Wednesday, 26 March 2014

Wednesday Wildflower: Oenothera acaulis

When I was a little kid, I loved the Hans Christian Andersen story of the ugly duckling, a cygnet—teased by the ducklings for its ugliness—that turned into a beautiful swan.  This wildflower reminded me of that story.
Oenothera acaulis leaves (the left one with a seed capsule attached to the leaf axil)

Oenothera acaulis sprawls across the ground; its weak stems can't seem to stand up straight.  Its leaves are wrinkly and untidy, and look a bit like the leaves of many weedy plants.  But when its huge white flowers open just as the sun is setting, it's a transformation.
An Oenothera acaulis plant in flower.

The flowers stay open for a day, then they turn pale pink and wither.
Oenothera acaulis flower.

It's not strictly a wild flower in New Zealand, but a few people cultivate it.  I got some seeds from the Christchurch Botanical Gardens for research on seed dispersal.  It has established in my garden and this year's plants have come up of their own accord from seeds in soil where I planted it last year. Some botanists would count that as wild, but it's not the definition we used in Flora of New Zealand Vol. 4, where crossing a boundary (such as into the neighbor's yard or onto the street reserve) was needed.
Oenothera acaulis old flower withering and showing the 150 mm long floral tube.

Anyway, these huge flowers open so quickly at sunset you can watch them moving.  It's a beautiful sight.  The style is very long and sits inside a long floral tube.  The pollen has to grow all that way to reach the ovary.
Oenothera acaulis: this old flower has turned pink as it withers

My interest in O. acaulis began years ago when I grew some in Christchurch.  I'd been working on the ice-plant family Aizoaceae and I noticed that the capsules of O. acaulis were stumpy and woody; they looked more like the capsules of Aizoaceae than the usual long and slender Oenothera capsules.  So I wondered if they opened the same way.
Oenothera acaulis unopened fruit.

Most Aizoaceae have an unusual method of capsule opening; it's called hygrochasy. Hygrochastic capsules open when they're wet. Most ice plants live in the deserts of South Africa and Namibia, and wetting their capsules causes special tissues, called expanding keels, to swell. The expanding keels are attached to a non-swelling resistance tissue and their swelling generates curvature in the capsule walls that forces the capsules open.  Other ice-plants have more complex add-ons that help to splash the seeds out of the capsules using the energy of falling rain-drops.

So I picked a couple of Oenothera capsules and dropped them into a glass of water. Within 15–20 minutes they opened fully. That's a fairly slow rate of opening, but it's about what the ice-plants do. It's thought to be a mechanism that ensures they won't open until enough rain has fallen to enable the seeds to germinate and establish.
Oenothera acaulis cross section of a capsule

Oenothera capsules don't have expanding keels, but they do have four spongy internal walls (bright and pale above), and running up each of their four sides is a rigid woody vein (brown above).  The spongy walls swell when they take up water and the rigid vein constrains the swelling to force the capsule open.  In the enlarged photo below, the rigid vein is on the right, characterised by rows of thick-walled cells; the cells of the capsule's internal walls are spongy and can expand when they're wetted.
Oenothera acaulis cross section of a capsule, enlarged, and viewed under polarised light and filters to show cell arrangements and thickened walls.

This is the only time I've been scooped in my research, because while we were writing the paper about this, German botanist Hans-Dieter Poppendieck published a thorough account of fruit opening in O. acaulis (Poppendieck 1995).  He also came to this through noting the similarity with Aizoaceae.

Like the ice-plants of Africa, O. acaulis is also a desert plant, but it's from South America.  It's a remarkable example of parallel evolution, where the same function has evolved twice in unrelated plants, and the two plants have achieved the same result in ways that are structurally very different.

Also, this is a plant that can move, both when its flowers open rapidly at dusk and when its fruits open on a rainy day. It's the "ugly duckling" of the plant world.

References


Poppendieck, H.-H. 1995. Hygrochastic capsules in Oenothera (Onagraceae). Mitteilungen aus dem Institut fuer Allgemeine Botanik Hamburg 25: 99–115. 

