Identification

Many people think of botanists simply as people who can rattle off the Latin names of plants.  Charles Dickens seemed to be reflecting this with his character Wackford Squeers in Nicholas Nickelby: 

• "... bottiney, noun substantive, a knowledge of plants.  When he has learned that bottiney means a knowledge of plants, he goes and knows 'em.  That's our system Nickelby, what do you think of it?"

Biological identification is the process of assigning a biological sample to membership of a group.  Usually it means giving it a name.  If we're talking about a species level identification, we're making a judgement that the sample belongs to a particular species rather than any other.  Say you see a small four-legged furry animal and you say it's a cat.  What is the process behind that decision?

Rufus, a cat.

First, what is a cat?  In common English language uses, cat could mean one of a number of things.  It could be the biological species Felis catus, the domestic cat.  It could be any one of the other species in the cat family, such as a lion or a tiger.  Or it could be one of a number of other animals that are not strictly cats, such as the meerkat or the civet cat.  In other languages there are other names, le chat in French, el gato in Spanish.  In biology though, the scientific name for the domestic cat, Felis catus, is international and more importantly it's strictly defined by a type specimen, usually a museum specimen that is permanently attached to the scientific name, for reference and stability.  If you try to tell me a meerkat is Felis catus, we can compare it with the type specimen and see if you're right.

But even then, it's not entirely objective, because we're using the process of identification.  Technically we're looking for identity between the type specimen of Felis catus and our meerkat.  And strictly speaking, individuals in the same species are rarely identical (even identical twins have different fingerprints).  So whether two individuals are the same species or not is often a matter of opinion.  Thus we use the term identity in the sense of belonging.

Because of the type system in biology, we can say the type specimen is Felis catus, but every other cat is only identified as Felis catus.  It's a matter of opinion that they belong to the same species, but in the case of cats, and even more of our own species, that opinion is based on a considerable amount of experience and knowledge.  When it comes to organisms that are less like us, it becomes harder to decide if two individuals belong to the same species or not.  Unicellular algae can appear to be identical, yet be unable to interbreed and have quite different DNA sequences.

Branches from this plant near Franz Josef Glacier were collected, pressed, and mounted as a herbarium specimen to be the type specimen of Veronica colostylis (although originally it was called Parahebe linifolia subsp. brevistylis).  Advance of the glacier has wiped out that locality, but plants of the species are still common in the valley, and the type specimen is preserved in the Allan Herbarium at Landcare Research, with duplicates in several other herbaria.

There are many different ways that biologists decide which individuals belong to the same species, sometimes called species concepts.  The best functional definition is the Biological Species Concept (BSC), because this is a genetic definition: a species is a breeding population, or group of interbreeding populations.  Genetically, a species has a gene pool, made up of all the different alleles (gene variants) that are capable of being combined with each other because they're found in individuals that can interbreed.  An allele that's only found in a dog will never combine in nature with one that's only found in a cat, because these two are different species and can't be interbred.

DNA sequencing gel

While the BSC is a useful conceptual and functional definition of a species, it's not used very often to identify individual specimens.  It's simply too bothersome and time-consuming to try all the interbreeding experiments that might be necessary.  Instead, we use a proxy.  Often it's their morphology (the Morphological Species Concept or MSC): if two individuals look the same, or at least very similar, they're reckoned to belong to the same species.  And if we want to give our sample a name, we need to compare it either directly or indirectly (through a description or photograph) with a type specimen.  Recently there's been a lot of interest in using short DNA sequences as identification markers for species, so-called DNA barcodes.

 Morphology works as a proxy for the BSC because we know empirically that members of the same biological species usually look very similar.  But two problems arise with the Morphological Species Concept.  First, species can be very varied.  Sometimes males and females look very different, some barnacles for example.  Other times, juveniles and adults can look so different they're mistakenly classified as different species, as in many kinds of eels.  Sometimes there are polymorphisms like striking colour variants within a breeding population.  In plants and some animals, different forms may be produced in different environments, like the inchworms that grow to be camouflaged on whatever host plant or plant part they're feeding on, or at different times of the year.

Secondly, there are cryptic species, those that look the same but are separate breeding populations.  Sometimes they have physical, timing, or genetic barriers to successful mating, but if we rely on the MSC we'll not discover these.

Veronica odora plants in the North Island and northern South Island (also in the Auckland Islands) have two sets of chromosomes (diploid), but in the central and southern South Island they have four sets (tetraploid).  Probably these two chromosome races can't interbreed and should perhaps be treated as cryptic species, even though I've found no way they can be distinguished based on their morphology.

 So a biological identification is a matter of opinion, but that certainly doesn't mean anyone's opinion is as good as anyone else's.  Taxonomists who study the classification of groups and who understand the nature of their variation and breeding relationships will be more reliable than Wackford Squeers who just "knows 'em".  That's because their identifications are based on a sound understanding of the evidence.  And we can future-proof and error-proof our identifications by keeping a record of what the plant or animal was, preferably as a museum specimen.  That way, if we got it wrong or if the name changes in the future, someone can always check back and bring the identification up to date.  A name in a notebook, publication, or database that hasn't been safeguarded in this way is practically valueless.

Specimens are also important for resolving disagreements about identification.  I remember being called once by a botanist who firmly told me not only had I got the distribution of Sonchus arvensis wrong in a Flora treatment (Webb et al. 1988), but I hadn't described it accurately either.  Fortunately my initial horror and embarrassment gave way pretty quickly to a potential alternative hypothesis, so I asked for a specimen to be sent by mail.  You can guess where this is going, I hope: to my relief, the specimen was Picris echioides.