like this) to it growing in that country.

More reliably perhaps, a scientific paper on the reproduction of the species specifies its range in India as 'across the Northern Himalayas and Western Ghats'.

The increasingly commonly planted Crepe Myrtle in southern Australia is Lagerstroemia indica, definitely from India in this case - plus a few other nearby countries - although there are other native and exotic species available in horticulture. Most of them are bursting into flower across Melbourne as I write. All up there are about 55 species of Lagerstroemia, growing naturally in Australia, eastern Asia and through into Japan.

We don't grow Pride of India, Lagerstroemia speciosa, in the Melbourne Gardens but there is (or was) a specimen in Sydney's Royal Botanic Garden, and it is commonly grown in the tropics. You will see more often around Melbourne cultivars of Lagerstroemia x matthewsii, a cross between Lagerstroemia speciosa and Lagerstroemia indica, and various mixes and selections of this hybrid and the species. My pictures of the Pride of India are from outside a church in Darwin, Northern Territory.


The species name 'speciosa' means showy or spectacular. The leaves are big, for the genus, and the flowers certainly grab your attention. They are big and in a prominent flowering stem.


The petals are crumpled, as they are in most of the family Lythraceae - a family which also includes the Victorian (apparently) native, Purple Loosestrife (Lythrum salicaria), a vigorous plant of wet areas in both our Royal Botanic Gardens Victoria sites.


You might also notice this picture the many stamens - the male parts bearing yellow anthers full of pollen. Reputedly each flower has 130 to 200 stamens.

The fruit is a capsule, splitting to released winged seeds.


The wood of the species seems to be something of which we should be particularly proud. In India, where we'll say it's native, the wood is used for construction of furniture, buildings, boats and rail sleepers. The wood is tough, durable and water resistant.

Other parts of the plant have more transient uses such as the leaves being used to make a tea, leaf extracts being used as a insulin-like treatment for diabetes, and the fruits used - somehow - to cure mouth ulcers. Take care with this plant though - some parts are 'astringent', others are poisonous.

Tuesday, 7 February 2017

Cuddling up to the Brazilian Edelweiss


This is the kind of plant you want to cuddle up next to in bed. Although perhaps just its leaves rather than the large woody base.

It's called Sinningia leucotricha, or Brazilian Edelweiss due to its place of origin and its woolly leaves reminiscent of the mountain daisy of Europe.  Those woolly hairs are at their cuddliest when young. As the leaf expands the hairs become sparser because they remain the same in total number (per leaf). 

The flowers are softly hairy - downy - as well. They are clustered above a group of usually four leaves, and their pastel orange colour and long tubular shape have evolved to suit hummingbirds (or vise versa I guess).


At the bottom of the plant, but partly above ground, is a big woody tuber (the caudex). This is enough to get the plant grown by cacti and succulent enthusiasts. It grows naturally beside other succulents, in rock crevices or on steep hillsides.


Sinningia is a genus of about 60 species in the mostly tropical and subtropical family Gesneriaceae. The species of Sinningia are all found in Central and South America, with most (like Sinningia leucotricha) found in southern Brazil (in this case the State of ParanĂ¡).

The genus was named after a gardener at Bonn University, called William Sinning. Mr Sinning raised the first seed of what became Sinningia in Europe.

According to the Sinningia & Friends website there are a few cultivars of Sinningia leucotricha around, including some with two tiers of the four leaves, and some without the distinctive blotches you can see where the tube of the flower flares out with a few round lobes.

In nature the plant has become threatened with extinction due to uncontrolled collecting - due to the beauty of its leaves and flowers. To relieve this stress, attempts are being make it easier to propagate and get into cultivation. It seems that growing under full sunlight is not recommended and 60-70% shading will give you the best vegetative development.

We have just one plant in our nursery, and none out on public display. I must tell Chris Jenek, the hort technician looking after this plant, to move into the shad.


Tuesday, 31 January 2017

Such beautifully draped foliage but no leaves


Most wattles (Acacia) don't have leaves. Instead, the leaf stalk expands into a flat blade - which to all intents and purposes acts like a leaf - and any juvenile feather-like leaves at the end of the stalk are lost. We call this expanded stalk a phyllode.

Take a look at a local Blackwood, Golden Wattle or Coastal Wattle to see what a phyllode looks like. But not, for example, a Silver Wattle which has actual real feather-like leaves!


The species I've illustrated here (in the right of the picture above) has phyllodes that are particularly long, up to 20 cm long, but only a millimetre or two wide. It's as if the evolutionary instruction didn't quite get through. Instead of forming something like a standard leaf, it's become more like a conifer or she-oak.

There are advantages in having long, thin phyllodes, particularly where this plant grows, between Litchfield National Park and Darwin. When it's hot and dry it isn't always an advantage to expose lots of leaf(-like) surface. Far better to keep some of your foliage partly shaded, with less surface area exposed to the sun all day.


