Sometime in the last four decades, teosinte appeared a few kilometers southwest of Texcoco (state of Mexico, Mexico). Today it is a flourishing, though limited, population creating problems for local farmers. I first saw it last summer while traveling the new Texcoco-Mexico City highway across what used to be Lake Texcoco -- it was abundant along the flanking fence for about two kilometers. Since then during weekend outings I have collected it at many places in the area from Colonia Netzahualcoyotl (a.k.a. Boyeros) north to San Andrés Riva Palacio.

Plants of this teosinte are 1.0-3.0 m tall and have 3-9 ear branches; rarely is there a tiller or branch low on the stem. The uppermost ear branch usually is at the penultimate leaf-bearing node. The next-to-last ear branches vary greatly -- 2-95 cm long. The longer branches have terminal tassels; these and the main tassel vary in the abscission of their rachids, 40-100%. Ear rachids from one typical plant range 5.4-8.0 mm long, 2.5-3.9 mm wide and 2.9-5.2 mm thick (rachid weight: 40-108 mg). In the population ear rachid weights vary considerably: the range of means for 4 plants with especially small rachids is 64-75 mg, while large-rachid plants range 124-136 mg.

There is some evidence of mutual introgression with maize. I and friends have collected some very small ears, each with a balance of teosinte and maize cob traits. There are some earlets on teosinte-like plants with two spikelets per segment, reduced abscission, and/or thickened cob rachises. Associated maize ears are often quite small with small, flinty kernels.

There is one collection of Netzahualcoyotl teosinte in the CIMMYT Maize Germplasm Bank (accession 13588), from San Felipe, collected by H. G. Wilkes and T. A. Kato Y. in 1992. J. Jesús Sánchez G. and Lorenzo Ordaz S. (El Teocintle en Mexico, 1987) cite two collections from this population in the INIFAP (Mexican national agricultural) germplasm bank, one made by them and one by John Doebley. All have been classified as part of the Chalco race, but some plants and ear segments seem too small for that race. I will place several samples of seed in the INIFAP and CIMMYT germplasm banks.

I have found scattered plants on the shoulder of the Texcoco-Vera Cruz highway and in the center of Texcoco. Wilkes, Sánchez and Ordaz say that teosinte in the Valley of Mexico occurs exclusively in maize fields, but in several places Netzahualcoyotl teosinte is found on the shoulders of roads and the banks of irrigation ditches in competition with grass and large broadleaf weeds. In some of the small ejido corn fields with teosinte there is five times as much teosinte as maize, making for poor and difficult harvests. Some corn is cut as forage but most is cut later for fodder; teosinte is often included. Because most of the resulting manure is placed on fields, teosinte seed are being spread over an ever wider area. Informants know of this cycle and add that irrigation water is a factor. Several informants, including Sr. Guadalupe Guevara (retired maestro of CIMMYT's Maize Germplasm Bank), have told me that teosinte appeared in their fields within the last 8-40 years. Perhaps it came in a cow brought from Chalco or Michoacán, maybe with purchased fodder. Maybe it spread from an observation plot at one of the local agricultural institutions. 

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