A Neotropical Savanna

If I were taking a course in botany, I’d be lucky if I were averaging a “C.” I am still too eager to get to an ID – I’d like to know a name, a family, something about the plant, and move on.

This attitude gets me into trouble. I zero in on a feature or two and think that is sufficient information to tell me what the plant is. Almost inevitably, I’m wrong.

Case in point. When I returned from my annual visit to the U.S., a small tree was in bloom near my favorite nance tree.

I took pictures, looked at the plant, even sketched a bit of it. Then I went to Keller’s key for identifying plants based on vegetative characteristics. I followed the features – I thought – down to a family I had never heard of, but which sounded very interesting. Feeling sure of myself, I sent off some images and my idea of an ID to a botanist at the Field Museum in Chicago who has helped me before. Almost by return email he kindly informed me that I was entirely wrong – that my plant belonged to the Asteraceae family (the Aster, or Sunflower, family), and that it was probably what used to be called a Eupatorium, the genus of Boneset and, at least formerly, Joe-Pye Weed.

I was stunned and humbled. How could I have made such a mistake?

It was not the fault of Keller’s key. It was my own hurry, and my misreading of a couple of significant characters. But even if I had used the key correctly, and had been lead to the Asteraceae family, I might have at that point thought I was doing something wrong.

When I think of the Aster family, I think of sunflowers and daisies, and now, from here in Panama, the so-called Mexican sunflower, Tithonia, which was also in bloom when I returned from the U.S. “Aster” means “star,” and my mental image is of a sunflower – a kind of star of the prairie. The Aster family used to be called the Composite family for reasons that will become clear shortly, and a statement from Lady Bird Johnson has stuck in my mind all these years – a statement about the difficulty of identifying those “darn yellow composites.”

The pattern of most flowers
I went back to my very first botany book, Botany in a Day, by Thomas Elpel, to zero in on what it is that makes a plant a member of the Asteraceae family. As it turns out, flowers of the Aster family are more complex than flowers from almost any other family. The flowers of most families have, if you look down upon them:

• a ring of sepals
• a ring of petals
• a ring of stamens (male reproductive organs)
• a pistil or pistils (female reproductive organs) in the middle

A cross-section of most flowers would look something like this illustration from the Biology Department of the University of Cincinnati Clermont College:

The pattern of Asteraceae flowers
By contrast, flowers of the Aster family have:

• bracts (modified leaves) where you would expect sepals – often in multiple layers
• ray flowers (usually) where you would expect petals
• disk flowers in the middle – here at last are the flowers most like those found in other families, though tiny, with microscopic sepals, petals, stamens, and pistils

Hence, the flowers are really “composites” of different kinds of very small flowers – hence the earlier name, Compositae, for the family. You can get an idea of the complexity of the flowers of this family from the following diagram. It’s from a great web page on Dahlias from Stanford University.

Botany gets even more complicated, though, when you learn that some members of the Aster family have both ray and disk flowers, some have disk flowers only, and some have ray flowers only. So how do you know when you have an Aster family plant in hand? According to Elpel, it’s pretty straightforward: look for multiple layers of bracts beneath the flowers. Also, look inside the flower head for the presence of many smaller flowers.

So…here we go with my flower:

First, look at the “puffball” flowers on the plant:

Then, look closely at a puffball:

You can start to tell that the puffballs are made up of pretty small flowers. Let’s zero in and look for them and for those bracts:

There they are: 1) the presence of many smaller flowers, and 2) multiple layers of bracts beneath the flowers. (Those bracts look a little like miniature artichokes, don’t they? Yes! Artichokes belong to the Asteraceae family!)

Let’s try for a closer look at some of the flowers:

It’s clear from the Asteraceae drawing taken from the Dahlia page that there’s even more to the flower than this. But at least with the naked eye we can see 1) united petals – there are 5 of them to each flower, 2) united anthers – I only know this because of the location within the flowers; the male anthers surround the female pistils, and 3) two long, club-ended pistils, united from the tip of the petals down toward the bottom of the flower.

It used to be called a Eupatorium
Even with all this looking, I haven’t seen enough, or know enough botany, to identify the plant. The botanist at the Field Museum said it was probably “what used to be called a Eupatorium.” A “typical” Eupatorium was beautifully illustrated by John Curtis who was really painting bugs (British Entomology (1824-1835))- the link is at the DELTA description of the Compositae family, under Illustrations:

Before moving on, I’d like to look into that name. Dave’s Botanary says that Eupatorium is

Named for Mithridates VI Eupator, King of Pontus [a region on the south coast of the Black Sea, now in Turkey (wikipedia)] about 115 BC who is said to have discovered an antidote to a commonly used poison in one of the species.

A poison in one of the species. Hmm. Once upon a time, the genus Eupatorium was thought to have as many as 800 species. Now that number is down to somewhere between 36 and 60. (wikipedia) So which species Eupator found the antidote for is still unknown to me.

What’s happening in taxonomy
How the number of species in the genus got reduced by more than tenfold, though, is the story of what’s happening in plant taxonomy, or, more properly, plant systematics, these days. For many, many years, plants were identified by what they looked like – the shape and arrangement of leaves, for instance, the arrangement of the flower parts, and so forth – and by their chemistry – the color of the sap, for instance, or the aroma. The chemistry of plants may have been of primary importance to the very early botanists, because plants were looked to as sources of medical treatments. Early botanists tended to group together plants with similar medicinal properties. Many visible plant features corresponded with these groupings, so it made sense to rely on such external features in the absence of knowledge about medicinal properties.

In recent years, botanists have been trying to place plants in groups based on how closely related, in an evolutionary sense, they are. They are using genetic data, ecosystem data, distribution data (biogeography) as well as traditional chemical and morphological data. It is no longer just a matter of trying to find some order in the plant world and giving names to this order, which was more or less the thrust of taxonomy. It is a matter of looking at the whole system – hence, plant systematics.

This approach will be useful in the long run, and will really help us understand the plant world better, but at present it causes a great deal of confusion among those of us who are not professional botanists but who would like to know a little something about plant relationships. Whole families are being re-defined, the Aster family, formerly known as Compositeae, is one example. And the Eupatorium genus within that family is another example.

As redefined, the Eupatorium genus no longer is found in Central America. Indeed, the entire subtribe to which it belongs – the Eupatoriinae – are “virtually absent from Mexico through Central America.” (Schmidt & Schilling) This subtribe seems to be truly genetically related and includes Boneset, Joe-pye weeds and other genera found in North America and Asia.

The plants from Central America that used to be called Eupatorium have been moved to other genera, including Ageratina, Fleischmannia, Koanophyllon, and Mikania. (wikipedia) I mention these 4 genera of the 13 listed in wikipedia because they have been found either in Costa Rica or in Panama.

And there I must stay, hanging in suspense, not knowing the name of the plant until a kindly Panamanian botanist can take a look at my pressed sample.

Unidentified, but not unappreciated
In the meantime, I’d like to spend a moment with the plant in its entirety. The plant is growing in a cluster of other plants near my nance tree. I can imagine that the cluster there in that place arose from seeds in the droppings of a bird, a bird that sat in the branch of the nance tree.

Here are the flower head (inflorescence), the bracts, and the tiny flowers that make it recognizable as a member of an Aster family:

The leaves, stem, and trunk:

And, with a wink to John Curtis’s British Entomology, a bug among the bracts.