Friday, 30 September 2011

Plants of the Rugby World Cup 4.—Scotch thistle.

This weekend’s big game is England vs Scotland.  I covered the Sassenach rose last week; so now it’s time to think about the scotch thistle.
As with the shamrock, there seem to be differing opinions about what is the true scotch thistle. Wikipedia says the scotch thistle is Onopordum acanthium, often also known as cotton thistle.  I’ve been told by a Scotsman (a piper who was wearing a kilt at the time) that it’s knapweed (Centaurea nigra).  But usually in New Zealand, and often in Scotland too I believe, the name is applied to Cirsium vulgare, sometimes known as spear thistle.

The point of this post is that what many would call the flower of a thistle is in fact a cluster of florets, tiny individual flowers.  Together they function as a blossom, an object that a pollinator visits.  A thistle floret has an ovary at its base, a purple tubular corolla that opens into five lobes, five stamens hidden inside the corolla tube, and a style with two stigmas.  Hundreds of these are crammed into a head, and each one eventually makes a small one-seeded fruit with a downy parachute attached.
This way of arranging flowers into heads is a feature of the daisy family, Asteraceae.  In many daisies there are two sorts of florets, the petal-like ray florets on the outside of the head, and the tubular disk florets in the centre.  In thistles there are no ray florets and it seems the whole head is made of disk florets.  In dandelions and chicory on the other hand all the florets are flattened and look like rays, although technically they’re not quite the same as true rays.
A flower head of Aster showing ray florets (white) and disk florets (yellow)
Usually in daisies, the ray florets are female and the disk florets are hermaphrodite, so the plants can easily vary in their femaleness by altering the proportions of floret types.  In many, the disk florets don’t often set seed, so they're effectively male, but they need to keep their female parts because it’s the stigma that pushes pollen out of the floret as the style elongates.  In thistles all the florets are of one kind, and they’re hermaphrodite.
Back to the rugby: I don’t know who to support.  Like most people of British origin, I have Scottish (Garnock, Ferguson), English (Collins, Hampson, Wood), Irish (McArdle, Dowdall), and Welsh (Jones, Evans, Deveson) ancestors.  Most years there are more thistles and shamrocks than roses or leeks in my garden, so I think I’d prefer Scotland to win.

Friday, 23 September 2011

Plants of the rugby world cup 3.—the rose

England, my England!  Roses, the wars of the roses, the English rose.  Roses are part of the history and culture of England and the English-speaking colonies, and their symbolic importance goes a long way back in time.

Wild roses, like this sweet briar (Rosa rubiginosa) in Canterbury, don't look much like the cultivated roses in most people's gardens.  Why not?

A flower is a specialized branch, with four kinds of leaves: sepals, petals, stamens, and carpels.  How they develop is governed by a set of floral homeotic genes.  If one of these genes is non-functional due to a mutation, some of the kinds of floral leaves don't develop properly, or they develop into the wrong kind of leaf.  Many cultivated roses have their stamens converted into petals, so instead of five petals like the flower above, they have lots, and they don't produce pollen.  Plants with flowers like those, called double flowers, tend not to reproduce, so the mutant form of the floral homeotic gene tends not to survive in wild populations, but it is successful in cultivation because the extra petals add to the showiness of the flowers.  Gardeners select these sterile mutants and propagate them.  Carnations are a similar cultivated double form derived from wild pinks.

The rose family has a huge diversity of fruits.  Think rosehips, apples, strawberries, raspberries, plums and cherries, and the dry fruits of Spiraea and Acaena.  These fruits are all made of the same building blocks, but they differ in which parts are fleshy, how many carpels are in each flower, whether they're joined or separate, and whether the carpels open to release the seeds or not.

England should comfortably beat Georgia tomorrow, but then they face Scotland.  Again, history is important: Prestonpans, Culloden.  Why is it that geographic proximity seems to cause the most intense rivalry?

Saturday, 17 September 2011

Plants of the Rugby World Cup 2.—the shamrock.

There's always a lot of debate about what is, and what is not, the true shamrock.  The stylised version looks a lot like an Oxalis and I've heard people claim the shamrock is an Oxalis.  But when I visited my cousin in County Cork years ago, the shamrock she showed me was Trifolium dubium, a little yellow clover.  This, she told me, is the plant folks wear on St Patrick's Day in Rosscarbery, Skibbereen, and Cork.
Shamrock, Trifolium dubium
Sorry about my scrappy photo.  Wikipedia, on the other hand, tells us the shamrock is the white clover, Trifolium repens:
Trifolium repens.
Whichever species is the true shamrock, it's a three-leaved (leafletted) clover, not a four-leaved.  The luck of the Irish doesn't need four-leaved clovers, it seems.  Nothing demonstrates that better than tonight's result (Ireland 15, Australia 6).

Friday, 16 September 2011

Butterfly Creek

Today was one of those days when Wellington is hard to beat—little wind and a blue sky; the harbour was glassy and the tuis were singing.  I took a group of students on a not-for-credit field trip to Butterfly Creek, just for the fun of it.

Here are some of the photos.

Hen and chickens fern, Asplenium bulbiferum.  The "chickens" are asexual reproduction additional to the spores that form beneath the leaf, which are part of the sexual cycle.

