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Setaria (BRISTLEGRASS or FOXTAIL GRASS)
Dr. Charles Allen [email protected]
The identification of grasses requires the learning and understanding of several botanical terms that are unique to the Graminoids (grasses, sedges, and rushes plus some other look a-likes). The saying that if you have seen one grass leaf, you have seen them all is fairly accurate. There is not much variation in grasses leaves, all are alternate so no opposite, all are simple so no compound, no palmate veins, no lobes, etc. There is some variation in pubescence, especially the margins, some in the shape of the base, and very little in the tips. Some id can be made by looking at the ligule which is found on the upper side of the leaf at the juncture of the blade and sheath. The ligule varies in type (some are membranous and some are tufts of hairs), size, and presence or absence. So, the identification of grasses relies heavily on the flowers, yes grasses do flower but all have naked flowers, no sepals and no petals.
All grasses produce their flowers in spikelets. A spikelet is an axis along which florets are produced with one or two scales called glumes at the base. Each floret consists of an upper scale called the lemma and a lower scale called the palea. The grass flower is produced between these two scales and consists of a pistil and stamens, the flower is naked, no sepals and petals. The pistil after fertilization will become the fruit which is termed a caryopsis, defined as a one seeded dry fruit where the seed is completely fused to the ovary wall. It is difficult to separate the ovary wall from the seed and is the reason that corn (a grass) is soaked in lye water so as to be able to get the ovary wall off and make hominy. Hominy is the seed only of corn. Spikelets vary in number of florets, number of glumes, shape, etc. There are two major groups of grasses, those whose spikelets are laterally flattened (flattened from the side so the spikelet has distinct edges) and those that are dorsally flattened (flattened from the back so the spikelets are rounded).
Spikelets are arranged in an inflorescence on the grass plant and that can be useful in identification. There are four types of inflorescences in grasses; spike, rame, open panicle, and contracted panicle (also called a spike-like panicle. In a spike, the spikelets are attached directly to the main stem and do not have a stalk or pedicel and this can be seen in wheat and barley. A rame has branches with the spikelets attached by a short pedicel to the branch and can be seen in bahia grass and crab grass. The open panicle is the largest inflorescence and the pedicel is branched often several times. Switch grass is a good example of an open panicle. If the spikelets are on branched pedicels but the whole inflorescence is contracted and looks like spike, this is the contracted panicle. Close examination is required to distinguish a true spike from a contracted panicle.
The genus Setaria often called foxtail grass or bristlegrass is best recognized by its contracted panicle, dorsally compressed spikelets, and the one to many bristles that surround the spikelet. One species (palmifolia) does have an open panicle. Each spikelet consists of two florets with the lemma and palea of one floret hard or indurate. There are ten species (one with two varieties) of Setaria reported for Louisiana.
The two most common and wide spread species of Setaria in Louisiana are Setaria pumila (yellow foxtail) and Setaria parviflora (knotroot foxtail). Setaria parviflora is reported from 60 parishes (all except Ascension, Assumption, Iberville, and West Feliciana). Setaria pumila includes two varieties (variety pumila reported from 59 parishes, all except Cameron, St Mary, Vernon, Washington, and West Carroll and var pallidefusca reported from 24 parishes (Ascension, Assumption, Caddo, Calcasieu, Cameron, Concordia, East Baton Rouge, Jefferson, Lafayette, Lafourche, Lincoln, Orleans, Ouachita, Plaquemines, St. Bernard, St. Charles, St. James, St. John the Baptist, St. Mary, St. Tammany, Tangipahoa, Terrebonne, Washington, and West Feliciana). In both of these species and the variety, the 4-12 bristles below each spikelet are antrorsely scabrous, the fertile (hard) lemma and palea are rugose, and the sheath margins are glabrous. Setaria parviflora is a perennial and the spikelets are elliptic and mostly shorter than 3 mm. Setaria pumila is an annual and the spikelets are broadly elliptic to ovate and mostly longer than 3 mm. The variety pallidefusca has reddish bristles and dark green leaves while variety pumila has tawny or yellow bristles and light to yellow green leaves. Setaria pumila was known for many years as Setaria glauca and Setaria parviflora sailed under the name Setaria geniculata.
The oddest species is Setaria megaphylla (synonym – palmifolia) (Palmgrass) with an open panicle and palm like large leaves. Bristles are only present below some of the spikelets and not all as is the case of the other species of Setaria. This is a cultivated species and only two records (Orleans and St Mary parishes) are reported for the state.
The two Setaria species with retrorsely scabrous bristles are Setaria adhaerans (burr foxtail) and Setaria verticillata (hooked foxtail). Setaria adhaerans has the upper sheath margins glabrous, blades pubescent and spikelets mostly shorter than 2 mm. It is reported from an old herbarium record from Plaquemines Parish only. Setaria verticillata has the upper sheath margins pubescent, blades glabrous, and spikelets mostly longer than 2 mm. It is reported only from Morehouse and Plaquemines parishes.
Setaria magna (giant foxtail) and Setaria italica (foxtail millet) both have smooth lemma and paleas and the spikelets fall but the glumes remain on the plant. Setaria magna is the largest (plant and inflorescence) of the native species and has spikelets that are 2 mm or shorter. It is often seen in the coastal marshes and is reported from 19 parishes (Allen, Cameron, Catahoula, East Baton Rouge, Iberia, Jefferson, Lafourche, Morehouse, Orleans, Ouachita, Plaquemines, St. Bernard, St. Charles, St. Helena, St. John the Baptist, St. Tammany, Tangipahoa, Terrebonne, and Vermilion). Setaria italica is native to Africa where is used for human food and is reported from three parishes (De Soto, East Baton Rouge, and St. Mary). It has spikelets longer than 2 mm.
The other three species of Setaria all have only 1-3 bristles below the spikelet and the sheath margins are ciliate. In Setaria corrugata (coastal foxtail), the lemma and palea are very rugose and the contracted panicle is erect. Both Setaria faberi (Japanese foxtail) and Setaria viridis (green foxtail) have a slightly rugose lemma and palea and the contracted panicle is usually drooping. Setaria faberi has pubescent blades and spikelets longer than 2.3 mm while Setaria viridis has scabrous only blades and spikelets 2.3 mm or shorter. No records for Setaria corrugata have been verified for Louisiana but it is in Mississippi and Texas. Setaria faberi s reported from 25 parishes: Acadia, Caddo, Calcasieu, Claiborne, De Soto, East Baton Rouge, East Carroll, Iberville, Lafayette, Livingston, Morehouse, Orleans, Ouachita, Rapides, Richland, Sabine, St. Charles, St. Helena, Tangipahoa, Tensas, Washington, West Baton Rouge, West Carroll, West Feliciana, and Winn. Setaria italica is reported from 12 parishes: Acadia, Allen, Caddo, Jefferson, Lafayette, Orleans, Ouachita, Rapides, Tangipahoa, West Baton Rouge, West Feliciana, and Winn.
Setaria megaphylla (palmifolia)
Setaria pumila var. pumila
Setaria pumila var pallide-fusca