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.

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, 353–363
http://dx.doi.org/10.1071/SB12014

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.

A new classification for the southern beeches.

In New Zealand, the forest we typically identify with—the “bush”— is the lowland mixed conifer-angiosperm forest, with a canopy usually of angiosperm trees like tawa (Beilschmiedia tawa) or kamahi (Weinmannia racemosa) and large emergent conifers of the southern families Podocarpaceae (e.g., rimu, Dacrydium cupressinum) and Araucariaceae (i.e., kauri, Agathis australis).  But in most montane parts of the South Island (Te Wai Pounamu) and on often drier ridges and hill country of the North Island (Te Ika A Māui), a very different type of forest is dominant.  This forest comprises a uniform canopy of often a single species of southern beech.  Usually the forest doesn’t have a dense understory, giving an open and well-lit appearance to the interior.  This is just as much an iconic New Zealand forest as the “bush”, and one that’s familiar to many trampers.

Southern beech forest, Orongorongo Valley, near Wellington

Similar forests are found in the southern part of South America, so that travelers there from New Zealand often feel it’s just like home.  Southern beech forest also occurs in Australia, New Guinea and New Caledonia.  It’s known from fossils in Antarctica too, going back to the Cretaceous, as well as in many of the places where it still occurs today.

The southern beeches were originally classified in the genus Fagus, along with their northern namesakes, but by 1850 their differences had been recognised and they were transferred to the genus Nothofagus (the name means southern beech [correction, 21 Nov 2013: it means "false beech"; southern beech would be Notofagus.  H/T Rosi]).  As Nothofagus, the southern beeches have been important trees in New Zealand ecology, conservation, forestry, and biogeography.  Whole books have been written about them.  Nothofagus is currently reckoned to have about 40 species.  In 1962, a Russian botanist, Lyudmila Kuprianova, went a step further and proposed a new family, Nothofagaceae, for the southern beeches.  This took rather a while to be accepted.

Many botanists have wrestled with the relationships of the species within Nothofagus, using sometimes single or few characteristics, other times multiple ones.  The advents of (1) cladistic thinking (using explicit evolutionary trees) and (2) molecular characteristics from DNA sequencing have been of major help to this enterprise, because DNA has provided a wealth of new characters that are independent of the morphological ones and because the analysis and interpretation are out in the open for everyone to evaluate.  Pretty quickly, the understanding of relationships in the southern beeches has converged on a single well-supported arrangement, which was arranged into a classification by Australian botanists Bob Hill and Jenny Read, who recognised one genus (Nothofagus) with four subgenera.

Southern beech forest near Eastbourne, Wellington.

Beyond the southern beeches, DNA sequence data were also telling us a lot about the relationships of southern beeches to the oaks, beeches, chestnuts and she-oaks and it became pretty clear that Kuprianova was correct in isolating them in their own family.  It turns out that the ancestor of the beech order (Order Fagales) first divided into two species: one that was the common ancestor of the northern sweet chestnuts, beeches & oaks, she-oaks, myrtles, and more—seven families in all—and the other that was the common ancestor of just Nothofagus.  If you were to divide Fagales into two suborders, one would have seven families and many genera, the other would have just one family, and that family would have just one genus.  Thus Nothofagus and Nothofagaceae have different ranks (their place in the hierarchical classification) but identical circumscriptions (the species they contain); that redundancy means we're not using the available hierarchy of ranks to full advantage.

What’s more, the current classification of all the southern beeches in one genus Nothofagus can be a bit misleading.  Most biologists agree that it’s absolutely essential that every genus or family should contain closest relatives.  In other words, a species shouldn’t be more closely related to a member of another genus than it is to a species that’s classified in its own genus.  Nothofagus doesn’t break that rule: every species of Nothofagus is more closely related to every other species than it is to any species that’s not placed in Nothofagus.  So far, so good.

But it’s easy to assume that our New Zealand species—black, hard, red, mountain and silver beeches—might be each other’s nearest relatives, and often people are surprised to find that’s not the case.  In fact, hard, black, mountain, and red beeches are related, but silver beech’s nearest relative is in Australia.  Wouldn’t it be better if their classification and their scientific names could reflect that?

