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corn, cultivated corn

Habit Plants annual. Plants usually perennial.
Culms

(0.5)1-3(6) m tall, (0.5)1-5 cm thick.

7-600 cm, annual, not woody, often reddish or purple, particularly at the nodes, often branched above the base.

Sheaths

open;

ligules usually scarious to membranous, ciliate or not;

blades mostly well-developed, leaves subtending an inflorescence or an inflorescence unit often with reduced blades.

Blades

mostly 30-90 cm long, 2.5-12 cm wide.

Inflorescences

terminal, frequently on both the culms and their branches, sometimes also axillary, usually of 1-many spikelike branches, these in digitate clusters of 1-13+ on a peduncle or attached, directly or indirectly, to elongate rachises, often partially to almost completely enclosed by the subtending leaf sheath at maturity, in some taxa axillary inflorescences composed of multiple-stalked pedunculate clusters of inflorescence branches subtended by a modified leaf;

disarticulation usually in the branch axes beneath the sessile florets, the dispersal unit being a sessile floret, the internode to the next sessile floret, the pedicel, and the pedicellate spikelet (branches with disarticulating axes are termed rames in the following accounts), sometimes beneath the glumes, the branch axes remaining intact.

Spikelet(s)

pairs or triplets komogamous (spikelets in the unit sexually alike) or beterogamous (spikelets in the unit sexually dissimilar);

spikelets of unequally pedicellate pairs usually homogamous and homomorphic;

spikelets in sessile-pedicellate pairs or triplets usually heterogamous and heteromorphic;

sessile spikelets usually bisexual; pedicellate spikelets usually smaller than the sessile spikelets, often staminate or sterile, sometimes absent.

Glumes

exceeding and usually concealing the florets (excluding the awns), rounded or dorsally compressed, usually tougher than the lemmas;

lower florets in bisexual or pistillate spikelets sterile or staminate, often reduced to a hyaline scale;

upper florets bisexual or pistillate, lemmas often hyaline, sometimes with an awn that exceeds the glumes;

lodicules cuneate;

anthers usually 3.

Caryopses

concealed in fruitcases (wild taxa) or exposed (domesticated taxon);

fruitcases of wild taxa distichous, triangular in side view; domesticated taxon without fruitcases, glumes reduced and shallow or collapsed and embedded in the rachis.

Pedicels

free or fused to the rachis internodes.

Pistillate

inflorescences rames or spikes, usually shortly pedunculate (sometimes sessile), solitary, 4-30(40) cm long, (0.5)1-10 cm thick, with 2 or more rows of paired spikelets, hence the spikelets 4 or more ranked, rarely terminating in an unbranched staminate inflorescence.

Staminate

panicles 10-25+ cm, with 1-60(235) branches, internodes 1.5-8.2 mm;

spikelets 9-14 mm long, 2.5-5 mm wide;

lower glumes rounded dorsally, flexible, translucent, papery, loosely enclosing the upper glumes, the 2 lateral veins subequal to the others, not winged.

Photosynthetic

pathway NADP-ME;

bundle sheaths single.

Pedicellate

spikelets variable, sometimes similar to the sessile spikelets, sometimes differing in sexuality and shape, sometimes missing.

x

= usually 9 or 10, or possibly 5 with 9 and 10 reflecting ancient polyploidy.

2n

= 20.

