Annals of the Missouri Botanical Garden, 31: 301-315. (1944)
Geneticist to the Missouri Botanical Garden
Engelmann Professor in the Henry Shaw School of Botany of Washington University

1Much of the work reported in this paper was carried out while the author was a Fellow of the Guggenheim Foundation. Facilities for progeny tests were made available by the California Insti­tute of Technology and by the Blandy Experimental Farm of the University of Virginia. Grateful acknowledgement is made to these institutions, to Prof. Carl Sauer, who provided the material for ihe initial study, and to Dr. Isabel Kelly, who made most of the actual collections and supplied much critical information. As it stands, the paper is very largely due to her help and advice rhouch she is in no way responsible for its imperfections.

A remarkable kind of maize discovered in western Mexico by Dr. Isabel Kelly seems not to be known to maize experts, nor to have received any published mention, even of the most casual sort. This is certainly owing in part to the fact that with maize, as with other matters, western Mexico tends to be ignored. It may also reflect the fact that even in most of the area where we have studied this variety, a stranger interested in maize might travel for some time without meeting it in the market-place, the granary, or growing in the field.

In most of that area this maize is known as "maíz reventador" (literally "exploder corn", i.e. popcorn), so we shall refer to it by that name though in Jiquilpan and elsewhere in Michoacán it is known (if at all) as "maíz rosquera", and this name is current in parts of Jalisco as well. In the region around Purificación, Jalisco, the name "reventador" is used, though "pipitillo" is also employed, perhaps due to local hybridization with an imported variety of that name (see below). While maíz reventador is commonly used as a popcorn it is a completely different thing from the narrow-grained rice popcorns of central Mexico and bears only a general resemblance to the pearl popcorns of commerce.

Maíz reventador is small-grained, small-cobbed, flinty and undented (see fig. 1, table 1, and pls. 15 and 16). It is 12-16-rowed, with grains 6-7 mm. wide and about as high as they are wide. It is characteristically pure white, though red pericarp is well established in some localities. While yellow grains or occasionally all yellow ears are seen, all those which we have submitted to progeny tests showed obvious signs of having been crossed with other kinds of maize (see below). The husks are extremely tight and longitudinal compression lines can be seen running more or less the length of the ear, across the face of the kernels. The kernels are in straight rows, but the pairing of the rows is not evident, and since successive kernels in any row usually are of different shapes and frequently of different sizes they may be described as "tesselated" in contra distinction to those kinds of maize in which successive kernels in a row tend to be mechanically uniform in size and in shape.


Collection locality State Number
Row number Color
Chachahuatlan Jalisco 25 2.8-3.2-3.7 .7-1.0-1.3 .4-7-1.0 .3-.3-.4 10-14-16 White
Jiquilpan Michoacán 25 2.5-3.1-3.6 .5-1.0-1.3 .5-.7-1.0 .3-.3-.4 10-14-16 White
Coalcoman Michoacán 1 3.3 1.0 .7 .3 14 White
La Huerta Jalisco 2 3.1 1.2 .5-.7 .3-.4 14-16 White
Tenamaxtlan Jalisco 3 2.5-2.9-3.1 .7-.9-1.0 .6-.7-.7 .3-.3-.4 10-14-14 White (one red pericarp)
Ayotitlán Jalisco 4 2.9-3.1-3.5 .9-1.1-1.5 .7-.7-.8 .3-.3-.4 12-14-16 White
Culiacan Sinaloa 2 2.7 .8-.9 .7-.8 .3-.4 10-12 Tan pericarp
*Where three numbers are given the first is the lowest value in the collection; the next is the average (median); and the last is the highest.
All measurements are in centimeters.

The plant descriptions which follow are from end-season plants examined at Chachahuatlán, near Tuxcacuesco, Jalisco, Mexico, and from progeny tests grown at the Blandy Experimental Farm of the University of Virginia and at the experimental fields of the California Institute of Technology at Arcadia, California. It is known that many of the characters discussed below are affected by length of day, and it is probable that other factors such as night temperature are also important. This is particularly true of the date of maturing and number of tillers, two characters which are notoriously affected by place and time of planting.

1Kelly, Isabel, and Edgar Anderson. Sweet corn in Jalisco. Ann. Mo. Bot. Gard. 30:405-412. 1943.

