There are two ways to measure chemical diversity and complexity.
We can simply look at the numbers of classes of chemicals produced by a large group like the monocots, whether there be just one example of that chemical class or many examples. This is a measure of chemical richness of a family or plant group.
The second way is to look at what degree each chemical group is represented, the variety of its related products, and relate these to the numbers of species engaged in this process. This is a measure of chemical diversity. A plant group can, like the monocots, be chemically rich. But due to limited representation of these various types of chemicals, the diversity of these plant groups as their own unique entities with measurable diversity features, can be fairly limited.
For example, a family with just a few members, each producing one each of these chemicals per plant, may have a richness that seems full and ecologically capable–all 3 are represented–however, they lack chemical diversity; each member with this chemistry is limited to just one chemical. A diverse group of these three plants would be a situation in which each of the three plants bear two or more of the same three classes. The result is this population has a better opportunity for continued survival. Whereas only one might might survive the first evolutionary test with the first group, two or more will survive with the second group.
The following is the distribution of chemicals and/or related ethnobotanical uses for the Monocotyledons, by subclass. The number of genera per item measured is provided for the bar charts.
It should not be a surprise that the most chemically complex subclass is Liliidae and the least chemically complex subclass the Alismatidae. Notice the high medicine productivity of Liliidae, Commelinidae, Zingiberidae, Aridae, and Palmidae, in descending order. Since there are relatively few genera in the paleotypic Aridae, this is a little misleading. But otherwise, if we combined the bar chart evidence with the pie chart evidence we get a much better idea on the distribution of the major plants uses at a subclass level. When each subclass is reviewed, the details of this distribution of chemical-ethnobotany features can be better understood, and even predictable at times.