Wednesday wildflower: miner's lettuce

Claytonia perfoliata, basal leaves

Miner's lettuce, Claytonia perfoliata, is wild foragers' fare.  Its succulent leaves can be lightly steamed or eaten fresh in a salad.  The plants are annual, and I first noticed the seedlings about 6 weeks ago.  Lately there have been a few early flowers.

The little white flowers form in clusters in the centre of roughly circular bracts.  Each flower has two sepals, five petals, five stamens, and three stigmas on top of the ovary.  The flower stalks elongate as the flowers get older.  The seeds are small, shiny, and black.

Claytonia perfoliata.  Basal leaves, A, adaxial, B. abaxial; C. perfoliate bract with flowers; D inflorescence and side view of flowers, showing the paired sepals.

The genetic revolution in classification has affected few plants more than it's affected miner's lettuce and its relatives.  It used to be classified with Portulaca in the Portulacaceae.  It was a big surprise to discover that the cactus family arose within that lineage, and this brought about the suggestion that the two families should be combined.  However, more recently, an alternative has been proposed: the Portulacaceae can be broken up into a number of smaller families that can sit alongside Cactaceae.  One of these is the now very much smaller version of Portulacaceae (New Zealand has a couple of naturalised species of Portulaca), but miner's lettuce and some other naturalised and native New Zealand plants ended up in the Montiaceae.  I'll certainly cover Calandrinia menziesii and Montia fontana as future Wednesday Wildflowers if I get suitable material, but for now here are some native species in Montiaceae.

Montia australasica, a common and variable alpine species found in New Zealand and Australia, at Rastus Burn, Remarkables Range, Otago.  Some botanists prefer to divide it into at least 7 species.

Montia fontana subsp. fontana is a native aquatic, here growing in a stream at Sandy Bay, Enderby Island.  M. fontana subsp. chondrosperma seems introduced, and grows on soil.

Hectorella caespitosa, here at Rastus Burn, Remarkables Range, Otago, used to be classified with its close relative Lyallia kerguelenensis (from Kerguelen Island) in its own family, Hectorellaceae.  Now their relationships are better known, they're placed in Montiaceae.  Some argue the two should be in the same genus (Lyallia caespitosa would then be the name for our species).

Going through the motions: what did moa eat?

Moa were giant flightless birds found in New Zealand (the plural of moa is moa, because the Māori language doesn’t distinguish singular from plural nouns, with one exception).  There were 6 genera and 9 species of moa; the largest, Dinornis, stood well over 2m tall.  They’ve been extinct since shortly after Māori arrived here.  It’s thought they were an easily harvested source of protein and were quickly driven to extinction.  Although everywhere on earth where humans live has extinct megafauna (e.g., aurochs in Europe, giant sloths in South America, giant lizards and kangaroos in Australia), in most places the extinctions happened so long ago that they're very hard to study.  But in New Zealand, the extinction of moa is quite recent, dating from around the 13th century, and there are still traces to be found and studied.  Deposits of regurgitated gizzard stones are sometimes found, and subfossil birds can be recovered from caves.  It's thought that some large trees still alive today might have been dispersed as seeds by moa.  

About 35 years ago, Michael Greenwood and Ian Atkinson (Greenwood & Atkinson 1977) proposed that moa could have been a major influence on growth forms of New Zealand plants.  In particular, they suggested the twiggy wiry tangled small-leaved growth forms that we call divaricating shrubs could have evolved as a defense against moa browsing.  That’s been a very popular and appealing idea, but one that’s had its critics.  While New Zealand botanists have been happy to attribute our unusual flowers to pollination by our depauperate and unspecialised pollinator fauna and our prevalence of small fleshy fruits to dispersal by frugivorous birds, many have been wary of accepting the moa browse hypothesis.

A divaricating shrub, Coprosma cuneata, Campbell Island.

