Tuesday, 15 March 2016

A dry summer in Wellington.

I haven't blogged here for a couple of years. I've been busy doing other things, mostly with a camera, and I'll have more to say about that in good time.

It's been a warm and dry summer in Wellington. Until Christmas it was cool, even cold, but since the beginning of January it's been much warmer than usual and very dry. Warmer than usual in Wellington isn't what most people would call warm, but daytime temperatures have stayed in the mid-20s for weeks and some nights have been uncomfortably warm. We had a shower of rain, briefly, about three weeks ago, and the last one before that was probably two weeks prior. That's pretty unusual round here, and our plants aren't used to it.
Pate, Schefflera digitata. The leaves aren't really wilting, but the swollen pulvinus at the petiole base has lost turgor, making the leaves hang down
I went for a walk yesterday to look for pigeon-wood fruit (Hedycarya arborea) in the Birdwood Reserve near the Zealandia sanctuary. The understory was very dry and many plants were wilting noticeably.
Coprosma grandifolia wilting badly
Everywhere, the soil was dry and dusty. But the wilting was most intense on the little ridges that run down the steep valley sides (this valley runs along the Wellington Fault). Interestingly, out in the open, some of the same plants showed no wilting at all. Maybe those ones are acclimated to dry conditions.
Hangehange (Genisotoma ligustrifolium) leaves are dull and wilted.
What's going on? Is this global climate change?
These fern (Microsorum pustulatum) leaves were dull and wilted, with a slightly silvery sheen.
It might be, but this year is also a very strong El Nino year. Of course the strength of the El Nino might itself be due to climate change. But in general, it's tricky to extrapolate from an extreme weather event like a hot or cold day, or even a hot or cold season, to overall long term climate trends. If we don't allow people to say a snow-storm is evidence that climate change isn't happening, we shouldn't allow people to say a heat wave is evidence that it is.
Kawakawa (Piper excelsum) starting to wilt. The leaves have curled and are hanging down.

However, long term trends show pretty clearly that the climate is getting warmer almost everywhere, and it seems that last year, and this one so far, are way warmer than even that trend would have predicted. You'd have to be pretty out of touch not to have seen the evidence in the form of temperature graphs in the news or on line.

Anyway, locally and for now the good news is that today the rain is here, and it's cold. I don't know if this rain is a drought-breaker, but with the cooler seasons approaching I guess we can expect more of it.

Did I find pigeonwood in fruit? Yes, thanks; I did.
Pigeonwood (Hedycarya arborea) fruits.

How long will it be before I start complaining about the rain and cold?

Sunday, 5 October 2014

The Great Veronica Hunt—part 7.

Spring’s here, although you wouldn’t know it today in Christchurch. I’m here for a couple of days to collect and photograph three veronicas for the eFlora project: Veronica polita, V. lavaudiana, and V. hederifolia. I've seen the last two on previous occasions, but I've never seen V. polita before, and it hasn’t been collected in a while, so I went after it first.

Most of the recent collections are from Riccarton, a suburb of Christchurch, but even so, they’re not very recent. In 1954 it was found in the grounds of Mona Vale, a stately home that now belongs to the City Council. In 1966, it was collected in Puriri Street, nearby. And in 1974 it was found on the other side of Riccarrton Road at the Riccarton Town Hall’s car park (now the Riccarton Service Centre of the Christchurch City Council). I went there first.

The car park is still there, but the old hall and much of the garden area is behind mesh fencing, such a feature of contemporary Christchurch. This is because of earthquake damage that still isn’t repaired. I poked around without success and then moved on. At this stage, it was a mild morning and I was enjoying seeing Riccarton on foot. It gave me lots of opportunity to look into little weedy patches of waste ground, flower beds and so on. One passer-by offered me a cigarette; he thought I must be scavenging for discarded cigarette butts—after all, what else could a grown man be doing groveling among the weeds.

I stopped for a coffee and hastily put on my waterproofs as a cold front swept through, and headed off up Mona Vale Road. Alongside the railway there was plenty of Veronica persica and V. arvensis, but nothing that looked like V. polita.

At Mona Vale I knocked on the door of the gardeners’ lodge, where they were very helpful. Brian showed me the likely spots, especially where a long length of brick wall had fallen down, and is now colonised by Kenilworth ivy, Cymbalaria muralis. We didn’t find any V. polita and I felt guilty keeping Brian out in the pouring rain, so I carried on alone. And then, in the part shelter of a low box hedge beside the rose garden, there it was.



V. polita is very similar to V. persica, but it has a smaller, darker flower, and a smaller, rounder, and hairier fruit. I’ve put a couple of pieces out by the window to see if a flower will open.

The pedicels are strongly recurved at fruiting, and there's a tuft of hairs at the base of the calyx, also seen in V. persica. The capsule has rounded lobes; they're spreading and rather triangular in V. persica. This one's got a tooth on the side of one calyx lobe, which is a bit unusual.

Tomorrow I'm off out to Banks Peninsula to look for V. lavaudiana, and to pick up some V. hederifolia at Lincoln on the way.

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.