Taxonomy of Setaria viridis
Kingdom: Plantae (plants)
Family: Poaceae (the grasses, also sometimes called Gramineae)
The genus Setaria is also part of informal groups of plants. These groups don’t follow traditional Linnaean taxonomy, but are important in understanding plant diversity. Setaria are:
- Angiosperms (flowering plants)
- Monocots (flowering plants whose seeds have one cotyledon, have parallel leaf veins and flower parts in multiples of three)
A Setaria Species Near You
Now that you have been introduced to the green foxtail millet, Setaria virids, does it look familiar to you? Do you think you have seen it growing near you? There is a good chance that you have! There is also a good chance you have encountered a few of its close relatives too. There are four closely related species in the Setaria genus that are commonly found in North America. Although we find them all over North America, they originated in Eurasia, and were probably introduced as humans traveled to and settled in North America. These species are invasive weeds, and when they grow in agricultural areas can lead to smaller crop yields.
The bristly foxtail millet (S. verticillata) and the bur bristlegrass (S. adhaerens) can be identified by the Velcro-like feeling of the panicle. Pointed barbs on the panicles of these species cause the seeds to stick to animals’ fur or human clothing. When these sticky seeds attach, they are dispersed to another location, helping the plant population spread. In the United States bristly foxtail millet is widespread but uncommon, while bur bristlegrass is found only in the southernmost parts of the country.
The green foxtail millet (S. viridis) and the nodding millet, or giant foxtail (S. faberi) are more commonly found, but can be difficult to tell apart. The nodding millet has a panicle that often bends over, or appears to “nod.” If the plant has not yet matured to form panicles, it can be difficult to tell apart from S. viridis. The nodding millet is often taller than the green foxtail millet, but the wide variation in size of S. viridis can make this distinction difficult to make. Although the ones in your classroom may be small, some types of S. viridis can grow over 1.5 meters tall! The simplest way to tell them apart is to look closely at the upper surface of the leaf blades. If the leaf blade is smooth, then it is S. viridis. If there are tiny hairs on the leaf blade, it is most likely the nodding millet. The nodding millet is also more sensitive to drought, so you will more often find S. viridis in dry places (like cracks in the sidewalk).
Scientists at the Donald Danforth Plant Science Center have carefully collected species from the genus Setaria to closely study the genetics, morphology (the form and structure) and the environments these plants live in. Would you like to practice collecting these plants too? Watch the video below of Daniel Layton from the DDPSC to learn how. (NOTE: Only collect plants from areas in which you have permission! Don’t go on others’ private property or in parks or nature reserves.)
Video: How to Voucher a Plant Specimen
So where did these closely related species come from? Genetic analysis can give us clues, especially when we look at the number of copies of each chromosome (a tightly packed strand of DNA) a plant has. Humans are diploid, meaning that we have two copies of each of our chromosomes. Some plants, however, can have more than two copies of each chromosome. S. viridis is diploid, and appears to be the ancestor of some other Setaria species:
- The nodding millet (S. faberi) is a tetraploid, meaning it has four copies of each chromosome. When S. viridis, with two copies of its chromosomes mated with another unknown species, which also had two copies of each chromosome, a new species with four copies of each chromosome was formed – the nodding millet.
- The bristly foxtail millet species was formed in a similar manner. However, its ancestral parents were S. viridis and the bur bristlegrass (S. adhaerens).