Wednesday wildflower: Banksia integrifolia

Many of our most widespread New Zealand invasive plants came here as weeds, maybe as seed impurities, or in soil or agricultural products.  A majority came from Europe, where the new people came from and where climates and land use practices are similar.  Others were deliberately brought, like gorse and barberry as hedging plants.  But as people started to realise the risks of allowing invasive plants into the country, our controls have tightened, and now it's pretty hard to deliberately or accidentally get something across the border.

So where are the weeds of the future going to come from?  Many are already here, as garden plants.  Perhaps 20,000 species are cultivated as ornamentals or crops.  Many are tender and hard to grow, and it's unlikely these will escape.  But if the climate changes, some subtropical or dry-climate plants might be able to propagate and spread without human help, becoming new weeds.

An infestation of Hieracium lepidulum, near Arrowtown, Otago.

Weed naturalisation often takes a while.  There may be a period of decades when botanists find the odd few plants, but it's not certain whether full naturalisation is taking place.  But then, in some, there's a sudden increase and they quickly become common and widespread.  Hieracium spp. did this.  Maybe the slow start is caused by low genetic diversity, lack of pollinators or dispersers, or maybe there's a change in land use (irrigation, fertilisation) that suddenly suits the invader.  In some, it's possible that the establishing population might evolve (allele frequencies change in the establishing population, due to natural selection or perhaps genetic drift).

Banksia integrifolia is a weed that seems to be in this early establishment phase.  It wasn't included in the Flora of New Zealand volume that deals with naturalised "dicotyledons" (Webb et al. 1988).  I remember collecting a wild specimen on Great Barrier Island in 1990.  Whether or not that was the first wild record, nowadays this small Australian tree has been picked up in quite a few localities.  I collected my second specimen a few years ago growing just outside the predator-proof fence of the Karori Wildlife Sanctuary (now Zealandia).  The authoritative plants database of Landcare Research is the best source for plant data because it's collection based (therefore verifiable) and it incorporates the expertise of the professional taxonomists there: they record specimens of Banksia integrifolia from Northland, South Auckland, Taranaki, Manawatu, Wellington, and Nelson.

It's possible Banksia integrifolia is a new woody weed in the making, which will take off shortly and become a problem.  However it is a fire-adapted species, needing fire to split the woody seed capsules and release the seeds in large numbers, and being a tree, it should be easy to eradicate before it flowers, unless there are large numbers.  This is a plant to be viewed with caution, so a number of Wellington botanists were concerned when Zealandia planted young trees inside the sanctuary because their compact inflorescences could provide out-of-season nectar for birds like tūī, hihi, and bellbirds.

Banksia integrifolia at Zealandia

I visited Zealandia today and took these photos.  The sanctuary and the forest are doing well, even in this dry summer, and the bird life was spectacular.  The Banksia have established well, ironically quite close to a display that warns about invasive plants.  They were in flower, which is timely because the only native bird-pollinated flowers I saw were on a single rātā, Metrosideros fulgens, and that seems out of season (normally flowers early Spring).  So, it's good for the nectar-feeding birds, but let's hope the local botanists who advised Zealandia against planting Banksia were wrong about its ability to establish.  Time will tell.

An inflorescence of Banksia integrifolia

Banksia is a member of the Protea family, Proteaceae.  Its flowers are pollinated when birds are attracted to feed on the nectar that flows from small nectaries alongside the base of the ovary.  The stamens are carried on the four petals, and these curl back after the stamens have deposited their pollen on the style.  Later, usually after the pollen has been removed, the stigma expands and becomes receptive, so the style and stigma first present the pollen to visiting birds, then receive pollen in later visits.

Two flowers of Knightia excelsa, rewarewa.  Note the bands of white pollen on the club-shaped tip of the style, and the anthers now tucked away on the coiled petals at the base of the flowers. The stigma will expand at the very tip of the style, later in the life of the flower.

The native tree Knightia excelsa (rewarewa) is also a member of the Proteaceae, and also has large clusters of flowers that function in a similar way, being pollinated by native birds like tūī.

Updates.

Leon Perrie commented: "That's amazing that Banksia integrifolia isn't in the 1988 Flora IV, given that adventive populations are now so established and widespread. The New Zealand Virtual Herbarium has over 130 specimens, most of them probably of wild plants. I think this species can definitely be put in the weedy category! I've seen it spreading prolifically in the Northland 'gumlands' (along with Hakea). Also a few spots around Palmerston North."

