The Notanist's Guide to Understanding Floras and Dichotomous Keys

To be continually revised
Notanist: A portmandeau of "not" and "botanist." It means exactly what it sounds like it means.

To describe a plant with words is like describing a work of art with words.

Describing and referring to a artwork with words: by themselves, the words are meaningless gibberish. Only by looking at the artwork does one start to understand what the words mean. Yet words can also describe things that are not obvious at first sight, deeper things that one would not have noticed before, and garner a greater appreciation for the piece at hand.

Describing and referring to a plant with words: again, the words are difficult to interpret by themselves. Ideally one would have the actual plant in front of you, but that is not always practical, so images serve as a substitute. Although, in a similar way that you cannot truly portray a vase or sculpture in images, you can never really portray a plant in images. It's always best to experience it for yourself. With proper documentation, you can get close, though.

Ok. So imagine a gallery of Monet's impressionist water lily paintings. See them? Alright. Imagine describing each and every one of those paintings in words. And then a step further: imagine telling someone how to tell those paintings apart using just words. And then putting that all in a book.

That, in essence, is what a flora book is. What you are trying to do is to look at a painting, look back through the book, and determine through all that writing which painting you are looking at. Indeed, it's a difficult task. However, with the points that I outline below, I hope that it becomes even just a little more manageable for you.

Tip 1: Don't overwhelm yourself. Start small.

I would not recommend starting out with Flora of North America. There is often such a large amount of species that you will quickly be overwhelmed. Even US state-level might be too much, depending on how big or ecologically diverse aforementioned US state is.

Work first from a smaller local flora book; I use Flora of North Central Texas. Once you feel comfortable, work up to something larger. Exceptions would be any groups or genera with relatively few species. It's easier to start working from several local species than a dozen or so nationwide.

Tip 2: Have a botanical glossary on you. With illustrations/images. And maybe a few other sources to check vocabulary.

There is no way a layperson would be able to read a flora book. Botanical terms practically consist of a completely different language!

As confusing as it may seem, there is a purpose to this language, which is to make keys, descriptions, and other botanical works considerably more concise. Think of the terms as shortcuts: "pedicel" instead of "stalk holding flower to stem," rachis instead of "that stem-like part which runs through the center of the compound leaf." Concise words versus botanical charades. To the student of botany, though, they present a great obstacle in deciphering keys and descriptions.

Solution: have a good botanical glossary on you, preferably one with illustrations if you're just starting out. A picture is a thousand words, so they say. Botanical terminology is significantly easier if you have an image of the part which said term corresponds to. I use Plant Identification Terminology: An Illustrated Glossary by James G. Harris and Melinda Woolf Harris. In addition to the traditional alphabetical glossary, terms are also sorted by category (leaf shape, stem indumentum, inflorescence types) which I find rather convenient. In lieu of an actual book, the GoBotany website has an online pictorial glossary one can use.

It's useful to have multiple sources to refer to. Sometimes a term will have multiple definitions. Pubescent can refer to having short, soft hairs, or having any kind of hairs. As with finding out the meaning of any sort-of word, look at the surrounding words and sentence for context in order to determine the definition.

You may need multiple sources to get an understanding of the definition of a term. This could include a normal dictionary and Google. Images are always helpful if you can find good ones.

Tip 3: Working from a larger flora? Simplify the key; rule out unlikely candidates

This applies to field guides as well. Start by eliminating species that are not known to occur in your area. I use BONAP (Biota of North America Program) maps, which organizes county-level maps by genus, so it's easy to determine which species in a genus occur in your county. The USDA plants database also has maps with its species profiles as well (you can zoom in on the maps to show county). With the USDA site you could also go to genus and check subordinate taxa maps, although I prefer BONAP for that. Also, if your flora book has a page with distribution maps for species, prioritize those as they will probably be more accurate than the other two mentioned.

Once you know what species occur in your area, you can focus on only those species in the key, which makes the keying process less overwhelming. For example, where I live only C. involucrata, C. leoicarpa, and C. pedata occur, so in the FNA key I can focus on those three rather than all 9 of them.

Tip 4: Read both statements in a couplet before choosing a lead

Sometimes the first option seems right and you feel you don't have to read the other one. It is however important to read both before making a decision, in the same way that it is recommended you look at all the answers on a multiple choice question before making a choice. Weigh them equally, then decide.

Tip 5: Don't understand? Take your time. Work couplet by couplet, word by word.