Zea mays

Poaceae tribe andropogoneae

Distribution
from FNA
AL; AR; AZ; CA; CO; CT; FL; GA; IA; ID; IL; IN; KS; KY; LA; MA; MD; ME; MI; MN; MO; MS; MT; NC; NE; NH; NJ; NM; NV; NY; OH; OR; PA; RI; SC; TN; TX; UT; VA; VT; WA; WI; WV; WY; PR; ON; QC; Virgin Islands
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Discussion

Of the five subspecies of Zea mays, only the domesticated subspecies, Z. mays subsp. mays, is widely grown outside of research programs. Three wild subspecies are treated here, albeit briefly, because of their importance as genetic resources for Z. mays subsp. mays.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

The tribe Andropogoneae includes about 87 genera and 1060 species, of which 31 genera and 102 species have been found in the Flora region; some of these have not become established. The tribe is common in tropical and subtropical regions, particularly in areas with significant summer rains, such as the central plains of North America. Two of the grasses that used to dominate the prairies of central North America, Andropogon gerardii and Schizachyrium scoparium (Big and Little Bluestem, respectively), are member of the Andropogoneae. The reddish-purplish coloration that characterizes the culms and leaves of many Andropogoneae gives a striking aspect to grasslands (and lawns) dominated by its members.

Members of the Andropogoneae differ from those of Paniceae in the reduced lemmas and paleas of their florets and, usually, in their paired, unequally pedicellate spikelets, disarticulating inflorescence branches (rames), and the manner in which these branches are aggregated into inflorescences. Unequally pedicellate spikelet pairs are found in many other tribes, but they are more common, and the pedicels more strikingly unequal in length, in the Andropogoneae. Recent molecular work supports recognition of the tribe with one modification of its traditional limits, the incorporation of Arundinella and Tristachya (Kellogg 2000). There is less agreement on the tribe's internal structure and its relationship to the Paniceae (Clayton and Renvoize 1986; Kellogg 2000; Spangler 2000; Guissani et al. 2001).

Inflorescence Structures Describing inflorescence structures in the Andropogoneae is not simple. There is a basic pattern, but its many modifications have resulted in great structural diversity. The following paragraphs provide an overview of this diversity and explain the words and phrases used in describing it. Diagrammatic representations of many of the structures mentioned are presented on pages 604 and 605.

Spikelets Members of the Andropogoneae, like those of the Paniceae, generally have two florets per spikelet, the lower floret usually being reduced in size and sterile or staminate, and the upper floret bisexual (p. 604). Despite this similarity, spikelets of the two tribes are easy to distinguish. In the Paniceae, the lowest glume is usually much shorter than the floret, and the upper florets usually have lemmas that are thicker and tougher than the glumes and lower lemmas. In the Andropogoneae, the glumes usually exceed and enclose both florets, and are thicker and tougher than the lemmas. The florets of the Andropogoneae contrast strongly with the glumes, having hyaline or thinly membranous lemma bodies and hyaline paleas, or, in many cases, no palea. They are almost always completely concealed by the glumes, except that the upper floret often has an awn that projects beyond the glumes.

In some Andropogoneae, the glumes are merely thickly membranous, but most genera have coriaceous or indurate glumes. The lower glumes are sometimes tougher and larger than the upper glumes, and may even conceal the upper glumes as, for example, in Heteropogon (p. 681). In such genera, the lower glumes may be mistaken for lemmas. In dioecious species, or monoecious species with strongly differentiated staminate and pistillate spikelets, the staminate spikelets usually have softer glumes than the pistillate spikelets.

Spikelet Units The basic element of the inflorescence structure in the Andropogoneae is the spikelet unit. These units usually consist of pairs of spikelets, one sessile and one pedicellate (e.g., Saccharum bengalense, p. 615), but they may consist of a pair of unequally pedicellate spikelets (e.g., Miscanthus sacchariflorus, p. 619) or of three spikelets (e.g., Chysopogon fulvus, p. 635). If there are three spikelets in the unit, one is usually sessile and the other two pedicellate, but a few genera, such as Polytrias, have two sessile spikelets and one pedicellate spikelet.

