Basic Plant Identification: Part 1

Henbit and purple nettle
To the left, Purple Dead Nettle (Lamium purpureum) and to the right, Henbit (Lamium amlexicaule)

A few weeks ago when I was talking about my love of sidewalk weeds and identifying plants, some of you had written to me saying you wanted to learn more.  In my last post on this topic we talked about some characteristics of plants but I was unable to show examples due to the time of year and the slim pickings of available plant life.

So let’s start with the photograph at the top of this page. These plants seem to look almost the same at a quick glance and many times people either mistake the one for the other or do not realize at all they are entirely different plants.  They are common lawn “weeds” so you have probably seem them before. They are in the same family (Lamiaceae) and the same genus (Lamium)  but are different species.   As I mentioned before, it is often difficult to be able to key a plant down to the species. If you (as an amateur like myself) get to the genus that is pretty good but if you can actually just look at a plant and identify the family, that is excellent.

Example of “opposite” arrangement of leaves

For these plants, lets start with the leaves.  The example above is called opposite leaves because the leaves are directly across from each other along the stem.  The example below show leaves that are called whorled because the leaves surround the stem (think of it as lots of opposite leaves together rather than just two).

Whorlled leaves
Example of “whorled” arrangement of leaves

Another characteristic of leaves that is important are the edges of the leaves. The examples we have here (see below for a close up) fall into the category of toothed edges because the edges of the leaves have little teeth (as opposed to being smooth).  In out last post  on this topic, we looked at wild ginger leaves that had a smooth edge and that was called an entire leave.

toothed or lobed edges
Examples of “toothed” edges of leaves

Here is another characteristic to look for: the shape of the stem. Notice in the close up below that the stem is square (I just am showing one but both these plants have a square stem).

square stem
Square stem

So now you know what a Toothed leave is.  You also know two very important characteristics (opposite or whorled leaves and square stems) of a very common plant family: Lamiaceae.  Why should you care? Well, the family Lamiaceae is more commonly known as the mint family.  Next time you tend to your basil, oregano, thyme, or rosemary plants take a look at the position of the leaves and feel the stem.  Now there are other characteristics that make these plants part of the mint family. It is important to know that because there are also other plants with opposite leaves and square stems that are not part of the mint family and perhaps we can look at those characteristics another time.  But for now, pat yourself on the back for getting to know the members or your herb garden on a different level.

Identifying Plants by Keying

If you have read my other posts on collecting weeds and wild plants, then the term keying may sound familiar so here is my long promised attempt at explaining that process. You may wonder, why not just snap a picture and run it through an app on your phone?  Part of the fun of keying is like solving a puzzle.  Also, if someone is really interested in botany, just learning the name of something really does not teach anything about the characteristics of a plant. Since keying can become quite involved, what I will do is give a general explanation for the mildly curious. Perhaps some point in the future, I will go into greater detail about plant characteristics; and with it being January, the examples I can provide at the moment are pretty slim pickins!

A sampling of plant key guides

First, lets talk about the types of key guides that are available.  There is the professional key (which I do not own) and those for amateurs, like the ones pictured above.  Different guides use different systems for identification but the one thing they all have in common is the need to identify certain characteristics of the plant in question. It is of the most importance that whatever guide you choose, that the time is taken to read the introduction to the guide and directions on how to use it.

So keeping with general information, listed below are some of the most basic characteristics you will need to know to begin using whatever key guide you choose.

  • If it is an herbaceous or woody plant – example: a woody plant means a shrub, there are also vines (which can be woody or non woody but generally are just classified as vines in a key), and herbaceous plants which are other flowering plants like our friends the weeds and other wildflowers.  These keys do not include trees or grasses (both of which also flower) because those types of plants are a whole different ball of wax.
  • Characteristics of flower/fruit/seed – this includes the number of parts, if is regular or irregular. Parts of a flower include the petals, sepals, female & male parts (pistil & stamen), and if the flower is regular or irregular (in a very basic sense this has to do with the shape of the flower).
  • Characteristics of leaves – this includes the position of the leaves, what the edges look like, the overall shape, and if it is simple or compound.  The wild ginger leaf on the right is considered entire because the edges are smooth.


After the basic characteristics of the plant have been determined, depending on the key, you will either be guided through the book with a group of symbols and compare your specimen with additional plant characteristics until you reach something that looks like your plant. Alternately is a system where a number is assigned to each characteristic and the group of numbers helps to guide you through the key until you come to something that resemble your plant. Each of these systems are great fun and you may choose to use just one type of key or several.  I use several but my favorite is the one that uses a number system (I will pause here to let those of you who know me laugh hysterically because you know my aversion to anything to do with numbers).

Useful tools for keying include a ruler, tweezers, a jewelers loop, and pencil/notepad

The system with the numbers is called the Newcomb system and I like it because it goes into great detail as to exactly what the plant looks like. However, the Newcomb system was written for the Northeastern US/Canada.  This does not mean it is not useful elsewhere because you can still track a plant to at least the family or genus. This was the first key I ever used and in the beginning there were many of days that I wanted to toss it across the room. But with increased understanding of what I was looking at and practice, I now find it to be quite easy. If you are only mildly interested in this process, I would recommend one of the guides that uses symbols such as the ones in the Finders series (these are the ones in the top right of my key guide photo).

This is where I will stop my description on keying because to go further would require better examples than I can collect at this time. Also, some readers may just have wanted their curiosity satisfied and I hope this has served that purpose. At some point in the future, when I can get better samples to photograph, perhaps I can go into some more detail on plant characteristics for those who are curious. But for now, That’s all folks!