This week two New Zealand botanists, Peter Heenan and Rob Smissen from Landcare Research, have revisited the classification of the southern beeches (Heenan & Smissen 2013).  They brought together everything that’s been published so far, from both morphology and molecular systematics, and added some new data and analyses of their own.  Their findings are pretty much the same as several previous reports, but they can now place greater levels of confidence in the groups they recognise.  They comprehensively discuss alternative classifications and alternative criteria and come down with what I think is the most sensible classification. 

Nothfagaceae now contains four genera.

• Nothofagus comprises just five species from temperate South America.  The rest of the family is no longer classified as Nothofagus.
• Lophozonia is a reinstated genus, containing seven species from South America, New Zealand, and Australia.  
• Fuscospora has six species and a very similar distribution; it’s a newly recognised genus, although like the others it has been treated as a subgenus in the past.  Additionally in Fuscospora, this paper promotes mountain beech to species rank as F. cliffortioides.  I look forward to reading the evidence for that change, because it was previously treated just as a variety of black beech.
• Finally, Trisyngyne is the largest genus (25 species) and found today in the tropics: New Caledonia, Papua New Guinea and extending into Indonesia.  

These genera are strongly supported by both molecular, morphological, and chemical characteristics, and they have symbiotic fungi and parasitic fungi and insects that also seem to recognise their relationships.

Red beech, Fuscospora fusca.

Black beech, Fuscospora solandri.

Mountain beech, Fuscospora cliffortioides, near Cass, Canterbury.

Hard beech, Fuscospora truncata

Silver beech, Lophozonia menziesii.

When we use these new names for the New Zealand plants, we see immediately that we have two natural groups represented here: Fuscospora and Lophozonia.  New Zealand no longer has any species of Nothofagus.

Red beech, Fuscospora fusca, Tunnel Gully near Wellington.

A final word of a more general nature.  Some people will want to reject this change, perhaps because they feel nostalgic about the name Nothofagus, or perhaps because they feel name changes are disruptive.  But taxonomy is science and there are scientific criteria involved.  Like climate change, evolution, and vaccination, you can’t simply reject sound science because you don’t like it.  

Silver beech, Lophozonia menziesii, Haast Pass.

It’s very rare in science for there to be two equally well-supported positions such that users are free to choose whichever one they prefer.  Rather, scientists make decisions after critically considering the evidence.  It's true a classification is a human construct, but it's based on facts about evolutionary history.  Those facts are hard-won data from the field, herbarium, and genetics lab.  If your opinion contradicts those facts, then you're at risk of denying the science.

In this case however, both the old classification and the new one do pass the most important test, that of classifying related species together, so we can't rule out one or the other on that ground.  The question here is, "what's the appropriate rank for these four well-supported groups?"  But is one answer better than the other?  Heenan and Smissen argue strongly and in detail that there are good reasons to prefer their new scheme over the old one.  For instance, they show that the newly-recognised genera are at least as old, diverse, and distinct as established genera in the other families of the order, that the new names are more informative about relationships among the southern beeches, and that a redundant grouping has now been eliminated.  They conclude, and I agree, that these benefits far outweigh the temporary disruption of having new names to learn.

An Australian beech, Lophozonia moorei, growing at Eastwoodhill.

Heenan, P.B.; Smissen, R.D. (2013). Revised circumscription of Nothofagus and recognition of the segregate genera Fuscospora, Lophozonia, and Trisyngyne (Nothofagaceae) Phytotaxa, 146 DOI: 10.11646/phytotaxa.146.1.1

New associations good and bad.

The word weed can be a hard one to define.  Most people accept that a weed is a plant growing where it’s unwanted, something that’s in the way, or that stops the flower or crop you’re trying to grow from growing, or interferes with valued native vegetation.  When you think about it that way, it’s clear that one person’s crop or wildflower can easily be, or become, another’s weed.  Unfortunately, the corollary is that one person’s pest might be another’s treasure.

Ngaio, Myoporum laetum.

Last week I wrote about the common confusion between New Zealand and Tasmanian ngaio, and how in New Zealand the latter is sometimes planted unintentionally in place of the former.  Our native ngaio, although prone to self-seeding in gardens and capable of fast growth, is never really a weed here.  But it is a pest plant in California, along with some others of our native flora, like pōhutukawa and cabbage trees.  This is the story of the rise and fall of ngaio in California, as told in a recent research paper by Jon Sullivan of Lincoln University (Sullivan 2013).

