Tuesday, 25 December 2012

Wednesday wildflower: centaury

Plants classified in the gentian family, Gentianaceae, have mostly radially symmetrical flowers, so when I looked closely at this common pink-flowered weed I got a bit of a surprise.  Its calyx and corolla are indeed radially symmetrical, but the stamens and style curve away to opposite sides of the flower, keeping out of each other's way.
Centaurium erythraea, Karori, New Zealand.
It shows nicely in a photo on this blog from Spain too, and in this case the flower colour is more intense.  The stigma is two-lobed, and the five stamens are bent away from it.

This separation of male and female parts in a flower is called herkogamy.  There are different kinds of herkogamy, classified according to how they function.  This looks a bit like movement herkogamy, where one sex is presented first, then moved away to make room for the other sex.  Here you might imagine that the stamens were presented in the middle of the flower, then moved to one side as the stigma grew up.  However, all the flowers I saw—young ones and old ones—were like this, so it clearly doesn't change as the flower ages.  It could be approach herkogamy, which ensures a pollinator contacts one sex first, except that a radially symmetrical flower like this can be approached from any direction.  It'll need some observations of how pollinators interact with these flowers, and that's best done in its native range, in Europe.
Gentianella, Enderby Island.
New Zealand has many native gentians, mostly white-flowered.  They're classified in the genus Gentianella.  On the subantarctic islands, flower colour is very variable, from white through to deep red.

Addendum (27 December 2012)

In Europe, centaury is pollinated by hover-flies, with a fail-safe mechanism for delayed self-pollination in the event of pollination failure (link here).

Thursday, 20 December 2012

Strange violets.

Māhoe (Melicytus ramiflorus) is one of the plants I love to show to visiting botanists from temperate Europe or North America.  They invariably ask, "What family is it?" and the answer always surprises because they're used to Viola as the representative of Violaceae.  Here's a violet that's a tree, has radially symmetrical flowers, and fleshy fruit; the world truly is upside-down in New Zealand.

Māhoe flowers on twigs of a male tree, Karori, Wellington
Well, not so fast.  It's true Viola is the type genus of Violaceae, but who said types have to be typical?  The type simply determines the application of the name according to the rules of nomenclature.  It's the circumscription—the definition of the membership of the group—that outlines its overall collective characteristics.  Violaceae is a largely tropical family, and they're woody except for Viola.  Quite a few have radially symmetrical flowers and fleshy fruits (Mabberley 2008).

A "normal" violet (Viola sp.), France.
Māhoe might be New Zealand's commonest tree.  There's certainly lots of it around Wellington, where it's an important component of the still low second growth forests that, over the last 50 years, have replaced the gorse on hills around the city.

Māhoe flowers in pulses, all the trees in a location flowering in synchrony several times a summer (Powlesland et al. 1985).  Coffee does the same thing.  The flowers are small and borne on the twigs, a form of flower presentation called ramiflory.  They're scented, especially at night, but it's not a very pleasant smell, in my opinion.
Melicytus ramiflorus, male flower.  Note the vestigial ovary in the centre and the swollen connective at the back of each anther that functions as a nectary
Melicytus ramiflorus female flower.  Note the large stigma and the nectar produced from the connective at the back of each staminode.  Female flowers are about 2/3 the size of males.
The flowers are unisexual and produced on separate trees, so a whole tree is either male or female.  The connective of the stamens and (in female flowers) staminodes is also the nectary, and each produces a glistening drop as a reward for the pollinators.
Māhoe leaf skeletons
Their leaf veins are pretty tough, but the rest of the leaf decomposes freely, to leave exquisite lacy leaf skeletons on the forest floor.
Viola cunninghamii, Hooker Valley, Mt Cook National Park.
New Zealand has three native violets (like V. cunninghamii above), plus some introduced species.  We also have quite a few Melicytus; some are small trees and others are twiggy shrubs.  Some used to be classified in the genus Hymenanthera, but that was merged with Melicytus in the 1980s.  Recent research (Mitchell et al. 2009) shows there are two pretty clear-cut groups within the genus, although the authors didn't draw attention to it, and it might make sense to recognise Hymenanthera again.