Thursday, 6 March 2014

Wednesday Wildflower: Viola banksii

In New Zealand we have three native and 5 naturalised violets.  One of the naturalised ones is from Australia, identified in the 1988 Flora as Viola hederacea.  It's occasionally cultivated, and because it's stoloniferous it tends to spread and occasionally escapes to become naturalised.  So I was delighted on a trip to Australia last December to see a similar plant growing in the wild, in the hills inland from the Sunshine Coast.
Viola banksii in the hills near Maroochydore, Queensland
I took some photos, and posted this one on Facebook, but my Melbourne University friend and colleague Michael Bayly politely suggested that this plant is more likely to be Viola banksii.  It seems Viola hederacea is a complex of several species and it has been divided up fairly recently.  I just tucked that information away in my mind and carried on.  Incidentally when photographing that violet, here's the view if you stand up and turn around to face the other way:
Glasshouse Mts, Queensland.
Last weekend I was out walking and saw what looked like the same violet growing in a suburban garden in Wellington.  It was overhanging the footpath enough that I deemed it permissible to steal a little bit to photograph and to grow on in the garden at home.
Viola banksii, cultivated, Karori, Wellington, New Zealand.
Using the key Mike recommended and a recent paper in Austrobaileya (Little and Leiper 2013), I was able to satisfy myself that this is indeed V. banksii and not V. hederacea.  It doesn't necessarily mean the naturalised one is the same species though; I'll have to check the specimens next time I visit the Allan Herbarium at Landcare Research.

Reference.
Little, RJ; Leiper G, 2013.  Viola perreniformis (L.G.Adams) R.J.Little & G.Leiper, stat. nov., with notes on Australian species in Viola section Erpetion (Violaceae).  Austrobaileya 9: 80–101.

Monday, 10 February 2014

The Day We Fight Back

Websites all over the world are protesting today (11 Feb 2014) about surveillance of the internet, email, telephones, and other communications by government agencies of the USA, UK, Canada, Australia, and New Zealand. Most are carrying a banner. I have joined the protest in spirit, but I couldn't figure out how to paste in the code that would generate the banner on my blog, so instead I'm writing this explanation and putting in a link here that explains the protest and its aims.

For New Zealanders, I note that one political party has already promised to repeal the latest spy legislation and to close the Waihopai spy base.

Sunday, 9 February 2014

Fruiting karaka

Karaka (Corynocarpus laevigatus) is a small New Zealand tree with large fleshy fruits.  It's interesting for a number of reasons.  Its fruits were an important food resource for Māori but the kernels had to be treated to remove the toxins they contain.  It's become a weed in some parts of the world. Some botanists consider it a weed within New Zealand too, when it becomes invasive outside its presumed native range or habitats.

Right now, karaka trees are fruiting heavily.  But not all of them.  Some trees are covered in fruit and others have none or very few.  Some years ago, I wondered if this meant they had separate sexes, and was able to show that this is the explanation (Garnock-Jones et al. 2007).  Male trees do produce a few fruits, so the sexual system in karaka is best described as gynodioecy (some plants strictly female; others are inconstant males).

Here are the two trees that started this research off, photographed this month in Kelburn.
Karaka trees in fruit, Kelburn, Wellington, 2014

Here are the same two trees about 10 years ago.
Karaka trees in fruit, Kelburn, Wellington, 1998 (from Garnock-Jones et al., 2007)

On the female tree, the panicles fruit heavily, with many of the flowers (but by no means all) developing fruits.
Fruits on a female karaka tree

On males, usually a single fruit develops on each of a few panicles.
Fruits on a male karaka tree
Karaka flowers are small and white, but if you look closely you can tell the male from the female flowers.  The male flowers are actually about twice the diameter of females, open more widely, and have pollen in their anthers.  The male flowers in the photo have pollen on the stigmas, but only very few of them will produce fruits.
Karaka flowers.  On a female tree (left); male tree (right)

Reference.

Garnock-Jones PJ, Brockie RE, FitzJohn RG 2007.  Gynodioecy, sexual dimorphism and erratic fruiting in Corynocarpus laevigatus (Corynocarpaceae).  Australian Journal of Botany 55: 803–808.


Tuesday, 28 January 2014

Wednesday Wildflower: tarweed

Tarweed is flowering at the moment.  Parentucellia viscosa is an erect herb with small yellow flowers and its leaves are covered with glandular hairs so dense they feel sticky to the touch.  You'll see it in damp patches beside roads and tracks, along the edges of ditches, and wet hollows in grassland.
Tarweed, Parentucellia viscosa, Karori, Wellington
It's a hemiparasite, which means it derives some of its nutrients parasitically from other plants, but it's also green and able to generate its own energy through photosynthesis.  Full parasites (holoparasites) usually lose the ability to photosynthesise and to make green pigments, so they are often brown or pale.

