This may be a stupid question, but I’ve been looking at keys for various genera in different areas, and find that at times they seem to vary quite a bit. At times I can see a point because the inclusion of different species may change the way it’s easiest to handle things, but I was looking at two earlier which included the same four species but tackled them differently. Is this likely to be because:
- There are regional differences within species, so what works to distinguish species in one area doesn’t in another
- The keys are written by different people who’ve chosen to focus on different aspects
Or is it something else I’m not seeing or haven’t thought of?
I guess I ask (a) out of interest, but also because (b) if it’s the first, it may be important to use the key from the correct area.
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in my experience, this is often the reason
some keys are also based on dried herbarium material vs others based on live specimens in the field, in which case you will also get different features focused on
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often the differences in keys make it easier to confirm an id
It is generally good practice to use the key for the region it was made for, but even then there will be multiple keys.
With plants: different authors choose different methods, and some like to create a key not reliant on flowers or able to be keyed when deciduous
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*cries in European Daphnia* :,)
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Sometimes the case - subtle variability across a range, different subspecies and so on. Different authors may give different weight to characters (and thus order their keys differently) because of that.
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This is often because a different location has different species. Let me give a basic example.
In Texas, there are three species: two have red flowers and one has white flowers. each has very small but distinct seeds.
In Arizona, only one of the red species is found, as well as the white one, and there is a third species with blue flowers. The seeds of the white and blue flowers are indistinguishable, but white prefers clay-rich soil and blue prefers sandy soil.
The Texas key and Arizona key may both choose to start with flower color, which is often obvious. Unless, of course, the flowering of these plants is so brief it is often missed.
The Texan key would be justified immediately going to seeds as this easily yields the three relevant species. If the Arizona key did this, it would still need another step.
Or the Arizona key might use soil type, which is not relevant for the Texas key.
Even if both places had the same four species, a species can have a different habit in different biomes. Or perhaps they crossbreed in one area and not another.
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Keys often have errors in, either just a mistake or perhaps the author hadn’t seen enough specimens of the rarer species to appreciate how variable they are. So you would hope the more recent keys have corrected these problems and are the most reliable.
The more keys you have, the better. If one keys uses, for instance, a character in the antennae and your specimen has lost its antennae, you’ll need an alternative character. And some people just don’t like particular couplets and devise alternatives.
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Thanks for all those answers - some interesting points raised that I hadn’t thought about, as well as some confirmation of things I’d already assumed.
PS Keys that only work if you catch the species on the right three days (give or take) in the year are frustrating!
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If you are lucky - the authors of your field guide are active on iNat - and you can ask them directly!
@ johnmanning and @ botaneek for me
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Keys like that are indeed frustrating. I suspect that’s one of the reasons @charlie got so frustrated by what he saw as too many splits (I hope I’m not simplifying his argument too much).
But if that’s the best or only way to distinguish species in an expert’s opinion, then we ordinary naturalists have to accept it and leave observations at genus. Sometimes, there’s a gestalt about an organism that iNat’s CV and experienced observers can pick up, but often that’s hard to convey in photographs, and I worry about variability among individuals.
It’s a difficult issue. I’m fine with leaving observations at genus; many people aren’t.
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In addition to what others have already written, there are different approaches to how dichotomous keys can be arranged (and therefore the characters chosen). See https://en.wikipedia.org/wiki/Single-access_key#Diagnostic_(‘artificial’)_versus_synoptic_(‘natural’)_keys
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