Ngaio was introduced into California as an ornamental tree and widely planted around the middle of last century, mostly using a California-derived cultivar, M. laetum ‘Carsonii’. It’s the 18th most common street tree in San Francisco and is valued for its fast growth and salt tolerance near the sea.  From widespread plantings in Southern California, ngaio has spread into many wild and semi-wild communities from Sonoma County southwards to Baja California in Mexico.  It forms a dense canopy that shades out other plants and the dry woody centres of the trees are considered a fire risk.  The trees even re-sprout after fire or herbicide spray treatment, so they’re hard to get rid of.

The core of Sullivan’s paper describes the effects of the chance introduction of a tiny insect, a kind of thrips (the singular and plural are both thrips).  This thrips, Klambothrips myopori,  feeds on the leaves and shoots of plants of Myoporum and seems to have got there from Australia, where New Zealand ngaio isn't native, but where other species of Myoporum are.  Although it was first described and named from Californian collections, later a small population was discovered on boobialla in Tasmania.  And its closest relative is also in Australia, so it’s likely the insect is a dinkum Aussie and a newcomer to California.  Most likely, Myoporum thrips got accidentally introduced to California, maybe via the airline routes that converge on Los Angeles.  It probably wouldn’t have become established there, except that there were already large populations of planted and weedy ngaio for it to feed upon.  

And it got stuck in.  It's taken it about five years to kill about half the ngaios in Southern California, and the remaining live ones are looking pretty sick.

Thrips are small slender insects with fringed wings.  They mostly feed on plant sap, which they do through mouth-parts that are modified for piercing plant tissue.  A thrips infestation typically produces silvery or bronze patches on shoots and leaves, where sap has been drawn out of the cells.  Affected young ngaio shoots turn brown and the leaves are distorted.  Sullivan found high densities of nymphs and adults on affected trees in California. Other thrips are pollen feeders and are often seen in flowers, where some botanists believe they can be significant pollinators.

This inadvertent spread of thrips to California is an excellent outcome for environmental managers trying to deal with the Californian ngaio outbreak.  To introduce a biological control agent these days involves a paper war of bureaucracy, and rightly so, because they can have unintended consequences.  But in California, nature—or at least accident—had already done the job.  So, all good, you might say.

The success of Myoporum thrips in California seems to support an idea that ecologists call the New Associations Hypothesis.  The idea is that when a host-specialised organism—like a thrips that feeds only on Myoporum—comes into contact with a naive host, one that hasn’t been exposed to it before, then all hell breaks loose (for the host).  The best-known historical examples are probably the human populations that hadn’t ever been exposed to European diseases, like smallpox and measles.  Because long-distance dispersal to islands is a filter that only some organisms get through, it might be that our ngaio and other native plants have evolved in New Zealand without some or all of the parasites and predators that would damage them in their countries of origin.  If they’ve let their guard down, so to speak, then introduction of those parasites and predators by human activity could be a disaster for them.

So, what if this thrips ever makes its way to New Zealand?  We now know it can and will happily eat ngaio, and we know it has the potential to hitch rides in aircraft.  It’s yet another pest we need to watch for at the border.  Presumably in Australia, the thrips and the Myoporum have evolved together and the plants have enough defenses not to be wiped out.  But we can see what might happen here by looking at Hawai'i.  There, the Myoporum thrips has already been introduced, again probably unintentionally and perhaps from California, and it’s taken to their native species of Myoporum, M. sandwicense, with gusto.

A branch of boobialla, M. insulare.

If that calamity happens here, we can only hope the thrips prefer the introduced boobialla or Tasmanian ngaio (M. insulare) to our native ngaio, M. laetum.  My guess, and Sullivan’s too, is it’s more likely to be the other way round, because boobialla is likely to have more tolerance to thrips.  Add that to people planting the wrong species, and in the future we might find our ngaio replaced by boobialla almost everywhere.

Sullivan, Jon J. (2013-08-24) Inadvertent biological control: an Australian thrips killing an invasive New Zealand tree in California. . DOI: 10.1007/s10530-013-0532-x  

The Great Veronica Hunt — part 5.

(Note: I've updated this post on 28 September, giving the name of the botanist whose advice led me to these two Veronicas and whose collections in New Zealand herbaria verify those discoveries.  The changes are underlined.)
 
