The Notanist's Guide to Understanding Floras and Dichotomous Keys

To be continually revised

People find it odd that I don't call myself a botanist. I still don't call myself one.

I think such labels are limiting, discouraging, and even misleading. Most people don't consider themselves botanists. Heck, if I were to survey every person in the world and ask, "are you a botanist?" I would guess that less than 1% of people would say yes. Everyone else, not a botanist—or notanist, if you want to save a few syllables.

However, there are plenty of wonderful plant people who are not academically trained or working as a professional botanist. Being a botanist is not a requirement for being interested in plants, or a requirement for learning to key them out. To me, "notanist" signifies not an inability to enjoy and appreciate plants, but the potential inside every person to become do things which we would deem exclusive to "botanists." Birders are not ornithologists, but they know their birds and they can make important contributions (see bat falcon).

The point is, just because you're not a botanist doesn't mean you can't use a flora book. The purpose of this document is to "Bob Ross" botany - you too, can identify plants using dichotomous keys!

Flora Books: The One Book to Rule them All

Taxonomic treatments (like this one) are like Rings of Power in Lord of the Rings, granting the user the ability to identify any plant in so-and-so genus, although often you can only exercise that power within a limited domain. But if taxonomic treatments are Rings of Power, then the flora book is the equivalent of of the One Ring.

A flora book is an incredibly powerful botanical weapon. It is the product of hundreds of collectors, taxonomists and systematists, countless hours in the field and lab, and an unspeakable amount of taxonomic literature. All this is packaged into one large and often dense (both physically and dictionally) book which you can hold in your hands.

Well... you can't probably hold every single volume of Flora of North America in your hand, but you get the point. Whoever holds this book holds the culmination of hundreds of years of botanical work, and the blood, sweat and tears of many a botanist. Whoever holds this book holds immense botanical power in their hands.

Want an example? Here is the Manual of the Vascular Plants of Texas.

Whoever holds this book and has the stubborn persistence to use it has the theoretical power to identify nearly every plant in the state of Texas. Pretend you have that book in your car. Think about that. Can you imagine having that amount of power... a book which you can put in your car and take around Texas, taxonomically obliterating basically every plant within sight?

Note that I said theoretically. Generally, you can't open up a flora book and immediately gain botanical superpowers. But with a little bit of knowledge and experience, and a good amount of stubborn persistence, you too can harness the power of the One Book.

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. There's a reason why art museums have plaques beside their paintings.

Describing and referring to a plant with words: again, the words are difficult to interpret by themselves. Ideally one would have the actual plant live 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, though, you can get close.

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 does. 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. Also, many flora books will have glossaries within them as well; Flora of North America has a categorical glossary which can be found online in database form here.

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.

If I look at the plant right after you read the first statement, then I get biased towards "finding" that trait on the plant. It's more likely I'll say it's true... without ever checking if the other one is better. On the other hand, if I look at both, and then look at the plant to decide which one fits better, you don't feel as much of a preference for either one. Put it this way: forget the plant for a few seconds and just read the leads without thinking whether the plant fits one or the other.

This can be tricky when there's multiple characters in the couplet—say it uses leaf shape, pedicel length, flower color—I find that by the time I finish reading the first lead, beginning to end, and start reading about the leaf shape on the second lead, I've forgot the leaf shape in the first lead!

  • Leaves widest below the middle, ovate to lanceolate; pedicels 0.75-1 times the length of the subtending leaf; corolla pale yellow to white.
  • Leaves widest at or above the middle, obovate; pedicels 1-5 times the length of the subtending leaf; corolla red or orange.

What seems to work better for me is to go trait by trait. Read leaf shape for one; then the other; then look at the plant, and decide which fits better. Do that for the next trait, and the next. Keep track of which lead you chose for the first traits. You might not have a clear answer for all the traits listed—that's okay, go read Tip 7.

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. Flora of North America for example has a lot of excellent line drawings for many plant genera.

Example: These are photos of a Gratiola species I found:

In key couplet 6 in the Flora of North America key to Gratiola, the couplet uses the number of sepal-bractioles to distinguish the species. I looked at the flower heads (right image) and wasn't sure what were the bracteoles and what were the sepals! Reading the description, I noted that this genus had flowers with 5 sepals, meaning that 2 of those 7 "sepals" were bracteoles... likely the two longer ones on the lateral sides.

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.

The best reference visuals, in my opinion, are botanical illustrations within a flora book or taxonomic source. Even if your flora you use has no images, you may be able to find illustrations from a different flora. Looking at plants of the same genus might help you determine how a character varies. For example you could determine what the male and female flowers look like to tell if a plant is monoecious or dioecious, or figure out what the heck ochrea are in the key to Polygonum. Some illustrations are really useful, but other times they can be pretty unhelpful too. But I trust them the most.

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.

My notes on Texas Datura species, derived from the Manual of the Vascular Plants of Texas.

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 9 months ago

Excellent advice. I love using well written floras to verify plant identifications but frequently reach dead ends. Very often on circling back in the keys I find a statement was misread or misinterpreted. Patience is needed as wells as making reference to the correct part of the plants structure (stigma vs style for instance). Also watch out for couplets where there are strings of character states separated by "ors", only one of the phrases may apply to your sample. Well written keys will put the word "or" in caps (OR) for emphasis and to keep you on your toes.

I have a specific question regarding FNA series keys:

Puzzled by the key structure used in some versions of FNA. For instance in the beta version of the generic key for Malvoideae there are a number of couplets where there are statements without an apparent alternative character state (for instance see couplets 3, 4, 6 and 7). Perhaps I am overlooking something but I cannot understand how to progress through keys with this layout. Please help me understand how to use this type of key. See:

Posted by geoplant 17 days ago

@geoplant I was not aware of that structure in the FNA keys. It also appears that some couplets are inaccessible in (couplets 5, 6, 7, and 8) i.e. it would be impossible to reach those couplets from the . My interpretation would be that there are some mistakes on the online FNA version of those keys, but I will check the print version and ask for outside opinion to make sure.

Posted by arnanthescout 16 days ago

Hello Arnathescout,

Thanks for looking at that FNA key. Searched the FNA website for description of how keys are constructed but found no detailed explanation. Also think there was at least one similar couplet in the key to Abutilon. Odd there could be so many errors.

We are away and do have hard copies for many FNA volumes at home, but not sure if I have the volume that includes Malvaceae.

Are you aware of an email contact for the FNA series? I wrote one member of the editorial committee at random but do not see an option for general inquires.

Again, thanks for looking into this.

Posted by geoplant 16 days ago

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