Partly their objections have arisen from concern that these ideas can’t directly be tested, because moa are no longer with us.  Nevertheless, many other purely historical ideas in biology can be tested, by indirect methods at least.  Greenwood & Atkinson’s seminal paper has spawned an industry in New Zealand ecology largely driven by questions about the likely selection pressures of moa on New Zealand plants.  One recent test of moa browsing was a cafeteria experiment (Bond et al. 2004), where two other large ratite birds—emus and ostriches—were offered related pairs of divaricating and non-divaricating plants.  The birds stripped the non-divaricating plants in short order, but had trouble pulling the springy and wiry stems of the divaricates and manipulating the twigs and small leaves in their beaks. 

Another very successful research strategy is coproecology, the gleaning of evidence from fossil droppings, coprolites.  The most recent paper (Wood et al. 2012) by the moa coproecologists has received a lot of press attention because it showed for the first time that moa fed on flowers, as well as on fruits, leaves, and twigs.

The scientists found a pile of poo just inside the entrance of a cave in the Garibaldi Range, South Island mountains.  Dried in sunshine and breezes, but protected from rain, these droppings had lain undisturbed for hundreds to thousands of years.  Taking great pains to avoid contamination, the scientists sampled 35 of the coprolites, collecting DNA to identify the species of moa as well as plant species eaten, macrofossils (seeds, leaves, etc.), microfossils (pollen grains), and measuring organic content of the dung.  They also used radiocarbon dating to estimate when the droppings were dropped.

The dung was all from one moa species, the upland moa (Megalapteryx didinus), a stout bird that stood about 1m tall at the rump.  The oldest droppings were dated from about 6,300 years ago, and the youngest from a bit less than 700 years ago, so they span a good proportion of the time from the last ice retreat to the final extinction of moa.  Interestingly, several of the droppings had identical ages and plant contents and are thought to have been deposited in the same "defecation event". 

The three methods of sampling plant remains (the authors refer to these as proxies) in the droppings—pollen, macrofossils, and DNA— were complimentary.  Of these, pollen could be contamination from outside, especially when it comes from wind-pollinated trees that flower largely out of reach of moa, like Nothofagus (southern beech) or from plants that are highly poisonous, like wind-pollinated Coriaria.  The plot below, from the paper, relates pollen abundance in the coprolites to abundance in the environment; plants above the null distribution line are the ones likely to have been part of the moas' diet.

A range of montane and subalpine plants were found, some (southern beech, buttercups, sedges, grasses and Fuchsia) in all three proxies.  The results show moa were generalists, eating pretty much everything, and they ranged across all the available habitats, as the figure below demonstrates.  

But only a few of the eaten plants might be divaricating shrubs.  These include Myrsine and Coprosma, for which the DNA and pollen evidence can't distinguish if the plants eaten were divaricating or not, and Neomyrtus, which is divaricating.

A divaricating Myrsine, M. divaricata.

A non-divaricating Coprosma, C. foetidissima.

The finding of pollen from bird-pollinated flowers—Phormium and Fuchsia—is especially interesting.  These produce quite large amounts of sweet nectar and are pollinated by birds that are much smaller than moa, such as bellbirds and tūī.  Yet their pollen is not likely to have got into coprolites other than by passing through the gut of the moa.  The authors aren't suggesting moa were pollinating the flowers, rather that they were eating them.  The large fleshy flower stalks of Phormium are probably quite nutritious and the nectar from a single flower is a small but sweet treat for a human.  On the other hand, Fuchsia flowers are produced singly or in small clusters on the twigs or bare trunks of the trees, and it must be quite finicky work to pick these one at a time; they hardly look worth the effort for a large hungry bird.  If moa had a taste for sweet nectar such that they were a threat to flowers, could their grazing have driven the evolution of tall scapes in Phormium and the tree habit in Fuchsia excorticata?  The controversy lives on.

Flowers of tree fuchsia, Fuchsia excorticata.

Flowers and young fruits of mountain flax, Phormium cookianum.