Tawa (Beilschmiedia tawa) isn't very common, mostly occurring on the more fertile soils of the valley floor

Bracket fungi basidiomata on a fallen log

Clematis paniculata male

Clematis paniculata male

Juvenile leaves of kahikatea (Dacrycarpus dacrydioides).

Sundew (Drosera auriculata)

Fern gametophytes on a clay bank

Kiekie, Freycinettia banksii.

Kidney fern, Hymenophyllum nephrophyllum.

Rewarewa seedling (Knightia excelsa)
The view over Eastbourne and the Wellington Harbour entrance from the beech forest on the Muritai Track.

A spider orchid Nematoceras trilobum.

A spider orchid Nematoceras trilobum.

Pole stand of regenerating black beech, Nothofagus solandri.

Crown of a nikau, Rhopalostylis sapida.

Liverworts with sporophytes releasing brown spores.

Monday, 12 September 2011

Plants of the Rugby World Cup 1.—the wattle.

Golden wattle, Acacia pycnantha (Wikipedia commons)
The green and gold of Australia’s sporting uniforms symbolise the wattle, national floral emblem and the biggest plant genus in Australia—a real aussie icon.  In springtime the air is scented with their blossoms.
Wattle is the common name of the genus, immortalised in the Monty Python Bruce sketch: “This here’s the wattle, the emblem of our land.  You can stick it in a bottle, you can hold it in your hand.”  The tree is known to Australians simply as wattle, but it’s the scientific name, Acacia, that has been controversial lately.  The moral of the story that follows (and this is a very brief and rather superficial account) is that the names we use for plants may be important, but the plants stay the same when the names change.  A sub-plot is that people have strong emotional attachments to names and can become quite irrational in their efforts to protect familiar names from change.
The International Code of Botanical Nomenclature (ICBN) is the rule book for applying scientific names to plants.  One of its founding principles is the type principle.  Type specimens are the reference samples for the application of names.  If you and I disagree over an identification of a sample, we can consult the type specimens and see which one our sample matches.  Or if I decide a species name includes not one but two species, the one that includes the type specimen must keep the original name, while the other gets a new name, itself defined by a new type specimen. 
When Veronica linifolia (as Parahebe) was divided, the type specimen determined that the original name stayed with the northern species (left), while the southern one got a new name (now V. colostylis)
This rule is a simple way to make a decision that all can agree with.  It saves arguments, and especially prevents authority figures, commercial or political interests, or overwhelming numbers from dominating the results.  Sometimes though, the results are inconvenient.  
The same thing applies at genus rank, so when the genus Acacia was first described, the African species A. nilotica was deemed to be the type.  Over the years, more than a thousand species had been added to Acacia, including about a thousand from Australia alone.  Then, in the 1980s, botanists started to realise that this huge genus wasn’t a natural group of related species, and it became clear the Australian species weren’t closely enough related to the African A. nilotica group to be allowed to remain in the same genus.  Under the ICBN, the African group should retain the name Acacia, while the oldest genus name that could be applied to the Australian group was Racosperma.  
However, by the late 1980s, a group of botanists concerned more with stability of names than with the principle of objective decision-making had brought a significant change to the International Code, by a vote at the Berlin International Botanical Congress.  From 1986 it has been possible to apply to an international committee to conserve a name with a new type.  This meant that there was a chance to overturn the system and keep the popular or established usage of a name that would otherwise change, by over-riding the strict application of the type principle.
Australian botanists, or at least some of them, took advantage of this and, in Vienna at the International Botanical Congress in 2005, they won the conservation of Acacia with a new, Australian, type species.  The congress was deluged with lobbying emails and faxes in support, from Australian politicians, growers, sports-people and the like.  On the other side, some accused the Australians of racism for trying to force a name change on African botanists.  One Australian email struck me for its sheer illogicality.  This asserted that the name Acacia should stay with the Australian species because Aussie sports teams compete in green and gold symbolising the wattle, as if the change of scientific name somehow meant they’d have to start wearing all black.  
As a result of the Vienna Congress’s decision, the Africans have had to change the names they use instead, and Acacia now applies to the Australian plant group.  That decision was controversial for various reasons and it came up again at the recent Congress in Melbourne, where it was approved yet again.  This was definitely a win for Australia, in accordance with the ICBN.  We botanists must follow it, whether we like it or not (and for the record, I don't).
Really though, the wattles will still smell as sweet whatever their name, and the Aussies will still be New Zealand's great rivals on the rugby field, whether they turn out in green & gold, all black, or pink.

Thursday, 8 September 2011


Spring flowers are appearing all over Wellington, all the usual sorts: daffodils, Prunus, snowdrops.  But there are a few rare treats too, like Michelia yunnanensis.  I saw these two bushes in the Botanic Gardens near the duckpond, with their white petals, dark leaves, and rusty buds.

Side-on, the flowers show the long floral axis typical of magnolias and their relatives, with spiraled flower parts.  The many separate small carpels will each develop into a one-seeded fruit.
Pink Magnolia campbellii is flowering now, and I saw a magnificent M. stellata today in Kelburn.  Sadly, I think our garden is probably too windy for these fragile flowers.