Tarweed flower.
It's related to Euphrasia, another genus of hemiparasites, of which we have a large number of native species in New Zealand, and to the introduced broomrape, Orobanche, which are holoparasites.

Orobanche minor, broomrape, near Nelson.
The hemiparasites Parentucellia and Euphrasia used to be classified along with Veronica in the family Scrophulariaceae, but it was discovered a decade or so ago ago that Scrophulariaceae as it was then drawn up wasn't a natural group (of related plants).  So that previously large family has been split up. Veronica was transferred to be classified with its relative Plantago (Plantaginaceae), and Parentucellia and Euphrasia joined their relatives the broomrapes in Orobanchaceae.

Ngaio, Myoporum laetum, Wellington
Although Scrophulariaceae has been dismembered into 7–10 different families to make a more natural classification, it still exists as a much smaller family, many of them African.  Our only native member is Myoporum, ngaio.

Saturday, 14 December 2013

The Great Veronica Hunt —Part 6.

I'm writing this in Melbourne, where I'm about to fly home after a wonderful three weeks in Australia. I wasn't specifically on a Veronica hunt, but kept my eyes open anyway, just in case.

I didn't see any Veronica in Queensland or around Sydney. The first I saw was the introduced V. arvensis in Bega, a small New South Wales town.  Australia has many of the same weedy speedwells that New Zealand does, so I was more interested to see plants of the indigenous species.
Mallacoota inlet, Vic.
We spent a couple of days with friends at Mallacoota in the far east of Victoria, and there came across V. plebeia growing beside a track in coastal forest in the wonderfully-named Croajingalong National Park.
Veronica plebeia, Mallacoota, Vic.
The flowers were closed just as they often are in New Zealand, needing a warm sunny day to open.  If they don't get to open, I assume they self-pollinate, because they always seem to set fruits.

The flower below was photographed on a cultivated plant in New Zealand, where V. plebeia is widespread and considered by some botanists to be native.  It is introduced and weedy in some other parts of the world though, so it does have the ability to be invasive.
Veronica plebeia, from a cultivated plant in New Zealand.
That was it for wild speedwells the whole trip, but my sister-in-law, near Ballarat, had some small plants of another Australian native, Veronica gracilis, ready to plant out in the garden, and one of these was in flower.
Veronica gracilis, cultivated near Ballarat, Vic.
The plants are strongly rhizomatous, and this one even had a shoot coming out of the drainage hole in the bottom of its pot.

Australia has 23 native species of Veronica, classified in section Labiatoides, and they are the sister group to the large New Zealand clade (section Hebe) that includes the hebes and their relatives (Albach & Briggs 2012).  Thus, although they look much more like northern speedwells than New Zealand hebes, they are known to be more closely related to the hebes.  And because of that fact, it's misleading to classify them as Veronica unless you classify our hebes in Veronica as well.

Reference


Albach, D; Briggs, BG. 2012. Phylogenetic analysis of Australian species of Veronica (V. section Labiatoides; Plantaginaceae). Australian Systematic Botany, 2012, 25, 353363
http://dx.doi.org/10.1071/SB12014

Wednesday, 27 November 2013

Wednesday wildflower: Diddillibah wildflowers.

This week I’m on the Sunshine Coast, Queensland, visiting family before the Australasian Systematic Botany Society’s conference in Sydney next week.  We arrived last night and this morning took a short walk to get a feel for our surroundings, from Diddillibah to the Maroochy River and back.
Maroochy River
We haven’t seen much natural vegetation yet, but plenty of wildflowers and a few native Eucalypts and she-oaks.
Mangroves, Maroochy River.
Along the river are mangroves, which I assume are the same as we have in New Zealand, Avicennia marina.  It reaches its southern limit—and the southern limit of mangroves generally—at Corner Inlet, Victoria.  Here, in the warmer climate, they grow taller.
Mistletoe in a Casuarina tree.
There were mistletoes in the she-oak (Casuarina) trees near the river.
Mistletoe flower buds.
I think this little weed is Emilia sonchifolia, something I’ve collected before, in Singapore; at least I think it’s the same.  
Emilia sonchifolia

Its resemblance to sow-thistle (Sonchus) is remarkable, but it’s convergence, because this isn’t in the same tribe.
Emilia sonchifolia flower head.
The single row of involucral bracts is characteristic of tribe Senecioneae, whereas Sonchus is in the Lactuceae.

And there was a pelican on the river. Nice.