Both at the Blandy Farm and at Cal. Tech. the plants of maíz reventador were extreme in their vegetative characters. They had narrower leaves with deeper channels above the midrib and with heavier midribs than any other varieties grown with them or studied previously at these laboratories. They bore more tillers, which were less differentiated from the main stalk, and they were later to mature. In Virginia they were not able to tassel before the growing season was stopped by frost, though other Jaliscan varieties managed to tassel if not to set seed, and maize from the highlands of Michoacán was only a little slower to mature than the local Virginia corn. In California they were later-seasoned than anything else in our cultures, much later than corn from Michoacán and a month later than sweet corn, "maíz dulce", from Jalisco.1 Furthermore, the yellow-grained maíz reventador, which was most certainly the result of crossing between white reventador and other varieties, was the earliest of these popcorns to mature, some of its plants being only a week later than the Jaliscan sweet corns. In Jalisco most maize is planted so late in the season, due to the dry winter and spring, that tillering is discouraged. However, from the results reported above we know that, given the proper conditions, maíz reventador is later-seasoned and has more tillers than any other maize which we have grown in our extensive tests.

The plant color of maíz reventador was also extreme, though similar to that of varieties grown by the Papago Indians and their relatives. There was no color on the upper leaves, but more or less of a dark mahogany-red was apparent on the exposed parts of the stem. On the leaves below the node bearing the ear there was no color on the blade except around the auricle, which was quite deeply marked with red on some plants. The sheaths of the lower leaves were evenly (and often brightly) colored with a clear red along the veins, even when they were not exposed to strong light. On some plants there was a slight deposit of color between the veins, but even on these plants the superficial aspect was that of red veins on a green background. The silks were uniformly green or a light sun-red that bleached out in the sun and could only be detected on cloudy days. The anthers were green or a very pale sun-red. There was a considerable and variable deposit of dull red on the glumes of the tassel. Five of the progeny tests of collected ears showed a heavy marking of red at the base of the glume (glume bar); one showed only a faint glume bar.

The tassels were long, slender, and wiry with small to average spikelets but very long branches. The lower internodes of the tassel were often extremely long, producing tassels of large size and low density. Most of the plants had 15 to 30 branches but there were a few with "ramosa-type" tassels which lacked a developed central spike and bore many short branches, decreasing in size towards the apex of the tassel.

The plants from the yellow-kerneled ears were similar in all the above characteristics, but were more variable and possessed numerous features characteristic of other kinds of Mexican maize. Some of them had bright red silks and tassels; most of them had a strong development of interveinal color on the sheaths of the upper leaves, and their tassel branch number, while extremely variable, was smaller (table II). As mentioned above, they were earlier-seasoned and had fewer tillers. All of these results would be expected if they were crosses between white maíz reventador and yellow Jaliscan sweet corns. Mr. Raymond Baker, who used one of these yellow ears in a cross, reports that sweet kernels segregated out in the second generation, practically proving this assumption.

Most of the variability in our collections of maíz reventador seems to be due to crossing with other kinds of maize, such as that just described with maíz dulce. Thanks to the interest of Sr. F. Vargas Tentory, we received maize collections from three forest clearings in the Coalcomán area of Michoacán ( (1) on Map 1). A variety very similar, if not identical, to maíz reventador was present in all three clearings, though in two of them it sometimes had a bright red pericarp. In two of the collections there were many obvious intermediates between maíz reveniador and larger-grained varieties. Similar collections have recently been received from the coast of Michoacán.

Resemblances.—The only variety closely resembling maíz reventador which has come to our notice is a series of ears presented by Ing. Taboada of the Dirreccion General, Secretaria de Agricultura y Fomento, to whom we are indebted for these and other favors. The ears presented by Ing. Taboada came from Culiacán, Sinaloa ( (14) Map 1), where they are known as maíz chapolote. They are quite similar to maíz reventador except that they look even more primitive and have a dark tan pericarp. The plants differ in being much shorter-seasoned. Maíz reventador is of particular interest because it is so much like a kind used in western Mexico in the Colonial period (see below). Two archeological occurrences are known, both excavated by Dr. Isabel Kelly, one at Paso Real, Jalisco ( (5)

Fig. I. Ear of Maíz reventador from Chachahuatlan, Jalisco, and shelled kernels from the same. Natural size.


Map 1. Distribution of maíz reventador: Solid black dots, regions where it is not grown and is apparently unknown; open circles, localities where maíz reventador or a very similar variety was collected or from which a similar, if not identical, variety is known from archeological investigation or historical documents. See the text (pages 309-311) for further details.

Map 1), on the Rio Armeria, downstream from Tuxcacuesco, and the other from Culiacán, Sinaloa (14). Both are only charred fragments of cobs but these are large enough for us to estimate kernel-size, cob-size, tesselation, and row number. If these charred fragments did not belong to maíz reventador, as here described, they must have belonged to some closely related small-cobbed, small-grained variety.

A detailed description of the fragments from Paso Real will be found in an appendix to Dr. Kelly's report on that area. Those from Culiacan were not received until that report was in press and are described here to put the facts on record.

As received for examination from the Museum of Anthropology of the University of California the material consisted of several carbonized cob fragments without kernels. The box bore the specimen number 3-6090, and Mr. Gifford's accompanying letter stated that it was Dr. Kelly's original number 46, from Culiacan, Sinaloa, Trench 2.

