Sorghum bicolor
Poaceae subfam. panicoideae
grain sorghum, great millet, Milo, shattercane, sorghum
50-500+ cm tall, 1-5 cm thick, sometimes branching above the base;
nodes glabrous or appressed pubescent;
internodes glabrous.
annual, usually solid, sometimes somewhat woody, sometimes decumbent, often branched above the base.
distichous;
sheaths usually open;
auricles usually absent;
abaxial ligules usually absent, occasionally present as a line of hairs;
adaxial ligules membranous, sometimes also ciliate, or of hairs, sometimes absent;
blades sometimes pseudopetiolate;
mesophyll radiate or non-radiate;
adaxial palisade layer absent;
fusoid cells usually absent;
arm cells usually absent;
kranz anatomy absent or present;
midribs usually simple, rarely complex;
adaxial bulliform cells present;
stomata with triangular or dome-shaped subsidiary cells;
bicellular microhairs usually present, with a long, narrow distal cell;
papillae absent or present.
5-60 cm long, 3-30 cm wide, open or contracted, primary branches compound, terminating in rames with 2-7 spikelet pairs;
disarticulation usually not occurring or tardy.
ebracteate (Paniceae) or bracteate (most Andropogoneae) panicles, racemes, spikes, or complex arrangements of rames (in the Andropogoneae), usually bisexual, sometimes unisexual;
disarticulation usually below the glumes, frequently in the secondary and higher order axes of the inflorescences.
bisexual or unisexual, frequently paired or in triplets, the members of each unit usually with pedicels of different lengths or 1 spikelet sessile.
usually 2, equal or unequal, shorter or longer than the adjacent florets, sometimes exceeding the distal florets;
florets 2(-4), usually dorsally compressed, sometimes terete or laterally compressed;
lower florets sterile or staminate, frequently reduced to a lemma;
upper florets usually bisexual;
lemmas hyaline to coriaceous, lacking uncinate hairs, often terminally awned;
awns single;
paleas of bisexual florets well-developed, reduced, or absent;
lodicules usually 2, sometimes absent, cuneate, free, fleshy, usually glabrous;
anthers 1-3;
ovaries usually glabrous;
haustorial synergids absent;
style branches 2, free and close or fused at the base.
often exposed at maturity.
hila usually punctate;
endosperm hard, without lipid;
starch grains simple;
embryos large in relation to the caryopses, usually waisted;
epiblasts usually absent;
scutellar cleft present;
mesocotyl internode elongated;
embryonic leaf margins usually overlapping, rarely just meeting, x = 5, (7), 9, 10, (12), (14).
1-2.6 mm.
1-4 mm;
blades 5-100 cm long, 5-100 mm wide, sometimes glabrous.
spikelets bisexual, 3-9 mm, lanceolate to ovate;
calluses blunt;
glumes coriaceous to membranous, glabrous, densely hirsute, or pubescent, keels usually winged;
upper lemmas unawned or with a geniculate, twisted, 5-30 mm awn;
anthers 2-2.8 mm.
spikelets 3-6 mm, usually shorter than the sessile spikelets, staminate or sterile.
= 20, 40.
Sorghum bicolor
Poaceae subfam. panicoideae
Sorghum bicolor was domesticated in Africa 3000 years ago, reached northwestern India before 2500 B.C., and became an important crop in China after the Mongolian conquest. It was introduced to the Western Hemisphere in the early sixteenth century, and is now an important crop in the United States and Mexico. Numerous cultivated strains exist, some of which have been formally named. They are all interfertile with each other and with other wild species of Sorghum.
The treatment presented here is based on de Wet (1978) and is somewhat artificial. Sorghum bicolor subsp. arundinaceum is the wild progenitor of the cultivated strains, all of which are treated as S. bicolor subsp. bicolor. These strains tend to lose their distinguishing characteristics if left to themselves. They will also hybridize with subsp. arundinaceum, and these hybrids can backcross to either parent, resulting in plants that may strongly resemble one parent while having some characteristics of the other. All such hybrids and backcrosses are treated here as S. bicolor subsp. xdrummondii.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
The subfamily Panicoideae is most abundant in tropical and subtropical regions, particularly mesic portions of such regions, but several species grow in temperate regions of the world. Within the Flora region, the Panicoideae are represented by 59 genera and 364 species. They are most abundant in the eastern United States (Barkworth and Capels 2000). Photosynthesis may be either C3 or C4. All three pathways are found in the subfamily, but the PCK and NAD-ME variants appear to have evolved only once, while the NADP-ME pathways seems to have evolved several different times (Giussani et al. 2001).
The Panicoideae were first recognized as a distinct unit by Brown (1814), earlier than any of the other subfamilial taxa of the Poaceae. Its early recognition is undoubtedly attributable to its distinctive spikelets. Recognition of the tribe Gynerieae is recent (Sanchez-Ken and Clark 2001) and its placement in the Panicoideae, rather than the Centothecoideae, should be regarded as tentative.
Spikelets with two florets are found in many other subfamilies, but rarely do they follow the pattern of the lower floret being sterile or staminate and the upper floret bisexual. Development of unisexual florets within the Panicoideae appears to be consistent across the subfamily (LeRoux and Kellogg 1999), but differs from that in the Ehrhartoideae (Zaitcheck et al. 2000).
The Paniceae and Andropogoneae have their conventional interpretation in this Flora, so far as the North American taxa are concerned. Molecular studies, however, while strongly supporting the monophyly of the Andropogoneae, show the Paniceae to be paraphyletic, with two distinct clades. In one of these clades, most taxa have a chromosome base number of x = 9, but some have x = 10, and the taxa are pan-tropical in origin. The taxa in the other clade, with one exception, have a chromosome base number of x = 10 and are American in origin. This latter clade is sister to the Andropogoneae, which also have a chromosome base number of x = 10 (Gomez-Martinez and Culham 2000; Giussanni et al. 2001; Barber et al. 2002).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Inflorescences branches remaining intact at maturity; caryopses exposed at maturity; sessile spikelets 3-9 mm long, elliptic to oblong | subsp. bicolor |
1. Inflorescences branches rames, disarticulating at maturity, sometimes tardily; caryopses not exposed at maturity; sessile spikelets 5-8 mm long, lanceolate to elliptic. | → 2 |
2. Rames readily disarticulating | subsp. arundinaceum |
2. Rames disarticulating tardily | subsp. ×drummondii |
1. Blades of leaves on the lower 1/2 of the culms disarticulating from the sheaths; plants 2-15 m tall, unisexual, without axillary inflorescences; blades with midribs 5-15 mm wide | Gynerieae |
1. Blades of most or all cauline leaves remaining attached to the sheaths; plants 0.05-6 m tall, usually bisexual, sometimes with unisexual inflorescences, often with axillary inflorescences; blades with midribs 0.2-5 mm wide. | → 2 |
2. Glumes usually conspicuously unequal; lower glumes usually greatly exceeded by the upper florets; upper glumes from subequal to longer than the distal florets; lemmas of the upper florets usually coriaceous to indurate; disarticulation usually beneath the glumes, not in the axes of the inflorescence branches | Paniceae |
2. Glumes usually subequal, usually exceeding and concealing the florets; lemmas of the upper florets hyaline to membranous; disarticulation frequently in the axes of the inflorescence branches | Andropogoneae |
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