How to identify a plant

When you encounter a plant that you do not know, it is natural to want to know its name.  In my previous post, I described some ecological disasters that resulted from scientists misidentifying plants used in experimental studies or in habitat restoration.  I also provided a reference where numerous incidences of accidental poisoning have occurred through consumption of misidentified food or medicinal plants.

Can you tell the difference between the two specimens below? Two people in Italy were recently hospitalized for confusing them.  The one on the left is fennel, the one on the right is poisonous Hemlock, two species out of hundreds in the carrot family, Apiaceae. Though there are clear differences, including flower color and leaf shape, you would have to know them from experience or have them identified by an expert before using them.

Photo by Alvesgaspar - Own work, CC
BY-SA 3.0, httpscommons.wikimedia.
orgwindex.phpcurid=15855012

Photo in public domain,
https://commons.
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?curid=2740278

its name.  In some cases, it may be critical to ID it correctly: if you're using a plant in a scientific study, if it's something you may eat or take as a medicine, if your child has eaten something that might be poisonous, or if you're selling plants of some supposed horticultural or medicinal value.  The list goes on and on.  In my

So what do you do?  If it's important, you at some point will have to consult an expert.  You can use available tools to identify it yourself, or at least narrow down the possible identities.  If you have a deep interest in plants, learning identification skills can be time well spent.  It will sharpen your eye for detail and deepen your understanding of plant diversity and adaptation.  If, however, you are a mother in a panic about what your child just put into his mouth, skip this step!

In either case, you need to gather as much baseline information as possible:

1. Is it wild plant, or a cultivated one?  There are different tools for these fundamental categories.

        If it is a wild plant, and you know where it came from, you've already
greatly limited the number of possible plants. There are typically field guides, keys, pictorial guides, and specimen depositories (herbaria) for specific regions of the world, that you can avail yourselves of.

        If it is a cultivated plant, where it was growing is also important.  Plants cultivated in south Florida are quite different from what can be grown in Maine, and there are often regional guides for cultivated plants.

2. What plant parts do you have to work with? Though a good forensic botanist may be able to ID seeds, pollen grains, or wood fragments, generally a good sample of the foliage as well as the flowers and/or fruit is necessary for identification.  Photographs are helpful, but the actual physical material is important for examining small details.

If the above information and materials are fairly complete, you are in a good position to seek out an appropriate expert, or plunge on yourself.

The primary job of plant taxonomists is to inventory the plant
life of the Earth.  Here, taxonomists Heinar Streimann
and Peter Stevens work with local villagers to pack up
plant materials that will be dried and deposited in
 around the world as reference specimens.  Photo taken on an
expedition to Aseki, Papua New Guinea in 1972. When not
in the field, taxonomists continue their research in plant
diversity, teach students, and identify specimens sent in by
others. 

A.  Finding an expert.  Plant identification experts are called taxonomists or systematists, and they reside primarily at herbaria and botanical gardens. If there is such a facility locally, that will be your first contact. In most states, there is at least one major herbarium, usually at the primary state university or at your state's designated agricultural college.  In big states, like California, Florida, Texas, and New York, there are several major herbaria.  A local county agricultural extension agent may know many of the plants cultivated locally, and can also direct you to the nearest herbarium.  Outside of the US, each country has a similar network of regional and national herbaria.

Once you locate a herbarium and confirm that they are willing to look at your material you can take your specimens to them, or send them by mail if it's too far to drive there.  Once your materials are in the hand of a professional plant taxonomist, you are connected to the network.  If your local taxonomist can't fully ID your plant, he or she can at least narrow it down to a plant family, genus or other grouping and send it off to a specialist.  Some places will charge a fee, particularly for commercial purposes, others will do it for free.  If it's a common local plant, they may be able to give you the ID instantly.

But experts frequently turn to other experts for critical identification of uncommon plant materials.  Each typically has his or her own particular genus or family that they have spent years studying, which often have specialized terminology or details that require years of training and practice to recognize.  In the grass family, for example, we have to distinguish between paleas, lemmas, glumes, and awns, and in mosses we have calyptras, peristomes, opercula, etc. In the genus Sphagnum, the distinguishing characters not only have funny names, but can only be seen in special preparations under the light microscope.

Now, if you're that panicked mother, you've already wasted valuable time reading the above paragraphs.  You should already be at the hospital!  The baseline information, and a sample of the plant material will still be very important in identifying the poison and administering the appropriate antidote.  The information here will, however, help prepare you for future incidences and to avoid poisonous materials in the future.

B. Plunging on yourself.  How do you start?

You don't have to have a PhD in plant taxonomy to begin the identification process, narrow the plant ID to a handful of possibilities, or possibly even come up with the correct scientific name for the plant. It's a challenge, but can be a very rewarding learning process.  The tools available run the gamut from pictorial guides that anyone can use, to more technical keys that require some learning and practice.  There are books and a growing list of useful websites to help with identifying plant materials of a particular type or geographic origin.

Pictorial wildflower guides, like this one for
South Africa,can be very useful, but you must
pay close attention to detail - there are many
look-alikes due to similar adaptations for
pollination. 

You can begin with non-technical field guides that contain descriptions and color photographs, usually arranged by flower color, or sometimes by habitat.  These are available for many states, national parks, or other specific regions.  These are not usually comprehensive, but contain the most common species. If you come up with a possible match, you can do a web search for images to confirm.  But beware - you can get many erroneous hits, typically of other plants that might be on the same web page as the plant you're looking for.

You can move from that beginning to more formal floras or handbooks, which contain all known species for a specific area with technical descriptions and identification keys.   An identification key takes you through a series of either-or questions that progressively narrow the field of possibilities.  A key might begin

More advanced references,
like Wunderlin and Hansen's
Guide to the plants of Florida,
require the use of technical
keys and specialized
terminology.

with "flowers red" vs "flowers yellow."  Depending on your choice, you're directed to a later subsection of the key that deals only with plants with red flowers or the one that deals only with yellow flowers.  So, if you were faced with a possible 1000 plants at the beginning of the exercise, after the first step, you could potentially be down to 500 possibilities (more or less, depending on how many red and yellow flowered plants are actually in the area).  You could get really lucky and find that there is only one red-flowered species in the area, and you have it.  Simple, right?

Well, not always.  Keys in general are notoriously difficult, even sometimes for trained taxonomists.  First, you have to learn a lot of specialized terminology. You have to know the names of all the parts of a flower, and the parts of each flower part, and there are typically special names for unique forms of flower or fruit parts found in particular families or genera.

Professional taxonomists typically reduce the time they spend with keys with various shortcuts.  The most important of these is to learn to recognize the various plant families.   Keys to the families are particularly difficult as the technical characteristics that distinguish modern plant families tend to be rather obscure.

Someday, we might be able to just "google" a plant by entering in an image for "facial recognition."   An experienced taxonomist can often recognize instantly plants that he has seen before, sometimes even just by the hue and pattern of colors in a field.  I's the sames as when you see someone you know.  You don't have to measure the length of your spouse's earlobes or the precise color of their eyes to identify them.  A taxonomist likewise, doesn't have to laboriously count ovary locules or measure the length of anthers in order to identify a plant he or she has seen before.  So a similar sort of facial recognition of plants may be possible with computers in the future.  Another tool that may eventually allow for instant identification would be some kind of DNA scanner, a Star-Trekish tricorder, if you like.

For now we still need professional taxonomists, and in fact a large number of them will be needed to program the above technology!)  This is all the more reason that it should be alarming that taxonomists are dwindling in numbers, as I pointed out in my previous post, and as eloquently pleaded by the famous Indian taxonomist R. R. Rao.