If you've been paying attention, and I'm sure you have, you'll notice I haven't posted the Great Veronica Hunt part 4, but that's what I should have called this post a couple of weeks ago.  So, skipping part 4, here's part 5.

In part 1, I described trying to find Veronica peregrina last year.  That was frustrating, because although I had a very accurate description of the location and the habitat, I was there too late in the season. To make it worse, the original collector—Whanganui botanist Colin Ogle— hadn't seen it there for a few years and doubted it would still be present.  Still, Colin had told me last autumn of a site for another species I need to photograph, V. chamaedrys, so yesterday I went after them both.

Veronica peregrina plants, Kakariki.

It took a while to find V. peregrina, but it is still there.  It was growing in silty gravel at the edges of dried up puddles in a rough vehicle track.  The biggest plants were about 75 mm tall, and the small white flowers weren't fully open on a rather dull day.  I brought some plants back to photograph, some to grow, and some to make a couple of herbarium specimens.

Veronica peregrina

This is an American plant, and it seems to be often associated with railways in the States, so it's interesting that this site is right beside the main trunk railway, at Kakariki, near Marton.  I don't know whether the activities of railways spread seeds around or whether they create suitable habitats, or maybe it's just a coincidence.

V. peregrina plants are bright green and either have no hairs or very few long glandular ones.  Their flowers are pure white, an unusual colour for a northern hemisphere Veronica (most are blue), but a common colour among our native species (only a few of which are blue).

While at Kakariki, I'd promised a colleague I'd look for spore-bearing cones on Equisetum arvense, which is naturalised along the banks of the Rangitikei River.  I'd seen it there in abundance last trip, so I confidently went down to the river.  However the river banks have been extensively sprayed, and, while it hasn't completely cleared the infestation, it's knocked it back pretty severely.  Eventually I managed to find a single cone, and took photographs and a specimen.

Equisetum arvense

Equisetum (horsetail) is an odd plant, now known to belong among the ferns. The cones produce not seeds, but spores (pine cones produce spores too: male cones make male spores that develop into multicellular pollen grains before they're dispersed, and in the familiar female cones the spores are retained, develop there, and after fertilisation each develops into parts of a seed).  Horsetail spores are formed in cylindrical sporangia underneath the hexagonal umbrella-like scales on the cone, which spread apart to release them.

Equisetum arvense, spore-bearing cone.

Then it was on to Marton for lunch and through Whanganui to the hill country inland from Kaiiwi. Colin Ogle had told me of a locality for Veronica chamaedrys, a plant I'd seen and photographed in England and France, but one that's naturalised in a few scattered localities in New Zealand.

Veronica chamaedrys,  St. Léon sur Vézère, Dordogne, France.

Here in the bush it grows around the edges of a small clearing in an old waterworks reserve.  How it got here is anyone's guess, but it's well-established in a small area.  We were too early for flowers, but it's a vigorous plant and I'm sure we can grow it on at home in a semi-shaded spot.  If this works, I'll post photos later.

Veronica chamaedrys at the edge of the clearing

The roadside cliffs through the bush were covered in flowering plants of Ourisia macrophylla subsp. macrophylla, and some of them were pink-flowered, at least in the bud.  I'd never seen such colour in New Zealand Ourisia, but in South America there are both red- and pink-flowered members of this genus.

Pink Ourisia.

It's always odd going back to Whanganui.  That's where we first settled when we emigrated to New Zealand in 1955.  I started school there (this is me on the left end of the middle row), and we used to swim at Kaiiwi Beach.

Wednesday wildflower: Veronica hederifolia

Last week I was at Lincoln, near Christchurch, working in the herbarium at Landcare Research.  I was checking my descriptions and identifying specimens towards my Veronica treatment for the new on line Flora of New Zealand, the eFlora.

Veronica hederifolia growing at the foot of an oak tree in the Liffey Domain, Lincoln.

One of the introduced species (there are about 20 of them) that I hadn't yet seen grows right there in Lincoln, so it seemed a good opportunity for a field trip to collect and photograph it.  Veronica hederifolia plants are soft annual herbs that creep along the ground.  Their flowers appear to be solitary in the axils of the upper leaves, but that depends on an interpretation.  Leaves that don't produce flowers are opposite, but there's a shift to alternate leaves, each of which has a flower in its axil.  It's probably reasonable as an alternative interpretation to consider this to be the initiation of a terminal inflorescence. In any case the leaf form doesn't change, whereas in many Veronica the flowers are produced in the axils of much smaller and simpler leaves, which are designated as bracts.