This may be a successful adaptation but as a species Acacia praelongata isn't doing that well. Its restricted a scattered localities in the top bit of the Northern Territory. So while up that way with my fellow heads of Australian Botanic Gardens in October last year we helped (I think) Ben Wirf collect some seed for the George Brown Darwin Botanic Gardens, part of the Australian Seed Bank Partnership.


There seem to be about 40 species of Acacia with leaves at least this long and sometimes this narrow, but the habit and habitat of Acacia praelongata are definitely unusual. A species called Acacia murrayana has similarly long phyllodes but grows in arid areas outside the tropics and those long phyllodes have a single nerve/vein, rather than three in our species (although I'm not sure what quite to count in this photograph - one is certainly more prominent).


Unfortunately we didn't see it in flower, but the pale yellow heads stick out from a dangling stem, presumably a few weeks before we arrived to find the seed.

Tuesday, 24 January 2017

Popping out to see the upside down orchid


This is what we awoke to yesterday, the 23rd of January. A 15 cm wide, fleshy, orchid flower emerging from a basket brimming with pseudobulbs (the swollen bits at the base of the aspidistra-like leaves). It's a Stanhopea, induced into flower by either Lynda fertilising it last week or a liking for the recent warm and (particularly if we keep the water up) humid weather.

Species of this genus are sometimes called Upside Down Orchids, referring to the propensity for the flowering stem to head downwards, or slightly misleadingly Bucket Orchids, a name more often applied to the related genus Coryanthes which does have a 'bucket' as part of its floral apparatus.


We first noticed buds on Saturday afternoon (21 January), exactly one year after friends Maggie and Max Richards gave us half of their Stanhopea basket plant. We were to look after it, and try and get it to flower. Job done!

That said, it hasn't looked great for most of the time, with leaves a bit tattered and browned. We moved house in April, meaning its microhabitat changed from subtropical Hawthorn to subtropical Glen Iris, so that may not have helped. Typically it prefers the subtropics of more northern parts of Australia I suspect. Still, in its final resting place under this nectarine tree it seems happy enough. At least happy enough to flower.


The flower buds had presumably been there a day or two, or even more. After Lynda spotted the first two we noticed a younger second pair at the back of the basket. The two at the front though (below, photographed 21 January) looked like juicy, slightly deformed, capsicums, and ready to open any day...


It all happens quickly with Stanhopea so we kept vigil over the next few days. I had heard that their flowers audibly 'pop' open and it seems that mostly the popping occurs early in the morning: 5.30 am according to most reports or, if you are lucky, as late at 8.30 am.

I didn't hear a pop but at 6.00 am on 23 January this is what our flowers looked like - one open, one still shy. The open flowers are like porcelain, or plastic, depending on how much romance you want to evoke. The chunky insides must be like a theme-park ride for any willing pollinator.


In nature the flowers are pollinated in nature by a male (euglossine, or orchid) bee which visits the flower to collect aromatic substances from the waxy lips of the flower. On the way in, or out, it collects some of the orchid pollen to then carry to another flower.

And aromatic the flowers are. On the morning this flower opened there was a strong waft of a vanilla-like fragrance curling around my nose as I photographed what a male bee sees (in different colours) and experiences. In this bee-view picture, the pollen sits in a small notch behind that small pointy bit that seems to make the entrance to the ride unsafe.


It's fitting to seek information on this species from Royal Botanic Gardens Kew. Stanhopea was named by Sir William Hooker, an early Director of Kew, for a genus of orchids found mostly in tropical Central and South America.

There are now over 60 species known and I think ours is Stanhopea tigrina (Tiger-spotted Stanhopea), from Mexico, perhaps the mostly commonly grown species of Stanhopea in Australia.

Stanhopea nigroviolacea is another name you'll see around for a plant with similar looking flowers. That species was in fact named originally as a variety of Stanhopea tigrina, and in the most recent version of Plant List you'll find Stanhopea tigrina var. nigroviolacea. 'Nigroviolacea' seems to have more of the maroon colour on the floral parts than mine but I'm happy to be corrected on this (now infraspecific) identification!

Stanhopea tigrina was named and described in 1837 by James Bateman, the author of a rather large (10 volume) publication on the orchids of Mexico and Guatemala. By the time this hand-coloured lithograph by W.H. Fitch appeared in Curtis’s Botanical Magazine, in 1845, the species was 'not uncommon' in the collections of UK plant enthusiasts.


You can find Stanhopea in cultivation around Australia, in the collections of orchid buffs mostly, but not too many in Melbourne; we grow it inside our Tropical Glasshouse in the Melbourne Gardens of Royal Botanic Gardens Victoria. Our home display is modest when you see some of the pictures on the web of the underside of baskets lined with flowers, but even one of these flowers is marvel enough.

When I got home last night the second flower in the pair was open. Apparently, Lynda says, it was open at 8.30 am, when she ventured into the Gardens. So maybe one at 5.30 or thereabouts, and the other closer to 8.30, just like the interweb said.

Thank you to the Richards family for a gift that took a year to deliver, but deliver it did.

