Wednesday, 31 August 2011

Bright eyes

Euphrasia is a genus of hemiparasites in the family Orobanchaceae.  In England they’re called “eyebrights” and, in most of the European species, plants are annual, like this E. nemorosa, introduced in New Zealand.
Euphrasia nemorosa, Waituna, Southland, New Zealand.
Euphrasia are called hemiparasites because they steal only water, but not food, from their hosts.  Their leaves are green, unlike the related broomrapes (Orobanche) which are pale brown holoparasites.  
Our native Euphrasias are mostly alpine.  Many are small perennial shrubs, like this E. cuneata on the Rimutaka Range.
Euphrasia cuneata, Rimutaka Range, New Zealand
Others are annuals that live in alpine boggy sites, like this E. dyeri.
Euprasia dyeri, Lammermoor Range, New Zealand
I have to show you where it was growing, among Oreobolus sedges, which it was probably parasitizing, in a string bog under a typical Otago summer sky.  The mountain range in the distance is the Rock & Pillar Range, and on the other side of it is the Maniototo plain, where Graham Sydney paints landscapes with lenticular clouds just like this one.
String bog in alpine tussock grassland, Lammermoor Range, Otago, New Zealand
Among the trends in the evolution of Euphrasia in New Zealand is a reduction in flower size, possibly associated with self-pollination, but some flowers are larger.  Two odd extremes are reached in E. wettsteiniana which grows at low altitude in Westland.  In flowers of E. wettsteiniana, there are only two seeds, one in each half of the capsule, and the corolla tube of the flower is hugely elongated.  Does this lift the flower above the water level of the swamps, raise it out of the wet grass, or is it a way to control the pollinators' behavior?
Euphrasia wettsteiniana, Kangaroo Lake, Westland, New Zealand.
In the South Island, several species, like E. dyeri and E. repens, vary from one population to another.  E. cuneata is also variable—compare the flowers of this plant on Mt Ruapehu with the Rimutaka plant above. 
Euphrasia cuneata, Mt Ruapehu, New Zealand.
Botanists' views vary about how to handle this sort of variation (and in what follows I’m talking generally and not referring to Euphrasia).  Does it mean several species are involved, or are these just local forms of single but variable species?  This is a question that’s too often not settled by applying the methods of science; rather, botanists sometimes fall back on assertion and authority.  Different appearance isn't sufficient, because there are many explanations for it besides speciation.
In my opinion, these questions need to be tested explicitly.  I think the most powerful approach is to start with the hypothesis that such populations are conspecific (i.e., they belong to the same species).  That’s a hypothesis that can be tested.  Any data that clearly falsify the hypothesis will compel us to reject it, and treat such populations as different species.  But if the evidence isn’t compelling, I advocate waiting for more data before rushing ahead with naming a new species.
What sort of data would compel us to reject such a hypothesis of conspecificity?  The data would have to be evidence that the two populations aren’t able to exchange genes, or that they haven’t exchanged genes for so long that they have diverged genetically.  If they couldn’t be crossed, or if their hybrids were sterile, that would be convincing.  Population genetic analyses might show a lack of gene flow between them.  A number of inherited independent differences between them would also be evidence they don’t cross.  Chemical, morphological, genetic, even behavioural differences can be used.  
Ecological data, such as the soil type or other aspects of the plants' habitats, don't help much with the question of how many species are involved.  Such data may tell us something about the process of speciation, but they're not powerful evidence about whether speciation has actually happened.  Many species can occupy a range of habitats and look very different as well—our own species is one of the best examples.
When different looking populations can’t be shown to be separate species, botanists can still recognise their differences using ranks that are lower than species, like subspecies, variety, and form.

Thursday, 25 August 2011

Don't judge a plant by appearances ...

... writes Ken Thompson in the Telegraph. The article provides welcome support for those of us who believe evolutionary relationships should be of prime importance to classification.  Most of the time, related plants are also look-alikes, but not always.  Look-alikes aren't necessarily related.  Those who believe plants that look just alike should be classified together are at risk of grouping unrelated similar plants.  Thompson points out that DNA data have provided a powerful new tool in this research, and that DNA is the stuff that evolves, so it's fundamental to such studies.

Thompson finishes with a comment on the recent (Garnock-Jones et al., 2007) transfer of Hebe and related genera back to Veronica, where these plants were originally placed: "So, with apologies to the many dedicated members of the Hebe Society, hebes are gone, and they aren't coming back."