Unequally pedicellate spikelet pairs or triplets are found in other tribes, but in the Andropogoneae they usually differ in size, shape, and sexuality. Spikelet units with spikelets that differ in their sexuality are described as heterogamous; those with sexually similar spikelets are said to be homogamous. Spikelet units with morphologically dissimilar spikelets are beteromorphic (e.g., Andropogon longiberbis, p. 663); those with morphologically similar spikelets are homomorphic (e.g., Chrysopogon zizanioides, p. 636). In most Andropogoneae, the spikelet units are heterogamous and heteromorphic. The sessile spikelets usually contain a bisexual or pistillate floret, and often exhibit features such as awns and calluses that are related to seed dispersal and establishment (Peart 1984); the pedicellate spikelets are usually staminate, sterile, vestigial, or even absent. In some genera the situation is reversed, the pedicellate spikelets being bisexual or pistillate, and the sessile spikelets staminate or sterile. Sterile and staminate spikelets are sometimes morphologically similar to the pistiallye or bisexual spikelets, but usually lack the features associated with seed dispersal and establishment. A few genera have no staminate or sterile spikelets, merely empty pedicels associated dwith the bisexual sessile spikelets, as in Sorghastrum (p. 632) or even, as in Arthraxon (p. 679), with only a stump where the pedicel and its spikelet would be. Inflorescence Structure Further complexity is introduced to the Andropogoneae inflorescence structure by the manner in which the spikelet units are aggregated and the mode of disarticulation. Three patterns can be identified. The simplest pattern consists of inflorescences similar to those common in other tribes, in which neither the rachis nor the inflorescence branches break up at maturity. Genera with such inflorescences [e.g., Miscanthus (p. 619) and Imperata (p.622)] have unewually pedicellate spikelets, and disarticulation is below the glumes. Such inflorescences are, however, in the minority within the Andropogoneae. A more common situation is for the spikelets to be in sessile-pedicellate pairs and disarticulation to be in the branch axes, immediately below the attachment of the sessile spikelets. The resulting dispersal unit consists of the spikelet pair plus the internode that extends from the sessile spikelet to the next most distal sessile spikelet. These disarticulating inflorescence branches, termed rames in this Flora, form the basic unit of the typical Andropogoneae inflorescence. In other publications, the rames are often called racemes, a word that is restricted in this Flora to an entire inflorescence, not just an inflorescence branch. Rames are usually composed of several spikelet units, but sometimes of only one. The spikelets may be evenly distributed, or the base of the rame axis may be naked. Individual plants may bear few to many rames, and the rames themselves may be aggregated in a wide array of primary and secondary arrangements; they may also be branched.

One or more rames may be borne on a single stalk. If this stalk is attached to a rachis, the unit formed by the stalk and its rame(s) constitutes an inflorescence branch. Such a pattern is seen, for example, in Sorghum halepense (p. 629) and Bothriochloa bladhii (p. 647). A more common sit-uation is for one or more rames to be attached digitately to a common stalk, the peduncle. This peduncle may terminate a culm (as in Dichanthium annulatum [p. 638] or Elionurus [p. 686]) or be axillary to a subtending leaf (as in Andropogon hallii [p. 654] and Hemarthria altissima [p. 686]). Each peduncle and its associated rame(s) constitutes an inflorescence unit.

False panicles represent a further level of complexity. In these, the inflorescence units terminate rays, each of which has a prophyll, a 2-veined structure, in its axil. Several rays may develop within the axil of a single leaf sheath, and rays may themselves give rise to subtending leaves with multiple rays in their axils. The result is a complex, tiered inflorescence in which only the ultimate units are easily described. Such inflorescences are found, for example, in Andropogon glomeratus (p. 663) and Cymbopogon citratus (p. 667). Fortunately, identification of the Andropogoneae does not require analyzing false panicles, merely their ultimate inflorescence units.

In another inflorescence pattern, the rame axes are thick and the pedicels are either closely appressed or even fused to the rame axes. In these genera, the pedicellate spikelets are often highly reduced or absent. Pistillate rames of Tripsacum (p. 697) and wild taxa of Zea (p. 700) represent an extreme example of this pattern. In these genera, the sessile spikelets are completely embedded in the rame axes, the lower glumes being indurate and completely concealing the florets. Less extreme examples are seen in Coelorachis (p. 689) and Hackelochloa (p. 694).