Tuesday, 17 January 2017

Pretty, leafless, and not a guinea worth


The genus name Hibbertia honors George Hibbert, a lover of plants and patron of botany. George was a fellow of the Royal Society and the Linnean Society in London, and purchased collections of preserved plants (herbaria) as well as funding collecting trips to, for example, the Cape of Good Hope in southern Africa.

If we look at this particular species (Hibbertia dilatata, above) from the Top End of Australia and compare it to those more usually associated with the name George Hibbert, you'd be looking for leaves and perhaps more yellowish flowers. The one below is your more 'typical' Guinea Flower, from Ku-ring-gai National Park.


And this one from our front yard, Hibbertia stellaris, a native to Western Australia, stretches the yellow to orange, but at least it has leaves.


There are around 250 species of Hibbertia in the world, the vast majority found in Australia but with some in Madagascar, New Guinea, New Caledonia and Fiji. Northern Territory has 50 species, with 28 of these added as new in 2010 (by Helmut Toelken) and five moved across from what used to be called Pachynema, a mostly leafless groups of plants.

Flowers of the genus Hibbertia can be yellow, orange, pink, white or red, but many species do have yellow flowers - hence the common name, Guinea Flower. The flower from the Northern Territory has white to creamish petals, but more often flushed with pink. This flower has three remaining of the five petals. Still pretty, but not conjuring up a guinea.


Pachynema means thick filaments. Filaments are the stalks that hold the sacks of pollen aloft in a flower, and these flowers have ring of stumpy bottle-like filaments just inside the petals, as you can see here (in yellow).

Like other species previously called Pachynema, Hibbertia dilatata has no leaves - although some species in that group have leaves only at the very base of the plant. The stems of such plants are photosynthetic (green) and usually flattened. In this case, very much flattened and looking like a long strap-like leaf.


As a gratuitous aside, this particular specimen was growing in a recently burnt area near Greenant Creek, in Litchfield National Park. The ants in question were nesting in the leaves of a nearby Red Paperbark (Lophostemon lactifluus); illustrated, with ants, below. You can bite their green bums off for a tangy treat.


Tuesday, 10 January 2017

Xanthostemon is a hot plant

In July 2003 I visited New Caledonia, an island of botanical treasures. I was there to collect red algae (one of those treasures) in the mountain streams, including the Chute de La Madeleine, about 100 km south of the capital Noumea. (In the foreground of this picture I took of the 'chute' is the New Caledonia Corkwood, Retrophyllum minor, a rare podocarp restricted to this area).


It just so happens this is also where some of the more intriguing plants hang out, include relatives of familiar Australian plants in the families Myrtaceae and Proteaceae. The soil is rich in nickel and other metals, giving it a deep red hue and the classification ultramafic (meaning low in silica and high in minerals).

This was one year before I bought my first digital camera but some years ago I scanned just one of the plant photos, using it as a reminder of that spectacular flora. This is the photo, of Xanthostemon aurantiacus. (You can also see this species in the Southwest Pacific Island Collection, down by Nymphea Lily Lake in Melbourne Gardens.)


Ferdinand Mueller described the genus Xanthostemon in 1857, from material collected in tropical Australia. So it was with some pleasure in October 2016 I saw and photographed Xanthostemon paradoxus, the very species Mueller collected, during a warm walk through Litchfield National Park (which is curiously about as far from Darwin as Chute de La Madeleine is from Noumea).


Mueller found his Xanthostemon pardoxus near the Victoria River, further east, and the species is relatively common across the top of Western Australia and Northern Territory. There are now known to be 45-50 species of Xanthostemon, 13 or 14 in Australia and the rest distributed throughout Pacific Islands and nearby south-east Asia.

All species have a woody fruits and mostly yellow stamens (the stiff brush-like parts of the flower topped with the pollen bearing anthers). Xanthostemon paradoxus carries the rather odd common name of Bridal Tree as well as various names from local Indigenous languages, including sometimes the apparently cross-cultural, Northern Penda,

Back in the 1950s, this species was discovered to be a 'uranium accumulator' and just recently it was mentioned again as a plant that may warrant further investigation for biogeochemical prospecting. The ease at which the uranium was washed from the leaves led to some concern in the original study that the relatively high amounts found in leaves might be due to contamination at the site rather than the plant drawing uranium up from the soil.

In terms of the species being used to locate underground deposits, presumably this also depends on whether Bridal Tree favours areas rich in uranium or simply accumulates the mineral when growing in uranium-rich soils, Do you simply map where the plant grows or do you have to grind up the leaves of each population to find out whether it's growing above uranium? Alternatively you might 'mine' the minerals directly from the plants themselves, which may be possible one day.

In any case, a brush of yellow anthers might be a hint that yellow rock is nearby. But to finish, three pictures of a third species of Xanthostemon, only found in the Northern Territory, and here nestled beside Tolmer Falls in Litchfield National Park. It's called Xanthostemon eucalyptoides, although in leaf, apart from the lack of black hairs, I would have named it Xanthostemon 'angophora-hispida-oides'...