Veronica hederifolia growth form.

V. hederifolia has been growing there in Lincoln along the banks of the L2 river for over 50 years.  The botanist who collected it last—in 1985—was able to tell me exactly where to look, and there it was. There's one other collection in Landcare's herbarium, from St Mary's College grounds in Christchurch, and the Flora refers to other verified locations in Hawke's Bay, Manawatu, and Southland.

Although V. hederifolia looks a bit like V. persica in the way it grows, there are a lot of clear differences.  The leaf shape for one, but also the flowers are smaller, and the anthers are held right against the stigma so it self-pollinates, in spite of producing lots of nectar.  The fruits of V. hederifolia are hairless, circular, and barely notched, whereas fruits of V. persica are hairy along the edges of two widely diverging lobes.

Veronica hederifolia flower.

The calyx lobes are folded length-wise and have long hairs along their edges.

Veronica hederifolia, calyx.

I've taken a few small plants to try to grow it on at home, but annuals can be hard to transplant, so I'm hoping fruits and seeds will be ready when I go back to Lincoln next month.  Then I'll be able to finish my description by describing fruits and seeds and bring home some seeds to grow in the garden.

Wednesday wildflower: Cape weed

Here's something to watch for if you like foraging for wild food: be very careful about misidentifications.  I remember visiting someone in Christchurch once who was carefully transplanting wild hemlock (this one) seedlings into her herb garden, thinking they were angelica.  Well, I shouldn't be smug about that, because yesterday I made a mistake that could have had nasty consequences if I'd been foraging and if the mistake had been in the reverse direction, but I like to think I wouldn't have made it if I'd had a fresh plant or a dried specimen, rather than a photo, to identify.

It was on the Naturewatch website, and someone had posted a photo with a request for identification.  I thought it looked like puha (Sonchus oleraceus), but then I changed my mind and identified it as Cape weed, Arctotheca calendula.  The great thing about Naturewatch is that the identifications are crowd-sourced, and others quickly challenged my identification and convinced me, with evidence, that I was wrong.  The plant was indeed puha (Sonchus oleraceus).  (It's a bit embarrassing, because I wrote the Flora of New Zealand treatment for both these plants.)

So yesterday, I went looking for some fresh material.  Here are the upper surfaces of the leaves:

Cape weed (left) and puha, upper surfaces (scale=1cm)

And here are the lower surfaces.

Cape weed (left) and puha, lower surfaces (scale=1cm)

The Cape weed has more leaflets, a rounded, rather than triangular terminal leaflet, bristly hairs on the upper surface and a dense silvery mat of hairs below (puha leaves are hairless except for bristles at the tips of the teeth on the upper leaves).  Cape weed's leaf stalk is also bristly compared to the smooth puha.

Of course, it'd be hard to confuse them in flower, but early growth is often the time when foragers collect, because some plants get bitter when they run to flower.

Cape weed (left) and puha in flower.

Cape weed is poisonous, but not very, whereas puha is edible.  Check out Johanna Knox's foraging website for information, and always be sure you identify your target.

The moral of the story is that identifying plants from photos can be difficult.  Often the diagnostic characteristics can't be seen and sometimes the colours recorded in a photo don't look the same as in life.  Plant taxonomists (specialists in the classification, naming, identification, and evolution of plants) often refuse to identify photos, but I believe that so long as people understand the pitfalls it's worth having a try.  I really like the Naturewatch site, because it's self-correcting, democratic (everyone can have a go), and we all learn something from participating.

Wednesday wildflower: winter heliotrope

Winter heliotrope isn't a true heliotrope, but a daisy, related to the senecios I've featured in a few other entries in this series (here and here).  But it is both a wildflower and a weed, a garden plant that has escaped.

Winter heliotrope, Petasites fragrans.

This patch was in Aro Valley, an old-established part of Wellington, originally working class but now a mix of gentrified old cottages and student flats, arty cafes and boutiques.  The plants were in a garden that had a rather wild appearance; I'm sure its owner was deliberately aiming for a wilderness look.