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Key
1. Pistillate inflorescences cylindrical spikes, 2-5(10) cm thick, with 8-24+ rows of spikelets pairs, each inflorescence tightly and permanently enclosed by several leaf sheaths and a large prophyll, not disarticulating at maturity; caryopses 60-1000+, not concealed by the glumes; staminate panicle branches not disarticulating below the sessile spikelets, lacking abscission layers; central axis of the staminate panicles polystichous, much thicker than the lateral branches; obligate domesticate
subsp. mays
1. Pistillate inflorescences cylindrical, distichous rames, less than 1 cm thick, with 2 rows of spikelet pairs, each rame usually enclosed by a single leaf sheath and a prophyll, disarticulating at maturity into fruitcases; caryopses 4-15, each one concealed within a fruitcase; staminate panicles composed of rames that disarticulate below the sessile spikelets and have evident abscission layers; central axis of the staminate panicles similar in width to the rames; in the Flora region, wild taxa are known only from research plantings.
→ 2
2. Staminate spikelets (6.6)7.5-10.5 mm long; fruitcases 6-10 mm long, 4-6 mm wide; staminate panicles with 1-35+ ascending to divergent, rather stiff branches
subsp. mexicana
2. Staminate spikelets 4.6-7.2(7.9) mm long; fruitcases 5-8 mm long, 3-5 mm wide; staminate panicles usually with 10-100(235) divergent to nodding branches.
→ 3
3. Leaves pubescent; staminate panicles with (2)10-100(235) branches
subsp. parviglumis
3. Leaves glabrous or almost so; staminate panicles usually with fewer than 40 branches
subsp. huehuetenangensis
1. Leaves smelling of lemon oil or citronella, the sheaths without glandular depressions on the keel; plants perennial, not reaching reproductive maturity in the Flora region when grown outdoors
Cymbopogon
1. Leaves usually not aromatic or, if aromatic and smelling of citronella, the sheaths with glandular depressions along the keel and plants annual; plants reaching reproductive maturity in the Flora region.
→ 2
2. All spikelets unisexual, the pistillate and staminate spikelets in separate inflorescences or the pistillate spikelets below the staminate spikelets in the same inflorescence.
→ 3
3. Pistillate spikelets completely concealed within a hard, globose, beadlike structure (a modified leaf sheath) from which the staminate rames protrude
Coix
3. Pistillate spikelets exposed or enclosed by 1 or more subtending leaf sheaths and a hyaline prophyll; staminate spikelets either distal on the same branch or in a separate inflorescence on the same plant.
→ 4
4. Staminate and pistillate spikelets in the same inflorescence and on the same branch, the staminate spikelets distal to the pistillate spikelets
Tripsacum
4. Staminate and pistillate inflorescences usually separate; staminate inflorescences terminal on the culms and branches; pistillate inflorescences terminal on axillary peduncles, sometimes aggregated in false panicles
Zea
2. Some spikelets bisexual (usually the sessile or more shortly pedicellate spikelet of each spikelet pair or triplet).
→ 5
5. Spikelets apparently solitary and sessile, the pedicellate spikelets absent; pedicels absent or present.
→ 6
6. Culms decumbent, scrambling; leaf blades ovate to ovate-lanceolate; pedicels absent or shorter than 3 mm
Arthraxon
6. Culms erect; leaf blades lanceolate to linear-lanceolate; pedicels always present, usually longer than 3 mm.
→ 7
7. Inflorescences terminal and axillary, composed of digitate clusters of 1-13 rames on a common peduncle; peduncles subtended by, and often partially included in, a modified leaf
Andropogon