Mabberley, D.J. 2008.  Mabberley's Plant-Book (3rd ed.).  Cambridge.

Mitchell, A.D.; Heenan, P.B.; Murray, B.G.; Molloy, B.P.J., de Lange, P.J. 2009.  Evolution of the south-western Pacific genus Melicytus (Violaceae): evidence from DNA sequence data, cytology and sex expression.  Australian Systematic Botany 22(3) 143–157.

Powlesland, M.H.; Philipp, M.; Lloyd, D.G. 1985.  Flowering and fruiting patterns of three species of Melicytus (Violaceae) in New Zealand. New Zealand Journal of Botany 23: 581–596

Monday, 17 December 2012

Sun orchids

I haven't paid a lot of attention to orchids; I've been focused on other plant groups.  But I could get keen on them now, after having a look at some this week.

When I was a young lad, my Dad learned in a conversation at work that New Zealand had "a rare native orchid", and I imagined I'd never be lucky enough to see it.  Not long after, I lost my footing in what we called "the bush" (now the Wilf Mexted Reserve at Tawa), and when I'd slid to the bottom of the bank I looked at the vegetation in my hand that I'd grabbed to slow my fall.  There it was, the rare native orchid!  I'd pulled it out of the ground, maybe it was the last one.

I was too ashamed to tell anyone, until much later.  When I got to University, I found that my orchid was the common greenhood orchid, Pterostylis banksii, and that there wasn't just one species of native orchid, but lots.  Some of them are indeed rare, but many are common.  They're all interesting, in part for the exquisite shapes of their flowers and the complexity of some pollination arrangements.

Thelymitra longifolia on a bank in Karori, Wellington.
This is another of the common ones, a sun orchid, Thelymitra longifolia. Its flowers are usually white, but sometimes pink, and some people suspect there might be several species going under the one name. The bits and bobs attached to the central column are distinctive, and useful in telling if you have this or one of the other species of Thelymitra.

Thelymitra longifolia flower.
The outer parts of the flower comprise three sepals and three petals.  In most orchids the petal in the front of the flower is highly modified as the labellum (e.g., the slipper in slipper orchids), but in sun orchids all three petals are alike so the flower is quite symmetrical.  In the middle of an orchid flower, the central column combines the male and female organs.

Thelymitra longifolia, side view (left) and front view of column.
There's a single stamen and a sticky stigma, and a whole lot of other features (terminology follows Moore & Edgar 1970).  The column surrounds the stamen and stigma on three sides and extends into a hood at the top, furnished with two column arms, each with a tuft of white hairs.  Behind the stamen is a pointed post-anther lobe; you can faintly see the sides of it above, but its tip is hidden behind the hair tufts on the column arms.  The glistening knob between the anther and the stigma is the rostellum, and it's believed to be a modified lobe of the stigma.

Thelymitra longifolia is considered by some to be self-pollinating.  Charles Darwin quoted Mr Fitzgerald's Introduction to Australian Orchids that it's fertilized in the bud, although it does sometimes open enough for cross pollination to occur.  Part of the evidence for selfing is the pollen doesn't bind together into two cohesive masses, the pollinia, but the grains separate and scatter about the inside of the hood, many apparently landing on the stigma.  Also the flowers often stay closed; they only open briefly on the sunniest of days.  But if self-pollination's the whole story, then it's hard to understand why the column is so complex and how the pollen gets to the stigma without some disturbance.  In the first flower I photographed there was a thrips, a tiny pollen-feeding insect that some people believe are important pollinators.  He was head down-bum up in the anther, spilling pollen around, but none had reached the stigma.
Thelymitra venosa, here on Stewart Island, is brightly coloured and has a relatively enlarged labellum.  It's more likely to be insect pollinated.
The onion-leafed orchid, Microtis unifolia.
I photographed another orchid this week.  This one, Microtis unifolia, comes up wild in the plant pots at home.  They each have a single leaf, and a stalk of tiny green flowers, each just 3–4 millimetres across.
Microtis unifolia, note the labellum hanging down at the front of the flower.