Winter heliotrope flower heads.

The flowers are pink, instead of the usual yellow for this tribe of daisies (Tribe Senecioneae, characterised by the involucral bracts being in a single row, not in overlapping rows like roof shingles).  Winter heliotrope is dioecious (has separate male and female plants), but all the plants in New Zealand are males.  Their outer ray florets are all sterile (they make neither pollen nor seeds); ray florets are female in most daisies (the general structure of daisy flower heads is explained here).  The inner disk florets are male (often hermaphrodite in other daisies).  Not being able to have sex doesn't deter this plant a bit, because it is able to spread vegetatively, and of course people deliberately and inadvertently help that process.

You might note the stigmas in these florets, the large white somewhat feathery things poking through the tube of purple anthers in the centre of these florets.  How come male florets have such a large stigma?  In this and several other families, the pollen is presented on the stigma, so even though the florets are male, they still need well-developed female parts for pollen dissemination.  In a hermaphrodite daisy floret, the stigma opens after the pollen has gone to expose the two receptive surfaces.  I didn't examine these closely at the time, but in the photo I can't see any that have opened.

Wednesday wildflower: Red carpet, brown carpet

When I use the term wildflower, it's often to avoid the judgmental term "weed".  I like most plants, and if other people have species they don't like, well, that doesn't necessarily stop me enjoying them.  Furthermore, plants we designate as weeds are often biologically very interesting.  To a botanist, the term "weediness" has an ecological meaning that signifies more than a nuisance plant.

Pōhutukawa flowers

One of the interesting things weeds do well is reproduce.  All that any plant or animal needs to do is to reproduce itself at least once, but because an outcrossing sexual plant or animal contributes only one of its two sets of genes to each offspring it must do it twice to break even.  Even then, reproducing a few times doesn't guarantee the survival of all your genetic material, because which copies of genes get into a sperm or egg is random.  But some plants seem to reproduce in overdrive.

Weeds often succeed because they out-reproduce other plants.  Some are long-lived and may spread vegetatively, but others produce huge numbers of seeds.

A few red stamens have accumulated in the gutter beneath these trees, but sometimes, if it's not windy, a thick red carpet can build up.

Today's wildflower is a weed in the biological sense, but to New Zealanders it's a much-loved native flowering tree, the pōhutukawa, Metrosideros excelsa.  Pōhutukawa puts a lot of effort into reproduction, and that's probably why it's an unwanted weed in some other parts of the world where it has been introduced as an ornamental, like South Africa and Hawai'i.  Some people also consider it a weed in parts of New Zealand that are outside of its native range, such as Wellington, because it's invasive and aggressive there too.

A cluster of pōhutukawa flowers; each individual flower has about 25 red stamens (with yellow anthers) and one red style.

Pōhutukawa reproduction seems wasteful.  The trees flower profusely around Christmas time in New Zealand and in the later part of each flower's life the bright red stamens fall to the ground where they can form a thick red carpet.  This isn't over-production particularly; it's just that the red stamens are so visible and there are so many flowers producing them.  They can be dispensed with once their pollen has been dispersed.  They're visible for a good reason: pōhutukawa is primarily pollinated by birds (tūī, bellbirds, but also silvereyes and starlings) and the red colour attracts them because birds see well in the red wavelengths.

A bit later in the summer, many of the old flowers themselves fall.  I guess these are flowers that aren't setting seed; they no longer have a function and the plant can discard them.  I don't know whether these are functionally male flowers or simply flowers that didn't get pollinated, but these form a pale grey-green carpet for a time.

Pōhutukawa seeds in the gutter, Kelburn, Wellington

The third big dump of reproductive material is happening about now in Wellington, and that's the dispersal of seeds in their millions.  Most of these are never going to germinate.  They pile up in gutters, on footpaths, and at the bases of walls.  I'd like to do a rough calculation of the weight of stamens, aborted flowers, and seeds produced by a large pōhutukawa tree in a season; I think we'd all be surprised.  Multiply that, whatever it is, by the number of trees in Wellington and that's a lot of biomass falling to the ground each year.

Pōhutukawa seeds.

This prodigious reproductive effort is one of the attributes that makes pōhutukawa such a successful plant, and it's a trait normally associated with weediness.  No wonder then that our Christmas tree has become a pest in places.