Saturday, 26 November 2011

Introducing the herbarium

A herbarium is one of the main tools for research and documentation of plant biodiversity.  It sounds like a garden, and in fact an old name for a herbarium is hortus siccus, or dried garden.

A herbarium is a collection of dried and pressed plant specimens.  The first herbarium is thought to have belonged to Luca Ghini, an Italian professor of botany, in the 16th century.  Early herbaria were kept in bound books, but mounting each specimen on a separate card—we call them "sheets"— means the specimens can be rearranged and studied separately, and it minimises damage.

The specimens are pressed only to keep them flat while they dry.  It's the drying that preserves them.  The best specimens have all the plant parts represented, so they can be studied, but this gets tricky with large plants.  With palms and tree ferns, where a single leaf can be several metres long, there are compromises to be made.  Kept dry and free of pests, a herbarium specimen can last for hundreds of years.  Several New Zealand herbaria have specimens collected on Cook's first voyage in 1769, and they're still in good condition.

The label on a herbarium sheet is very important.  It identifies the plant, tells where it was collected (now with GPS reference), what habitat it was growing in, who collected and identified it, and when, and provides notes (e.g., flower colour, abundance, scent, etc.).

The main advantage of a herbarium is it brings a large sample of different species together in one place where they can all be compared.  And it brings a large sample of individuals together too, sampled from different locations and different habitats.  While field work is important in biodiversity, the detailed research and discovery often takes place in the herbarium.  I remember sorting buttercup specimens (Ranunculus) with the late Tony Druce in the late 1970s.  We found an odd specimen in the Ranunculus hirtus folder that we thought might be an unidentified introduced plant.  Among the specimens of the next species we looked at, we found another, similar, one.  By the end of the day we had a pile of specimens of what we were now sure was an unnamed native species, now called R. altus.  It's a common plant on montane forests of the South Island, on disturbed sites like old landslides.
Ranunculus altus at Rough Creek, Arthur's Pass National Park.
We use herbarium specimens all the time in taxonomy.  Most often we use them as references to check our identifications.  In very critical cases, we can go back to the type specimens, which define the usage of a name.  We also use them when we describe species for publications.  We can even extract chemicals, including DNA, from herbarium specimens for study.

Another important role for herbaria is to document observations.  Let's say I observe red admiral butterflies pollinating Veronica stricta.  I can report that in a scientific paper, but how can the reader be sure of my identification?  If I collect a specimen of the actual plant, then even if I'm wrong it can be checked and if necessary corrected.

Modern herbarium label data are becoming databased, so that on line searches for information are increasingly possible.  Thus we can map distributions, and compare these with other information in geographic information systems.  Traditionally, herbaria have been organised taxonomically, following the scientific classification system, but databasing allows information to be assembled using other parameters, like location, habitat, flowering times, or growth forms.  If you cared, you could generate a list of dicotyledon trees growing in Canterbury above 500m altitude that flower in January.

New Zealand has three large herbaria, at Landcare Research, Te Papa, and the Auckland Museum.  There are smaller ones at other research institutes and universities.  They collaborate through the New Zealand National Herbarium Network. Overseas, there are many much bigger collections, like those at Kew, Paris, Berlin, St Louis, and New York.  The herbarium is an essential tool for studying and documenting plant diversity, and a valuable resource for its conservation.

Wonderful as they are, herbaria have their imperfections and problems, which I intend write about in future blogs.

Friday, 11 November 2011

Hayfever (allergic rhinitis) time

I love it when the spring winds die away and the warm days of summer arrive.  But I hate it too, because when Dactylis glomerata flowers, my life becomes miserable.  I'm allergic to its pollen, and a bit less so to the pollen of a bunch of other grasses and wind-pollinated trees and herbs: oaks, chenopods, and plantains.
Cocksfoot, Dactylis glomerata, Wellington, NZ.

Dactylis glomerata, or cocksfoot, is a major pasture grass and weed in New Zealand. Its pollen is abundant from early November until the first week of January (I'm a walking bioassay) and again with a minor peak in March.  In 1990, we bought a house in Okuti Valley, Banks Peninsula (this one), only to discover after we'd moved in that this valley used to be the cocksfoot seed growing centre of the known universe.  It was Hell.

My first hayfever attack happened when I was about 9 or 10.  My brother and I were playing outside with toy bombs that carried percussion caps, which exploded when you dropped them.  (Fifteen years after WW2, these military toys were still very popular.) So we both reported in with itchy eyes and the parents assumed it was to do with the gunpowder in the caps.  They called the doctor—doctors used to visit, on Saturday afternoons too, in those days— and we were sent to rest in darkened rooms.  It was some time later they realized it was hayfever.

The TV advertisements for hayfever remedies always feature showy flowers: lilies, daisies and the like.  But hayfever is an affliction caused by the insignificant flowers, the ones that are wind pollinated.  Wind pollinated flowers have a rather haphazard method of dispersing their pollen; it's random and inefficient and so they need to produce a huge  number of pollen grains for every ovule.  They're insignificant because they don't need to attract a pollinator with showy petals and scents.  But they fill the air with their pollen and it gets up our noses.

Insect- and bird-pollinated flowers have a much more efficient mechanism for dispersing their pollen, one that delivers it reliably to another flower.  Because it's so much more efficient, they don't need to produce so much pollen, and it's not out there in huge amounts causing misery to folks like me.

