Ancient tiny cobs and the evolution of Zea

If one hypothesizes that teosinte was domesticated to give us modern maize, it seems unexpected that very early cobs from many parts of the New World share less with teosinte than do later cobs. Many of the archaeobotanical specimens from Mexico, Belize, Costa Rica, Ecuador, Peru and Brazil studied over the past nine years have been extremely small with very reduced cupules and glumes very unlike those of teosinte (Fig. 1). The earliest available maize, from near Tehuacan, Mexico, have cupules 20-25 (34) mm long and lower glumes only 17-31 mm long. Cupule depths of 2-3000 year old maize from Costa Rica, Panama, Ecuador and Peru range only 4-12 mm. The oldest lowland maize, from Belize (1950-1000 B.C.), has similar ranges. Glumes of the earliest Peruvian maize are membranous and relaxed toward the ear base. No lower glumes of maize have the apical thickening (0.4-0.5 mm) of Zea mexicana, Z. luxurians and Z. diploperennis. No teosinte has the pith which is always found in maize cobs. The differences between teosinte and early maize are many, more than have generally been given.

Figure 1. Long sections of female alicoles of Balsas teosinte (Zea mexicana - El Salado population) and of early domesticated maize from Tehuacan, Mexico. The maize cob is a reconstruction using many measurements of Coxcatlan phase cobs, but the cupule dimensions fit many of the tiny cobs found elsewhere.

Robert McK. Bird

Please Note: Notes submitted to the Maize Genetics Cooperation Newsletter may be cited only with consent of the authors.

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