I was surprised to find in this paper evidence that moa ate so many small alpine herbs and small fruits too.  They might have been significant seed dispersers.  This, like the Fuchsia flowers, suggests they might have been capable of choosing tasty morsels.

A previous study by some of the same scientists (Wood et al. 2008) showed the presence of a small buttercup, Ceratocephala pungens, in moa coprolites from Otago.  Ceratocephala is tiny and seasonal.  The plants are ground-hugging rosettes at most a couple of centimetres across, and they grow in bare ground, yet their seeds were found in coprolites from two species of moa.  The genus is otherwise known only from Europe and W. Asia, so when this new species was described from New Zealand, I entertained the possibility that it might not be a native (Garnock-Jones 1984).  Yet here it is, in coprolites produced before humans arrived in New Zealand.

In the past, the deer-hunting lobby in New Zealand has argued that introduced mammals were good for the environment because they replace these extinct giant herbivorous birds.  This study suggests otherwise.  Two very palatable plants that were common in moa diet—Fuchsia and wineberry—are no longer found on the Garibaldi Range, and many others are now confined to inaccessible cliffs and edges of sink-holes.

References.

Bond WJ, Lee WG, Craine JM (2004). Plant structural defences against browsing birds: a legacy of New Zealand's extinct moas. Oikos 104: 500–508.

Garnock-Jones PJ (1984). Ceratocephalus pungens (Ranunculaceae): a new species from New Zealand.  New Zealand Journal of Botany 22: 135–137 (Note the different spelling in this paper; the original spelling Ceratocephala is now preferred)

Greenwood RM, Atkinson IAE (1977). Evolution of divaricating plants in New Zealand in relation to moa browsing. Proceedings of the New Zealand Ecological Society 24: 21–33.

Wood JR, Rawlence NJ, Rogers GM, Austin JJ, Worthy TH, Cooper A (2008). Coprolite deposits reveal the diet and ecology of the extinct New Zealand megaherbivore moa (Aves, Dinornithiformes).  Quaternary Science Reviews 27: 2593–2602.

Wood JR, Wilmshurst JM, Wagstaff SJ, Worthy TH, Rawlence NJ, & Cooper A (2012). High-Resolution Coproecology: Using Coprolites to Reconstruct the Habits and Habitats of New Zealand's Extinct Upland Moa (Megalapteryx didinus). PloS one, 7 (6) PMID: 22768206

Some plants from Shotover Saddle

Last week I went to Shotover Saddle in West Otago with Dr Heidi Meudt (Museum of New Zealand botanist).  We were collecting samples of Veronica and Myosotis for Heidi’s research, and I was there because I’d been before and knew the route.  Heidi is investigating the relationships and evolutionary history of these plants, using some of the latest DNA-based techniques.

Looking down to the Matukituki from about 3/4 of the way up.

It’s a long slog from the West Matukituki River to the top.  We were lucky because we had a rented four wheel drive and permission from Mt Aspiring Station to use the road beyond a locked gate.  Even so it was a long and tiring day.

The view across the valley, 1300m below, to Mt Rob Roy.

The only soul we saw all day was this paraglider pilot who flew along the ridge just above us.  We were told later he'd probably taken off from Treble Cone, near Wanaka.

The saddle (a common term in New Zealand for a pass or col) is the main access from the Matukituki to the head of the Shotover River.  It’s in Mt Aspiring National Park, so all our collecting was under permit from the Department of Conservation.

Veronica planopetiolata

Our main quarry was Veronica planopetiolata, a small glossy mat-forming plant of high altitude (1750m) scree, boulder field, and rock crevices.  It’s probably common enough in the Park and nearby, but not often collected.  When I did my PhD thesis (1975) on this group of Veronica, then classified as Parahebe (and here's an explanation for the change), I tried many times to collect some of this plant, but I never saw it in the wild until 2006.  It’s interesting because it’s tetraploid (has 4 sets of chromosomes instead of the usual 2), suggesting the possibility of a hybrid origin in its distant past.