The largest fragment was an entire cross-section of a small cob, apparently from near the base. Since one of the smaller fragments was also basal, apparently at least two cobs were represented in the sample. The fragments were conspicuous by the small size of the spaces for the kernels, being slightly smaller than the smallest previously examined in this laboratory (Haury's material from Ventana Cave). The mid-cob width was 1.5 cm., the cob-kernel width was 2 mm. and the cob-kernel thickness was 2.8 mm. giving a cob-kernel area of 5.6 sq. mm.

The largest fragment is somewhat imperfect on one side and the row number cannot be absolutely determined. It is at least 14 and it might possibly be 18. There is no indication of the ear being elliptical, as in much primitive maize, and from the fragments one would judge the ears to have been cylindrical rather than tapering.

As a whole, the material is similar to that discovered by Dr. Kelly at Paso Real. It apparently was a small-grained flint, probably of the same general type as the small-grained popcorns or flints which are still to be found in western Mexico.

In a number of ways maíz reventador is quite similar to the remarkable maize grown by the Pima and Papago Indians, resembling it in plant color, narrow cobs, tesselated seeds, well-developed tillers, and prominent husk striations.

Most of the peculiarities of maíz reventador are to be found in an even more exaggerated degree in teosinte (Euchlaena mexicana). This is true of the narrow leaves, the slender stems, the tough roots, the late season, the wiry tassel, and the small seeds. The kernels of maíz chapolote from Culiacan are even of the same dark brown as teosinte. Furthermore, this variety has large knobs on every chromosome except No. 10. It would seem as if these western Mexican varieties represent a maximum introgression of teosinte. If so, this must have occurred at some time in the past. While teosinte is not unknown in western Mexico it is now a rarity in the fields where we have studied maíz reventador.

In a very general sort of way maíz reventador is somewhat similar to the maize varieties commonly grown in Jalisco. All of these varieties (known locally by such names as maíz criollo, maíz blanco, maíz colimato, maíz humeado, etc.) have a strong tendency to narrow, irregularly tapering ears, strongly appressed at the base, and to husk striations on the kernels (pl. 16, below). They have the general appearance of crosses between maíz reventador and other kinds of corn. To use a phrase employed by certain anthropologists, they probably contain maíz reventador "in solution." This assumption is at least partially confirmed when the variation in these varieties is examined plant by plant. If they have indeed resulted from crosses between maíz reventador and other kinds of maize, then the amount of maíz reventador germ-plasm (as well as its kind) should vary greatly from plant to plant, and we might expect to find occasional plants which have the maximum amount possible in that population ("reemergents," in the language of the physical anthropologists). Such plants should be very similar to maíz reventador. This is actually the case. In almost any corn crib in Autlán or Guadalajara or Ameca one will find occasional ears which show a strong resemblance to maíz reventador, much stronger than that of most Jaliscan maize. Much more rarely one may even come across a single ear which is almost within range of variation of maíz reventador itself.


Collection Locality State Plants
raised to
in mm.
Ears with small white kernels
K. 1 Sayula Jalisco 6 13-21-28 9 Heavy 0 0
K. 2 Talpa Jalisco 7 15-19-36 9 Heavy 0 0
K. 3 Mascota Jalisco 5 18-26-33† 10 Heavy 0 0
Sa. 22 Ayotitlán Jalisco 4 23-26-29 10 Faint 0 0
Ears with larger yellow kernels
K.4 Talpa Jalisco 5 12-13-29 12 Heavy 10 100
Sa. 11 Tenamaxtlán Jalisco 5 15-23-28 11 Heavy 40 40
*In the figures for number of tassel branches the middle represents the average (median) value; the others, the lowest and highest values.
†Excluding one plant with ramosa type tassel.

Some of our collections demonstrate the way in which maíz reventador tends to become incorporated with new varieties introduced into the region where it is grown. From the Purificación area, for instance, we have collections from Villa Vieja ( (7) Map 1) and from La Huerta. They demonstrate an apparent blending of reventador and a widely grown Mexican variety known as pipitillo. From Villa Vieja we have three ears which were being grown under the name of pipitillo and were said to be the common corn of that region. As a whole, they look more like reventador than like pipitillo as that name is commonly applied in other parts of Mexico (Guanajuato, Michoacán, Mexico, Morélos, etc.). However, as compared with pure reventador they are larger-grained, larger-cobbed, and with proportionately longer kernels. On closer inspection one of the ears (Pl. 16, extreme left, below) is enough like pipitillo so that it might pass under that name in a region such as the Los Altos zone of Jalisco where pipitillo is not as extreme in type as it is around Mexico City. It is not only outstanding for the characters enumerated above but it has kernels more or less dented; it has a conspicuous capping of starch and some of the kernels show a slight tendency to pointing (all of these being attributes of pipitillo). It would seem as if a genuine pipitillo, once introduced into this region, is now so swamped by repeated contamination with the local reventador that there are only traces of its original characteristics. This suspicion is confirmed by the collection from La Huerta (pl. 16, above) in the same general region. This consists of four ears, two of which are practically pure reventador and two of which have colored aleurone and slightly larger seeds. Significantly, they were identified locally as ''pipitillo (reventador)".