Sometimes you will grasp a couplet immediately. Sometimes... you won't. If you encounter the latter case, reread the couplet, with your botanical glossary. There's no need to rush through it... relax, take your time. Know what the words mean. Though understanding the meaning of the words is not always enough, which leads me to my next point...

Tip 6: Know which character corresponds to what on the plant

In other words, know the plant's morphology. Where is character X on your plant?

A short explanation of characters and character states:

  • Character: anything that can have more than one form/variation. Examples: Petal color, inflorescence type, leaf shape
  • Character states: things used to describe a character state. Examples: Red/white/light pink, panicle/cyme/raceme, ovate/deltoid/lanceolate

Leaves lanceolate
Character is leaf shape, character state is lanceolate

Sometimes, the petals are a lie; they're actually sepals! In all seriousness, though, it's difficult to understand whether the bracts on a plant are auriculate or lanceolate if you don't know which part of the plant is the bract.

A flora book with illustrations may be of great help here, especially if you're just beginning. Look at images of other plants in the genus. Reading the genus description might help too. It will get easier with experience.

Tip 7: A key often has multiple ways to distinguish taxa in a couplet. Use the ones that work best for you.

If a key is being annoying then it'll just reference one character (like seeds...), and if you don't have that on the plant, you're kind of stuck. Nicer keys will have multiple character-character state pairs, aka multiple ways to distinguish a pair of taxa. Use whichever way works best for you. Ideally, one would be able to use all characters listed in a couplet. However, if one part of a couplet confuses you, or is practically impossible to tell with images or even with the plant at hand (because of phenology), then look at the other ones. Focus on what you can understand.

Tip 8: Use the species descriptions to your advantage

A key cannot list everything about a plant and tell how it's different from each of the other species—that would take too long! The dichotomous key system reduces the information, making things more efficient. However, this extra information is still both useful and important. Thus, a good treatment will have a description for each taxon, which you can use to supplement the key.

At a couplet with a terminal taxon and a number lead: if you are uncertain, read through the description of the taxon and see if anything clearly disagrees with your specimen.

Narrowed down to 2-3 taxa: at this point, go ahead and read through the description of each taxon, noting differences, and evaluate your plant from there. The extra information often comes in handy. Think of the 2 descriptions as an extended key, where you can create your own couplet and comparative characteristics to look at.

Once you have reached a single answer, check and see if the species description matches up with your plant.

Tip 9: Referencing images: iNaturalist observations, herbarium specimens and other images can be accurate, but not always. Check them with literature, take them with a grain of salt.

Misidentifications happen, whether on iNat or in the herbarium, and that is something to be aware of. Take them with a grain of salt: check those "examples" with the literature. If working from iNaturalist observations, find an observation from a botanically-experienced user, someone who does understand floras and dichotomous keys. Those are significantly more likely to be accurate.

Herbarium specimens may or may not be more accurate with identifications. Also, they are often pressed/arranged such that you can see everything you need for identification e.g. top/bottom of leaves, calyx or phyllary details, pedicel or peduncle length relative to something else. Specimen sheets are often available to view online at various websites. Take advantage of those too.

Tip 8: Synthesize: rewrite the key in your own words and images

This is all about making that knowledge in the flora book your own. Write out the differences between commonly confused taxa, explain the meaning of the botanical terms. Draw out pictures on the margins showing what "hirsute" or "puberulent" mean. I can not emphasize this enough. Transform the key into something that you can better understand.

Tip 9: It comes with time. Practice. Be stubborn. Eventually, you will get it.

It took me approximately 2 years to "get" floras and dichotomous keys. Even then, I still struggle to use them. It won't happen overnight. As with all things it takes practice.

Practice using keys, even if you already know the species off the top of your head, or if it seems obvious or easy. Sometimes keys seem hard because you only ever resort to them for the difficult taxa. Practice with an easier group of plants that you are familiar with. I find that with difficult keys you won't know for sure if you are going the right way. But if you're doing a group of plants you can already identify without a key, you will know for sure when you messed up somewhere.

Be meticulous and stubborn. I will do anything in my power to get a plant to species, if possible.

When overly frustrated with something, shelve it and return to it later. After some breathing time and some more key-wrangling experience, you just might get it.

Posted on November 24, 2022 08:50 PM by arnanthescout arnanthescout


I love that advice, "Be stubborn." Thanks for writing this!

Posted by atlasmira 8 days ago (Flag)

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