That change continues to be argued.  Most professional taxonomists, like David Mabberley and the experts at Landcare Research, have accepted it, but a few taxonomists and many field botanists and ecologists in New Zealand have not.

The change to Hebe, made in the 1920s by Oliver, Cockayne & Allan, and others, reflected the differences between the New Zealand hebes and the northern hemisphere Veronicas.  We now see these changes as reflecting adaptations of Veronica to life in New Zealand, especially the hebes' woodiness, more tubular flowers, and capsules flattened in a different plane.  These adaptations made many (but by no means all) of them look different from their northern relatives. Also (and secondarily, because this was discovered after the split) they have a different chromosome number (which is now interpreted as easily derived from common Veronica chromosome numbers, i.e., no mystery).  But although they look rather different, fundamentally they have a lot in common, as studies of morphology, chemistry, cytology, and genetics show.

Other distinctive groups within Veronica have also in the past been classified as separate genera, like the Eurasian Pseudolysimachion and North American Synthyris.  The problem is that when these and the hebes are removed from Veronica, the remaining Veronicas aren't a natural group.  Many of them are more closely related to one or other of these segregates than they are to the type species of Veronica.

Here's the problem illustrated.  These three species (let's forget about their names for now) are all related, but the middle one is more closely related to the right hand one (they share a more recent common ancestor) than it is to the left hand one.  That's a statement that's well supported by molecular systematics.

Three Veronica species (the left one courtesy Wikipedia commons).  The left and middle plants are herbaceous and have blue flowers; the right one is woody and has white flowers.
Now we can rewrite that statement, replacing "left", "middle" and "right" with their previous names:  "Veronica arvensis is more closely related to Hebe elliptica than it is to Veronica officinalis".  Does that statement make you feel uncomfortable?  Note also that the left and right species are the types of Veronica and Hebe respectively.  It would make more sense to transfer V. arvensis and a couple of hundred other Veronica species to Hebe (our statement would then read: "Hebe arvensis is more closely related to Hebe elliptica than it is to Veronica officinalis"), but that would really put the cat among the pigeons.

Although Hebe as a scientific name is no longer supported, we recommend keeping it as a common name (hebe), and gardeners can use it that way with cultivar names (e.g., hebe 'Blue Gem').  Very few have a different epithet in Veronica (e.g., Hebe elliptica reverts to its original name Veronica elliptica and H. societatis is renamed V. societatis).

At a more fundamental level this discussion is about where we should place the gaps in classifications. Some say they should be placed where lineages diverge. Others say they should be placed where apparently major bursts of evolutionary change have occurred, even if those fall within lineages and separate related species.  But so many biologists are already using phylogenetic thinking and phylogenetic classifications (in ecology, biogeography, evolution, physiology, drug discovery, plant breeding) that the question is already pretty much decided.
Garnock-Jones, PJ; Albach, D; Briggs, BG 2007: Botanical names in Southern Hemisphere Veronica (Plantaginaceae): sect. Detzneria, sect. Hebe, and sect. Labatioides.  Taxon 56: 571–582.

Tuesday, 23 August 2011

You know you're in New Zealand when ...

... the Rugby World Cup being 17 days away is more important news than the overthrow of Gadhafi in Libya.

Also when most native flowers are small and green and unisexual.  Here are male (left) and female flowers of Griselinia littoralis, from separate trees in the Victoria University of Wellington grounds.

Griselinia littoralis, male flower (left) and female flower (right)

These are not to scale.  Male flowers are about 5mm diameter; females about 3mm diameter.

Monday, 22 August 2011

Pittosporum cornifolium

These orange fruits with black seeds caught my eye as I was walking up the path beside the Students' Union building.  The orange colour isn't a fleshy aril, but simply the inside of the capsule, and it serves to highlight the sticky black seeds.  Is it a mimic of other plants that present black seeds on a fleshy orange or red structure (podocarps, Alectryon, Ixerba)?  If so, it's getting its seeds dispersed for the small cost of a bit of orange pigment instead of the energy rich epimatium of a podocarp or aril of Alectryon or Ixerba.

There were tuis nearby making quite a racket, but they were disputing in a flowering P. crassifolium tree that was interleaved with a flowering puriri (Vitex lucens), so it was more likely nectar they were interested in.