Mike Bayly from Melbourne tells me the plants there (subsp. integrifolia) probably don't need to have a fire to open their fruits; I guess warm dry weather is enough.  He's seen unburned plants with open fruits.

These two comments indicate I underestimated its current establishment and its potential to be an aggressive weed in my post.

Reference

Webb, C.J.; Sykes, W.R.; Garnock-Jones, P.J. 1988.  Flora of New Zealand, Vol. 4.  Botany Division, DSIR, Christchurch.

The Big Dry of 2013

Wellington has been sunny and calm almost all year, with no rain in the last month.

As I write (13 March 2013), Wellington has just 20 days worth of stored water reserves.  We had a stunning Christmas Day, hot and still, with a temperature in the low 30s, and since then it's been mostly sunny, warm, and calm.  It's the best summer weather since we moved back here in 1994, although my childhood memories are of endless summers, swimming at the beach, and burnt dry lawns every year.  It's too soon to panic, because there's a chance it will rain this weekend.

The garden is coping pretty well.  I just have to water the plants in pots and things that are newly planted.

Veronica stricta suffering from drought.  This plant's roots are in a crack in a block wall, so it doesn't have access to a deep moist soil.

The hebes (Veronica spp.) are like coal mine canaries for drought in the garden.  They're the first to wilt and their normally glossy leaves lose their shine.  But give them a good soaking as soon as they start to wilt, and they'll bounce back pretty quickly.  The related speedwell hebes are similar.

A small speedwell hebe (probably a hybrid between Veronica lanceolata and V. hookeriana), originally from the Maungaharuru Range, now growing in a pot in Wellington, and suffering from the drought.

OK, it's time to water the driest plants in the garden, as frugally as I can.

More on ants and pollen

Phil Lester, the entomologist who kindly identified the ants I wrote about yesterday, has sent me some pictures of ants with Muehlenbeckia flowers, and given me permission to use them.  This is the same ant species, Monomorium antarcticum, on flowers of Muehlenbeckia complexa.

Southern ant, Monomorium antarcticum, on male Muehlenbeckia complexa (photo (c) P.J. Lester)

In the photo above there appears to be pollen caught in the hairs on the ant's head; he's walking away from a cluster of male flowers.  Here's an enlargement.

Here, another ant is on a female flower.

Southern ant, Monomorium antarcticum, on female Muehlenbeckia complexa (photo (c) P.J. Lester)

There doesn't appear to be pollen on this ant, and the flower is probably too old to pollinate; the ones above and below are more likely to have had receptive stigmas.

These photos were taken near Wellington Airport on the coast.  The plants had a major scale and mealybug infestation that was probably attracting the ants.

Ants on Parsonsia.

Southern ant with its head in a Parsonsia flower; its hairy abdomen is at the top of the picture, head (also hairy) at the bottom.

A couple of climbing plants are having a second crack at flowering right now.  Muehlenbeckia australis and Parsonsia heterophylla are both flowering again, even though the same individuals flowered heavily back in November.

Parsonsia heterophylla, Karori November 2012.

Muehlenbeckia australis, Karori, November 2012.

The Parsonsia flowers were covered in little black ants, which I didn't see in the November flowering.

It's hard enough to identify plants from photos and we don't like being asked, so I'm grateful to Professor Phil Lester for telling me this is probably Monomorium antarcticum, the southern ant. It's a common native species, or more likely a species complex.  My pictures don't show the mandibles and the segments of the antennae, which are needed for a formal identification.

Head to head, two ants probe the same flower.

It's tempting to make the assumption that these are pollinators.  There were large numbers of them, they were concentrating their attention on the flowers, probing deep into the centres of them.  But it's harder to test the idea.  You'd need to show they were carrying pollen on their bodies and transferring it effectively between flowers.  Phil Lester says he's seen Monomorium visiting flowers before, and with pollen on the hairy parts of their bodies, so they might transfer pollen between flowers, but less likely between vines.  Heine (1937) recorded several flies, including both Tachinids and Syrphids, a beetle, and several moths, but not ants, as flower visitors to Parsonsia heterophylla.  It seems likely to me that if ants are pollinators of Parsonsia they play only a minor role compared to other insects, and if they're stealing nectar they might even be counter-productive overall.

Reference.

Heine, E.M 1937.  Observations on the pollination of New Zealand flowering plants.  Transactions of the Royal Society of New Zealand 67: 133—148.