7. Inflorescences terminal, with elongate rachises and brancheswith several to many rames; peduncles and branches not subtended by a modified leaf
Sorghastrum
5. Spikelets in sessile-pedicellate or unequally pedicellate pairs or triplets, the pedicellate spikelets often smaller than the sessile spikelets, sometimes rudimentary.
→ 8
8. Pedicels strongly appressed or fused to the thick rame axes, or the rames with only 1 spikelet unit, this a triplet with 2 unequally pedicellate spikelets; bisexual spikelets usually unawned; inflorescences of rames.
→ 9
9. Lower glumes of the sessile spikelets rugose, pitted, tuberculate, or alveolate or the keels winged or with spinelike projections at the base.
→ 10
10. Keels of the lower glumes with spinelike projections on the base, sometimes winged distally, the surface between the keels smooth; spikelets unawned
Eremochloa
10. Keels of the lower glumes winged throughout or not winged, the surface between the keels rough, rugose, pitted, tuberculate, or alveolate; spikelets unawned or awned.
→ 11
11. Sessile spikelets awned
Ischaemum
11. Sessile spikelets unawned.
→ 12
12. Plants perennial; sessile spikelets ovate, the lower glumes smooth, rugose, or pitted
Coelorachis
12. Plants annual; sessile spikelets hemispherical, the lower glumes alveolate
Hackelochloa
9. Lower glumes of the sessile spikelets smooth or scabrous, not sculptured, the keels without spinelike projections.
→ 13
13. Inflorescences false panicles; individual rames to 1 cm long, with 1 spikelet unit; spikelet units composed of 1 sessile and 2 unequally pedicellate and dissimilar spikelets
Apluda
13. Inflorescences usually solitary rames, sometimes with 2 rames in a digitate cluster; individual rames 2-15 cm long, with more than 1 spikelet unit; spikelet units composed of sessile pedicellate pairs, the pedicellate spikelets often rudimentary or absent.
→ 14
14. Pedicels appressed, but not fused, to the rame axes.
→ 15
15. Pedicellate spikelets 1-3 mm long
Coelorachis
15. Pedicellate spikelets 4-8 mm long
Elionurus
14. Pedicels at least partially fused to the rame axes.
→ 16
16. Plants perennial; sheaths mostly glabrous, sparsely ciliate basally
Hemarthria
16. Plants annual; sheaths with stiff, papillose-based hairs 1-3 mm long
Rottboellia
8. Pedicels free; rame or branch internodes slender, sometimes thickened distally; bisexual spikelets usually awned; inflorescences of rames with the spikelets in sessile-pedicellate pairs or of non-disarticulating branches with the spikelets in unequally pedicellate pairs.
→ 17
17. All spikelet units homogamous, frequently also homomorphic.
→ 18
18. Terminal inflorescences a single rame or a digitate or subdigitate cluster of rames.
→ 19
19. Terminal inflorescences a digitate or subdigitate cluster of (1)2-6 rames; rames 3-7 cm long
Microstegium
19. Terminal inflorescences solitary rames; rames 2-3 cm long
Polytrias
18. Terminal inflorescences with elongated rachises.
→ 20
20. Spikelets in unequally pedicellate pairs; disarticulation below the glumes, the branches remaining intact at maturity.
→ 21
21. Spikelets usually awned; inflorescence branches usually 7-35 cm long
Miscanthus
21. Spikelets unawned; inflorescence branches 1-7 cm long
Imperata
20. Spikelets in sessile-pedicellate pairs or triplets; disarticulation in the rames, below the sessile spikelets.
→ 22
22. Culms to 100 cm tall, often decumbent and straggling; terminal inflorescences composed of 2-6 subdigitately to racemosely arranged rames
Microstegium
22. Culms 40-600 cm tall, erect; terminal inflorescences panicles, with more than 6 primary branches; branches usuallywith 2 or more rames.
→ 23
23. Panicle branches alternate, with multiple rames; rames with more than 5 spikelet units