You might think I'd hate all grasses.  I have to admit I don't find them very interesting. But I do like this genus, Briza:

It sucks to be a botanist who's allergic to flowers.

Tuesday, 8 November 2011

How small can flowers get?




Te Ikaamaru Bay


Myosotis brevis
Myosotis brevis, the flower is about 1 mm across.

Peperomia urvilleana
The oystercatchers were making a racket.
Oystercatchers among cape weed, Arctotheca calendula.

Limosella lineata
Mercury Bay weed, Dichondra repens
Colobanthus muelleri
Eryngium vesiculosum

Sand spurrey, Spergularia rubra

Field madder, Sherardia arvensis

Friday, 4 November 2011

Nettles without stings

Every plant family name is typified by a genus, which means the name of the family is based on the name of a genus.  For instance, the name Brassicaceae, for the mustard family, is based on the name Brassica, which is the so-called type genus of the family.  But it would be a mistake to think the type genus is necessarily typical of the family in any other way. Viola, with its bilaterally symmetrical flowers and capsular fruits, is not a typical member of Violaceae, nor is wind-pollinated Plantago typical of Plantaginaceae.
The same applies to the nettle family, Urticaceae.  Most people have been stung by nettles, and I used to think, wrongly, that this is a family of stinging plants.  Heywood et al. (2007, but see Hadiah et al. 2008 for an update) refer to five tribes in the family and mention stinging hairs for only one, the Urticeae.  Interestingly, all five tribes are represented in New Zealand, suggesting the members of this family may be easily dispersed.
Tribe Urticeae includes the widespread temperate genus Urtica, which has five native and four naturalized or casual species in New Zealand.  These nettles all have stinging hairs, but U. australis on the subantarctic islands has very few of them. 
Urtica australis on Enderby Island, Auckland Islands.
Nettles often grow in nitrate-rich environments and they can accumulate rich nutrient reserves in their leaves.  This makes them a target for herbivores and the stings are an effective protection from some grazers.  Nevertheless nettle soup is a traditional dish in Europe.  Also nettles are readily eaten by caterpillars and thus they provide environmental support for butterflies.  I wonder if U. australis has few stinging hairs because it has few natural predators in its subantarctic home.
Urtica australis, flowers and a few hairs
New Zealand has one of the most spectacular nettles, Urtica ferox (the name means fierce) or ongaonga.  Ongaonga stings can be fatal, especially to horses and dogs, but humans have also been affected.  One botanist colleague has had a lucky escape, only just managing to stumble out of the bush in time.  Friends called an ambulance when they found him numb, partly paralysed, and disoriented.
Ongaonga, Urtica ferox.
The stiff stinging hairs are like little (not so little in ongaonga) hypodermic needles that inject the toxins under the skin.  The brittle tip of the hair breaks off on contact, and as the hair is pushed into the sac of toxins at its base the toxins are forced up its hollow shaft.  These toxins include formic acid, serotonin, and histamine according to Wikipedia, while some species contain oxalic acid or tartaric acid.  Connor and Fountain (2009) mention a toxin called triffidin that may also be involved.
With such active chemicals, it's no surprise that Urtica is widely used in herbal medicine and homeopathy.  Homeopaths believe that a substance that causes a symptom in a healthy person can be used to treat that same symptom in a sick patient. They also believe the more dilute a solution is, the more powerful it is as a treatment, even when so dilute that none of the original substance remains. They combine those two principles and believe highly diluted nettle extract is a remedy for skin rashes.
Nettles in the tropical genus Dendrocnide grow as small trees with very dangerous stings, and another genus Laportea is also notorious.
Parietaria judaica
The rest of the family is not so scary.  Parietaria judaica (pellitory, Tribe Parietarieae) is a common weed around Wellington city and many other parts of the country.  There is a native species, P. debilis.  Pellitory doesn’t have stinging hairs, but it is implicated in asthma and skin irritations.
Elatostema rugosum
Elatostema rugosum (parataniwha, Tribe Elatostemeae) is a large herb from the north of New Zealand, where it grows on stream sides and wet cliffs.  There’s also a good patch of it in the Wellington Botanic Gardens, just downstream from the duckpond.  No stinging hairs here either, so it’s an attractive plant for the garden.
Pouzolzia australis (Tribe Boehmerieae) is a small tree found on the Kermadec Islands as well as Norfolk and Lord Howe Islands.
Finally, Australina pusilla (Tribe Forsskaoleae) is a little creeping herb that’s said to be common in coastal and lowland forests.  I think I must often have overlooked it, so now I intend to keep an eye out for it.
So all these New Zealand Urticaceae are stingless nettles except for Urtica.  They shouldn't be considered to have evolved from ancestral plants that had stings, since stings seem to have evolved only in Tribe Urticeae.  Stinglessness doesn’t mean they’re entirely benign though.  The flowers in this family are small and wind pollinated, and the copious pollen production associated with wind pollination makes them a minor cause of hayfever.
Connor HE, Fountain J 2009.  Plants that poison—a New Zealand guide. Manaaki Whenua Press.
Hadiah JT, Conn BJ, Quinn CJ 2008. Infra-familial phylogeny of Urticaceae, using chloroplast sequence data. Australian Systematic Botany 21: 375–385.
Heywood VH, Brummitt RK, Culham A, Seberg O 2007.  Flowering plant families of the world. Firefly.