Darwin, C. 1862.  The various contrivances by which orchids are fertilised by insects.  Murray, London. (I have the 1904 edition.)

Moore, L.B.; Edgar, E. 1970.  Flora of New Zealand. Vol. 2.  Government Printer, Wellington.

Saturday, 1 December 2012

Bring the Aurora back to Wellington.

Wellington Harbour, from Johnson's Hill.
Wellington City curves in a gentle arc around its waterfront, a vast public playground that's the envy of many other cities.  Because of its almost land-locked harbour and its position on the southern tip of the North Island, Wellington has always been a maritime city and I think it always will be.

Sculptures make the waterfront an attractive and engaging place, but imagine a tall ship here!
On any fine day, the waterfront is thronged with walkers, runners, cyclists, skaters, rowers, fishers, swimmers, diners, and sightseers, all enjoying the cafes, museums, sculptures, wildlife, and the shipping.  But it doesn't have two facilities that many other waterfront cities enjoy: an aquarium and a tall ship.
Insert tall ship here.
Others have been busy working towards an aquarium, and although it looks like it's not going to happen on the waterfront it is happening.  But for a while now I've been musing about a tall ship for Wellington.  I don't have the personality or the connections to drive such a project, but after a few years of dreaming about this, I thought the least I could do was to write a blog post and put the idea out there.

Tall ships visit here from time to time of course, and in the old days the harbour was full of them (above).  In recent years the Spirit of New Zealand and the Spirit of Adventure have been occasional visitors, and the replica Endeavour and several naval training ships have paid us a call, to great public interest and enthusiasm.  Now I think it's time the capital city had a tall ship of its own.
The Endeavour replica in Wellington Harbour.
Our tall ship would be a link with our city's 19th century origins and would emphasize our maritime environment.  It'd be ideal to have a replica of one of our first immigrant ships, such as the Aurora.  The Aurora was a one of class of elegant ships called "Blackwall Frigates".  There are plans available for the class, if not for the Aurora itself.  Wouldn't it be an adventure to build it in New Zealand!
La Hogue, a Blackwall Frigate (The Illustrated London News', August 11th, 1855)
Our tall ship would be a tourist attraction.  It would add so much to the atmosphere of the waterfront, and it could be self-funding through cruises, much as tall ships are all over the world.  In my mind I can see it moored outside Te Papa.

Tall ships everywhere often double for youth leadership and confidence training.  That's a role Wellington could value too.  Sailing such a ship in Cook Strait has got to be character-building.  The Spirit of Adventure Trust has included Wellington youngsters on its cruises, but its ship Spirit of New Zealand is based in Auckland.

Last but not least, it'd simply be cool.

How much would a tall ship cost?

I've no doubt that building a replica Aurora would be an expensive proposition well into the tens of millions, but doing it would provide training and employment here in Wellington so a fair proportion of that cost would find its way back into our economy.  Buying an existing ship would be cheaper, although it wouldn't have the historical links with the city.  Look at this lovely steel brig for example: the asking price of 4.3 million euros would leave a little change out of NZ$7M.  That's not too bad.

Who would pay for it?

Personally, I don't believe it's the city council's role to bankroll items like this, but the council does support other projects, especially when they are tourist attractions or provide employment in the region.  Public subscription is another option, with different classes of donors promised something back: maybe a cruise if you give $2000, a free visit if you give $200 or pay an annual subscription to a trust.  There are probably groups in the city, service clubs and the like, who would willingly raise funds.  And corporate donations and sponsorship should be welcomed; at least one I can think of already has a close relationship with Wellington's winds.  Ideally, the ship would be self-supporting once purchased, but that might not be realistic.  There's plenty of experience around the world of running tall ships, and no doubt lots of enthusiastic people who'd be happy to help us get started.

So what do you think?  If you like the idea, pass it along by word of mouth and social media, comment below, or just click the "cool" box at the bottom of this article.  Let's get Wellington's wind in our sails!
Mast, top, shrouds, and yard.  Endeavour replica.