Saccharum
23. Panicle branches subverticillate, with 1-3 rames; rames with 2-5 spikelet units
Spodiopogon
17. All or most spikelet units heterogamous, usually also heteromorphic, sometimes the proximal units on the rames or racemes homomorphic and homogamous.
→ 24
24. Terminal inflorescences with elongated rachises.
→ 25
25. Rame internodes and pedicels with a translucent median line
Bothriochloa
25. Rame internodes and pedicels without a translucent median line.
→ 26
26. Sessile spikelets terete or laterally compressed, calluses usually sharp, sometimes blunt
Chrysopogon
26. Sessile spikelets dorsally compressed, calluses usually blunt, sometimes sharp
Sorghum
24. Terminal inflorescences and individual inflorescence units without elongated rachises, composed of 1-13 rames, or a raceme in which disarticulation occurs below the pedicellate spikelets.
→ 27
27. Inflorescences composed of rames, disarticulation being in the rame axes; rame internodes and pedicels with a translucent median groove
Bothriochloa
27. Inflorescences composed of rames, with disarticulation in the axes or a spikelike raceme (occasionally of 2 subdigitate spikelike branches) with disarticulation below the pedicellate spiklets; inflorescence internodes and pedicels without a translucent median groove.
→ 28
28. All spikelet units in the inflorescence heterogamous.
→ 29
29. Disarticulation occurring below the pedicellate spikelets, not in the inflorescence axes; pedicellate spikelets bisexual and awned, awns (4)6-15 cm long, pilose on the column, the hairs 1-2 mm long; sessile or subsessile spikelets staminate or sterile, unawned
Trachypogon
29. Disarticulation occurring below the sessile spikelets, in the inflorescence axes; pedicellate spikelets staminate, sterile, rudimentary, or absent, unawned or with awns to 6 mm long; sessile spikelets bisexual or pistillate, awned.
→ 30
30. Rames usually solitary on the peduncles, occasionally 2; rame internodes cupulate or fimbriate distally; lower glumes of the sessile spikelets veined between the keels
Schizachyrium
30. Rames usually 2-13 on the peduncles, occasionally solitary; rame internodes neither fimbriate nor cupulate distally; lower glumes of the sessile spikelets usually without veins between the keels
Andropogon
28. Basal spikelet units on each rame homomorphic and homogamous, sterile or staminate, unawned.
→ 31
31. Awns 5-15 cm long; rames with 3-10 homogamous spikelet units
Heteropogon
31. Awns 1-5(19) cm long; rames with 1-2 homogamous spikelet units.
→ 32
32. Inflorescences terminal on the culms, axillary inflorescences not present or few in number
Dichanthium
32. Inflorescences terminal and axillary, axillary inflorescences numerous.
→ 33
33. Homogamous spikelets distinctive, forming an involucre around the rame bases
Themeda
33. Homogamous spikelets not distinctive, not forming an involucre around the rame bases
Hyparrhenia
Source FNA vol. 25, p. 701. FNA vol. 25, p. 602. Author: Mary E. Barkworth;.
Parent taxa Poaceae > subfam. Panicoideae > tribe Andropogoneae > Zea Poaceae > subfam. Panicoideae
Sibling taxa
Z. diploperennis, Z. luxurians, Z. perennis
Subordinate taxa
Z. mays subsp. huehuetenangensis, Z. mays subsp. mays, Z. mays subsp. mexicana, Z. mays subsp. parviglumis
Andropogon, Apluda, Arthraxon, Bothriochloa, Chrysopogon, Coelorachis, Coix, Cymbopogon, Dichanthium, Elionurus, Eremochloa, Hackelochloa, Hemarthria, Heteropogon, Hyparrhenia, Imperata, Ischaemum, Microstegium, Miscanthus, Polytrias, Rottboellia, Saccharum, Schizachyrium, Sorghastrum, Sorghum, Spodiopogon, Themeda, Trachypogon, Tripsacum, Zea
Name authority L. Dumort.
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