The epithet cornifolium is a reference to the leaves of the dogwoods, Cornus, which are also in whorls of four.  Here's Cornus canadensis in the grounds of the University of New Brunswick, Fredericton, Canada.

Tuesday, 16 August 2011

Yellow snow.

In New Zealand, August is the month when pine pollen is dispersed on the wind.  Usually it’s best seen as a pale yellow tide mark around puddles.  But this week, we’ve had the lowest snowfall in Wellington for many years, with snow falling in the city and closing the airport for a while, and some of the snow is pale yellow with pollen.
In Karori, where I live (200 m altitude) we’ve had snow on the ground for a couple of days.  It came in three bursts, one on each of three successive days.  Although people in many parts of the world will wonder why this is even worth writing about, it’s been a source of great excitement here.  That’s because New Zealand’s climate is moderated by the surrounding oceans, and it’s rarely hot or cold.  Snow is rare at low altitudes in the North Island, and it’s 16 years since it last settled in our garden.  Here's snow falling at Victoria University of Wellington and in Kelburn, a nearby suburb.
Pollen grains are not single cells.  Pine pollen grains have four cells each at the time they’re shed.  Each is thus an independent multicellular organism, and it lives for about a year, so that this year’s pollen grains will spend the next year burrowing into the tissue of an ovule in a female cone, where one of their two sperms will fertilize an egg.  At least it will if it’s one of the very few lucky ones to be blown by chance onto the ovule of a female cone.  Otherwise, like 99.9999% of the grains, it’ll end up on the edge of a puddle, on a snow drift, or even forming a scum on the sea.
Pine pollen forming a scum at the beach, Monterosso del Mar, Italy, May 2006.

Saturday, 6 August 2011

Carnivorous plants

I want to give a bloggy shout-out to Johanna Knox, author, and Sabrina Malcolm, illustrator, of The Flytrap Snaps, the first book of a series launched this week.  It's a chapter book for young readers, with a botanical theme.  Order it for youngsters you know, and there's more information on Facebook here.

Friday, 5 August 2011

Rue the day

There are a quite a few plants called something-rue or something-bane in English.  I’m thinking of fleabane, wolf’s bane, goat’s rue, and rue.  They all suggest plants that are toxic or at least repellant, plants you'd rue, or regret, eating or touching.  I’ve seen rue (Ruta graveolens) a couple of times in the Mediterranean, usually near the coast, like this plant on the Cinque Terre trail in Liguria, Italy.
So, it was a nice surprise to see a row of rue on a roadside berm in Northland (suburb), Wellington last week.  It was planted to surround a patch of angelica (Angelica pachycarpa, not the culinary A. archangelica), maybe to keep cats and dogs away.  It’s pretty stinky stuff and the smell takes a while to wash off the hands.
Ruta graveolens, Northland, Wellington 2011.

The genus Ruta gives its name to the family Rutaceae, which includes citrus and many other plants.  Rue has traditional  medicinal uses, and can cause dermatitis.
Phebalium squameum (satinwood) is another member of the Rutaceae. The best examples I know are specimen trees in the Wellington Botanic Gardens, but usually in Wellington it's a hedge plant. It has a peppery smell and little starry white flowers. The wood is especially interesting. First, it's pale or yellowish, although often affected by boring insects and rotting of the heart wood. Secondly, it burns well because of the volatile oils that are common in the family Rutaceae (squeeze oil out of a lemon or orange peel next to a lighted match to see what I mean; video here). Thirdly, it can cause a pretty severe contact dermatitis in susceptible people. I first got this as an 8 year old when we planted a Phebalium hedge all round our section in Tawa, and it came back a few years ago when I cut up some logs for firewood. 
Satinwood trees in the Wellington Botanic Gardens.

Satinwood is an Australian tree; they have a lot of Rutaceae there, but we have only three native species.  A colleague reported getting a rash from the native mairehau, Leionema nudum.   She described blisters on her nose, fingers, and arms that lasted for weeks after she crushed and sniffed some mairehau leaves in Northland (district), where it grows.
Satinwood leaves.

It seems sunshine and moisture (sweat or water) make the dermatis worse; it’s a photosensitive dermatitis.  Grasses, parsnip tops, and especially Heracleum can also cause photosensitive dermatitis. I remember my Mum got photosensitive dermatitis on her face from using an all natural organic herbal soap. And here are my legs after tramping through long grass in flower on a sunny day in the Takitimu Range (Southland) a few years ago.