What is Setaria?
The simplest answer is that Setaria spp. are a genus of flowering plants commonly referred to as foxtails, bristlegrasses or millets. But if you’d like more detail I encourage you to read on…
What kind of a plants are Setaria spp.?
Setaria is a genus of monocot plants within the grass family (Poaceae). The Poaceae is a large, diverse clade of plants (5th largest) that can be divided into subfamilies and further subdivided into tribes.The genus Setaria falls into the tribe Paniceae, which is a specific group of evolutionarily related plants within the Panicoideae subfamily. As a subfamily, the Panicoideae is a large one, comprised of approximately 3,300 species of grasses characterized by panacoid growth morphology and an abundance of species that perform C4 photosynthesis [1,2].
The Panacoideae encompasses many economically important plants (Figure 1) including grain crops (maize, sorghum, pearl millet and foxtail millet), biofuel feedstock materials (sugarcane, switchgrass, Miscanthus) and weedy agricultural pests (guinea grass, many species of foxtail/bristlegrass).
What is the evolutionary history of Setaria?
Species within the genus Setaria are believed to have initially evolved in Africa before a diploid annual species similar to Setaria viridis (green foxtail) spread throughout Eurasia . Further evolution and adaptation enabled the colonization of semi-tropical and eventually temperate climates . Concurrent with this era of specialization of Setaria viridis (green foxtail) in Eurasia, Setaria pumila (yellow foxtail) evolved and expanded its distribution throughout China .
The habitation of Setaria spp. in the New World (the Americas) is a consequence of two distinct eras of arrival . It is estimated that Setaria parviflora (knotroot bristlegrass) arrived from Asia along with humans between 10-20,000 years ago making it the first Setaria spp. to colonize the New World and only Setaria species truly native to the Americas [4,5]. All other Setaria spp. are believed to have arrived much later, likely during the post-Columbian era (last 500 years) as a consequence of international traffic and human dispersion .
What are some major species of Setaria?
The genus Setaria is comprised of at least 125 different species . Let’s take a moment and look at six species of Setaria commonly found here in North America:
Foxtail millet (Setaria italica)
Foxtail millet is a domesticated grain crop. It is referred to commonly by many names including foxtail millet, Italian millet, German millet, Chinese millet, Hungarian millet, kangni, korra, tenai, navane, thina, chamai, kavalai, kambankora, xiǎomǐ (小米), awa (粟), and jo (조) [6,7]. It is the second-most widely planted species of millet globally and the most economically important millet within arid regions of northern China . As a cereal crop, grains are typically prepared like rice or porridge but can also be ground into flour, fermented or eaten raw. In Europe and North America foxtail millet is a relatively minor crop primarily used for the production of hay, silage and as a component of animal feed . More recently in Colorado, there has been some interest in using foxtail millet grains as a gluten free alternative to wheat and barely .
Foxtail millet is one of the world’s oldest domesticated crops. Current estimates suggest that domestication may have occurred between 5,900-8,700 years ago within China and other locations throughout Eurasia [4,9,10]. The earliest evidence of cultivation comes from the Neolithic era in the form of phytolith evidence at the Cishan site in the North China Plain . The European cultivation of foxtail millet as a crop occurred later, likely around 3,600 years ago .
Foxtail millet varieties can be subdivided by plant and panicle morphological characteristics into three different landraces: moharia, maxima and indica [4,11]. More recently, a molecular analysis of Eurasian landraces suggests the existence of five different geographically distinct groups [4,12]. Morphologically, foxtail millet is an annual grass, ranging 1-2 M in size at maturity with a dense hairy panicoid seed head of roughly 5-30 cm . A much more detailed description can be seen here. The distribution of Setaria italica within North America is illustrated here.
Green foxtail (Setaria viridis)
Also known as green bristlegrass, bottle grass, pigeon grass, and wild millet, green foxtail is an agricultural weed.
Its ability to survive in and adapt to harsh environments has enabled Setaria viridis to globally expand its geographical range beyond its native Eurasia to become one of the most widespread plant species on Earth . Green foxtail can be found growing in many types of urban, cultivated and disturbed environments including: along roadsides, railways, within lawns and vacant lots or on the margins of agricultural fields.
Based on cytological and molecular evidence it is presumed that Setaria viridis is an ancient progenitor of cultivated foxtail millet (Setaria italica) [4,13,14]. Smaller than Setaria italica, it can be distinguished from other Setaria spp. by the lack of trichomes on the surface of vegetative leaves and seed characteristics. A much more detailed description can be seen here. The distribution of green foxtail across North America can be viewed at the following link.
Yellow foxtail (Setaria pumila)
Yellow foxtail is another commonly found agricultural weed also referred to as yellow bristlegrass, pigeon grass, and cattail grass. Yellow foxtail evolved in China during the rapid expansion of Setaria spp. throughout Eurasia .
Although primarily considered a weed, evidence suggests that seeds gathered from wild species were later cultivated in India as a kharif crop called Korali [4,15].
Morphologically, it is very similar in size and growth habit to Setaria viridis but the presence of long trichomes on the adaxial leaf base and boxy panicle allow for accurate identification. A much more comprehensive set of criteria can be viewed here. One can view the distribution of Yellow foxtail in North America by clicking on this link.
Giant foxtail (Setaria faberi)
Also known as Chinese foxtail, Chinese millet, giant bristlegrass and nodding foxtail, Setaria faberi is another weedy Setaria species. Current literature suggests that giant foxtail evolved in southern China through an extremely rare allo(tetra)polyploidization event giving rise a fertile Setaria viridis X italica hybridization product [4,5] although recent unpublished data from Dr. Elizabeth Kellogg’s lab may indicate alternative evolutionary origins [Daniel Layton personal communication].
Giant foxtail was first introduced to North American in the 1920s near New York City, before spreading to Philadelphia, Missouri and across much of North America .
Giant foxtail can be distinguished by its large size, panicle that droops down as it reaches maturity and abundant trichomes on the adaxial surface of vegetative leaves. A more detailed description can be found here. One can view locations in North America where giant foxtail has been observed here.
Barbed bristlegrass (Setaria verticillata)
Another weedy species barbed foxtail is also referred to as hooked bristlegrass or bur bristlegrass. A european native , this foxtail is also widely distributed across North America. One major distinguishing feature of Setaria verticillata is the presence of backward pointing barbs on the panicle which can hook onto clothing or animal fur aiding in seed dispersal. As such, Setaria verticillata seed heads feel sticky to the touch. Click here for a more thorough set of criteria describing the characteristics of barbed bristlegrass and here to view its distribution within North America.
Knotroot foxtail (Setaria parviflora)
Knotroot foxtail is unique from all the other foxtails described above for two reasons. It is the only Setaria spp. considered native to North America and it is the only perennial species. Evidence suggests that a Setaria relative, likely knotroot foxtail, was the oldest cultivated grain crop in the Americas with cultivation occurring as far back as 9,000 years before present . As a perennial, it can produce up to three seed crops per growing season . Typically found in wet, marshy areas it is able to colonize salt prairies as well as salt marshes so long as the water level remains relatively low . Other names for this species include marsh bristlegrass, yellow bristlegrass and bristly foxtail. A more comprehensive set of morphological descriptors can be viewed here. To view the distribution of this species within North America visit the following link.
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