Zea L.
Zea (zeia), old Greek name for a food grass, possibly spelt.
Including Mays Miller, Mayzea Raf., Reana Brignoli, Thalysia Kuntze. = Zea mays subsp. mays
Excluding Euchlaena, Teosinte (see comments)
Habit, vegetative morphology. Robust annual. Culms 200–450 cm high; herbaceous. Culm nodes glabrous. Culm internodes solid. Leaves not basally aggregated; non-auriculate. Leaf blades broad; flat; without cross venation; persistent; rolled in bud; a fringed membrane.
Reproductive organization. Plants monoecious with all the fertile spikelets unisexual; without hermaphrodite florets. The spikelets of sexually distinct forms on the same plant (male and female); female-only and male-only. The male and female-fertile spikelets in different inflorescences. The spikelets overtly heteromorphic. Plants outbreeding.
Inflorescence. Inflorescence peculiar: the female axillary, comprising a stout, spicate spadix with spikelets in few to several longitudinal rows, terminating in a tuft of long pendulous styles (’silks’); the male spikelets in terminal panicles of spiciform ‘tassels’; spatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets paired; not secund; consistently in ‘long-and-short’ combinations (male), or not in distinct ‘long-and-short’ combinations (female).
Female-sterile spikelets. Male spikelets in pairs, two-flowered, with many-nerved, membranous glumes. Lemmas and paleas hyaline, the florets with three stamens and two cuneate lodicules. Rachilla of male spikelets terminated by a male floret. The male spikelets with glumes (two); without proximal incomplete florets; 2 floreted. The lemmas awnless. Male florets 2; 3 staminate.
Female-fertile spikelets. Spikelets not noticeably compressed to compressed dorsiventrally; not disarticulating. Rachilla terminated by a female-fertile floret. Hairy callus absent.
Glumes two; more or less equal; long relative to the adjacent lemmas; not pointed; awnless; similar (basally fleshy, hyaline above). Lower glume not pitted; relatively smooth; 0 nerved. Upper glume 0 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 1; paleate, or epaleate. Palea of the proximal incomplete florets when present, fully developed to reduced. The proximal incomplete florets sterile. The proximal lemmas awnless; 0 nerved; more or less equalling the female-fertile lemmas to decidedly exceeding the female-fertile lemmas; similar in texture to the female-fertile lemmas (hyaline); not becoming indurated.
Female-fertile florets 1. Lemmas less firm than the glumes; not becoming indurated; awnless; hairless; non-carinate; 3 nerved. Palea present; relatively long; apically notched; with apical setae; not indurated (papery at base, hyaline above). Lodicules absent. Stamens 0. Ovary glabrous. Styles fused (fused nearly to tip). Stigmas 2 (at tip of style); white to red pigmented (or green).
Fruit, embryo and seedling. Fruit medium sized; compressed dorsiventrally, or not noticeably compressed. Hilum short. Embryo large. Endosperm hard; without lipid; containing only simple starch grains. Embryo without an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins overlapping.
Seedling with a long mesocotyl. First seedling leaf with a well-developed lamina. The lamina broad; curved.
Abaxial leaf blade epidermis. Papillae absent. Mid-intercostal long-cells having markedly sinuous walls. Microhairs present; panicoid-type; without ‘partitioning membranes’ (Zea mays); (39–)42–51(–55) microns long; (8.4–)9.6–11.4(–12) microns wide at the septum. Microhair total length/width at septum 3.4–5.4. Microhair apical cells (21–)32–38 microns long. Microhair apical cell/total length ratio 0.5–0.73. Stomata common; (39–)42–48(–60) microns long. Subsidiaries triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; silicified. Intercostal silica bodies vertically elongated-nodular, or cross-shaped. Costal zones with short-cells. Costal short-cells conspicuously in long rows, or neither distinctly grouped into long rows nor predominantly paired. Costal silica bodies ‘panicoid-type’; cross shaped; not sharp-pointed.
Transverse section of leaf blade, physiology. C4; biochemical type NADP–ME; XyMS–. PCR sheath outlines uneven. PCR cells with a suberised lamella. PCR cell chloroplasts with reduced grana; centrifugal/peripheral. Mesophyll with radiate chlorenchyma. Leaf blade adaxially flat. Midrib conspicuous; having a conventional arc of bundles; with colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups; in simple fans (the groups large-celled - ‘Zea-type’). Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present; nowhere forming ‘figures’. Sclerenchyma all associated with vascular bundles.
Culm anatomy. Culm internode bundles scattered.
Phytochemistry. Leaves containing flavonoid sulphates (Z. mays). Leaf blade chlorophyll a:b ratio 4.37.
Special diagnostic feature. Fruiting inflorescence a massive, axillary, spatheate cob with a spongy axis, the fruits in many rows.
Cytology. Chromosome base number, x = 10. 2n = 20. 2 ploid. Chromosomes ‘small’. Haploid nuclear DNA content 2.4–5.5 pg (6 values for Z. mays, mean 4.4). Mean diploid 2c DNA value 5.2 pg (values from 4.4 to 11.0 given for Zea mays by different authors). Nucleoli persistent.
Taxonomy. Panicoideae; Andropogonodae; Maydeae.
Distribution, ecology, phytogeography. 1 species; unknown in the wild: originated in tropical America, cultivated in all warm to tropical regions of both hemispheres. Mesophytic.
Neotropical. Caribbean, Venezuela and Surinam, Amazon, Pampas, and Andean.
Hybrids. Intergeneric hybrids with Euchlaena (×Euchlaezea Janaki ex Bor), Saccharum, Tripsacum.
Rusts and smuts. Rusts — Physopella and Puccinia. Smuts from Ustilaginaceae. Ustilaginaceae — Sphacelotheca and Ustilago.
Economic importance. Cultivated fodder: Zea mays. Grain crop species: Z. mays (Maize, Corn, Mealies).
References, etc. Leaf anatomical: Metcalfe 1960; this project.
Special comments. The descriptions of maize relatives require updating, to conform with modern taxonomic views (e.g. Doebley and Iltis 1980, Iltis 1987). The older and convenient but artificial treatment, separating the readily distinguishable Zea mays subsp. mays from the rest, is retained here pending acqisition of detailed comparative morphological data.
Illustrations. • Pollen antigens. • Transverse section of leaf blade, transmission electron micrograph. Zea mays. C4 type NADP-ME. • Pollen antigens. • Pollen antigens: cross-reactions against anti-Lolium serum. • Heat stable pollen antigens (allergens): cross-reactions against anti-Lolium serum. • Pollen antigens: cross-reactions against anti-Cynodon serum. • Pollen antigens: cross-reactions against anti-Zea serum. • Pollen antigens: cross-reactions against anti-Zea serum
Cite this publication as: Watson, L., and Dallwitz, M. J. (1992 onwards). ‘Grass Genera of the World: Descriptions, Illustrations, Identification, and Information Retrieval; including Synonyms, Morphology, Anatomy, Physiology, Phytochemistry, Cytology, Classification, Pathogens, World and Local Distribution, and References.’ http://biodiversity.uno.edu/delta/. Version: 18th August 1999. Dallwitz (1980), Dallwitz, Paine and Zurcher (1993 onwards, 1998), and Watson and Dallwitz (1994), and Watson, Dallwitz, and Johnston (1986) should also be cited (see References).