Veronica planopetiolata with pink flowers

Most of the plants had white flowers, but some were pink (this photo was taken on my previous trip).

Veronica planopetiolata, like a lot of cushion-forming veronicas, has seed capsules that open when they're wetted by rain, and the energy from falling rain-drops splashes out the seeds.  My former student Gesine Pufal showed they don't disperse very far, and she concludes it's a way to restrict dispersal in plants that grow in very small habitat patches (Pufal et al., 2010; Pufal & Garnock-Jones 2010).  

Red Rock

This is quite a common plant on the scree below Red Rock, and in rock crevices and gullies nearby.  I’d expect it to be common at higher altitudes on Mt Tyndall and beyond, but getting up there is beyond my capabilities.

Veronica thomsonii

Other veronicas in the area include a hairy cushion snow hebe, V. thomsonii, a shrubby hebe (V. subalpina), and a whipcord hebe, V. hectorii.

Veronica subalpina

Veronica hectorii

The daisy or sunflower family Asteraceae is well represented in many parts of the New Zealand mountains.  The family includes a number of large groups, each of which appears to have evolved many species from an original founder.  There were more species than I’m showing here.

The Senecio tribe was represented by Dolichoglottis scorzoneroides and Haastia sinclairii, both of which are part of the Brachyglottis radiation in New Zealand.  Both these species had ancestors that were probably shrubby daisies.

Dolichoglottis scorzoneroides

Haastia sinclairii

The Aster tribe was represented by a large number of alpine daisies of the genus Celmisia.  Many Celmisia species appear to have wide distributions, so that on any one mountain there are often a large number of different ones, compared to Veronica, which has more species, but more localised distributions.

NZ edelweiss, Leucogenes grandiceps.

The New Zealand edelweiss has very similar flower clusters to its famous European namesake, but it’s classified in a separate genus and appears to have reached its similarities independently.  There are four species.  It’s much more closely related to other New Zealand genera in the Raoulia complex.

Craspedia

This woolyhead (Craspedia) is one of a baffling group of New Zealand plants.  Such is the variation in this group that botanists think there are a few dozen species still to be described and named.  There’s a lot of work to be done before we know this group in detail, and all the tools in the botanist’s toolbag will be needed to sort out the mess.

Wahlenbergia albomarginata

Wahlenbergia albomarginata, southern bluebell is a common plant throughout New Zealand (the North Island W. pygmaea is likely to be the same species).  It was common from the river bed up to Shotover Saddle, growing in grasslands, fellfield, and rock outcrops.

Schizeilema haastii var. cyanopetalum

Schizeilema is a small genus quite closely related to the giant Stilbocarpa of the subantarctic islands.

Ourisia glandulosa

A couple of mountain foxgloves were also of interest, because this group was the subject of Heidi’s PhD and several papers since.  This one is O. glandulosa.

Veronica thomsonii (top and left) growing in a single cushion with Myosotis pulvinaris (lower and right)

We saw two Myosotis (forget-me-nots), but only were able to collect one, because the other was just a single plant.  Myosotis pulvinaris is a cushion plant that looks superficially very like Veronica thomsonii.  The Myosotis differs in its bigger leaves and some details of the form and distribution of its hairs, and of course their flowers and fruits are quite different.  New Zealand forget-me-nots mostly have white flowers or sometimes yellow ones.

Looking west from below Red Rock.

References

Pufal, Gesine; Ryan, Ken G; Garnock-Jones, Phil.  2010.  Hygrochastic capsule dehiscence in New Zealand alpine Veronica (Plantaginaceae)  American Journal of Botany 97: 1413–1423.

Pufal, Gesine; Garnock-Jones, Phil.  2010.  Hygrochastic capsule dehiscence supports safe site strategies in New Zealand alpine Veronica (Plantaginaceae). Annals of Botany (doi:10.1093/aob/mcq136, available online at www.aob.oxfordjournals.org).