It seems not unlikely therefore that maíz reventador, or at least some very similar variety or varieties, is the foundation stock for the maize of western Mexico and the reason why the maize of that region is so distinctive as a whole. This conclusion is in accord with the archeological information reported above and with the evidence from a colonial document reported in the following section on distribution.

1Numbers in parentheses are from Map 1.

Distribution.— The known distribution of maíz reventador (see map 1) lends further weight to the above assumptions. From our own collections we know it to be widespread in western Jalisco, with collections from the Jaliscan plateau and from its southwesterly slopes and fringes. Specimens have been collected at Tenamaxtlan (10)1, Ayutla (10), Mascota (9), Talpa (8), El Limón (5), and Sayula (6). It is reported by several reliable informants from Ameca (11). We also have collections from Chachahuatlán (5) and Tuxcacuesco (municipality of Tuxcacuesco) (5), from Las Canoas and Ayotitlán (municipality of Autlán) (4), and from Villa Vieja (7), La Huerta and Pueblo Nuevo (Cuautitlán of older maps), all from the municipality of La Purificación as of 1943 (we are informed that this area is being redistricted). We have specimens from the old town of Tlajomulco (12) which are not quite typical and seem to have been mixed with modern commercial pearl popcorn. We have shelled corn sent from Tepic (13), Nayarit, and which was said to be grown near by. We also have specimens from Jiquilpan, Michoacán (2), on the border of Jalisco, and an ununusually reliable informant reports it as fairly common in those parts of Michoacán (3) which are adjacent to LaBarca, Jalisco.

Unfortunately, it is not possible to be as definite about regions where it certainly does not occur (or at least did not occur). In most of the areas studied its occurrence is now so casual that it can be found only after persistent search. In S. P. Tlaquepaque, near Guadalajara, it was not grown during 1943 but it is occasionally grown there, and within the memory of many inhabitants it was regularly grown by a few families. We have not collected it in the Los Altos zone of Jalisco, and several informants from that area did not recognize the name or sample cobs. In Guanajuato we are on firmer ground because of the extensive collections made by Dr. E. Limón of the Campo Agricola Experimental at Leon. He did not know it and nothing like it was represented in his collections. We are convinced that it does not now occur and has not recently been grown in the highlands of Michoacán (Cherán, San Lorenzo, Pátzcuaro, Uruapan) or in the region of intensive maize culture around Mexico City. In the collections of the Dirección General de Agricultura y Fomento at San Jacinto there are no ears even remotely like it from any of these regions and the specimen ears which we carried were viewed with equal astonishment by farmers, dealers, and agricultural experts. (In Jalisco, on the other hand, they were usually recognized, and the peculiar properties of the variety were described even in those towns where none was being grown in the current year.)

1Manuscript No. 50, T. III.
2"Ay rebentador que llaman; pequeno el grano, y blanco este porque abunda para pinole que lo asen tostando dicho Maíz y moliendo,lo y es el Bastimento corriente de la tierra, el qual toman batido en agua fria, lo reserban solo para esto" . There is (the kind) called popcorn, with little white grains, for this is abundant. They make pinole of it, toasting the aforesaid maize and grinding it up and it is the regular food stuff of the land, being eaten stirred up in cold water; they reserve it [popcorn] for this alone. [Spelling and punctuation somewhat modernized.]

In addition to its general resemblance to west-coast maize one reference suggests that maíz reventador was formerly widely distributed northward. In the Biblioteca del Estado in Guadalajara there is a manuscript copy1 of the 1776 Relación of (San Miguel de) Sahuaripa, (15) map 1, in Sonora, which describes a maíz "rebentador" with small white grains and says that in the form of pinole it was common provender of the area2.

We have several times referred to the casual occurrence of maíz reventador at present. It may be well to present in detail some of the actual facts on which this statement is based. In Tuxcacuesco (5) it is grown by a single family who pops it and sells popcorn balls locally. At Chachahuatlán several families grow a little of it, usually only one row or part of a row in their milpa (yellow maíz dulce is often grown in the same incidental way in an adjoining row which accounts for part of the yellow kernels). At Ameca (11) several reliable informants report it as being grown in this same way by a very few families. In Jiquilpan, Michoacán (2), two families make a regular practice of selling popcorn balls in the local markets and on the street outside their houses. They grow a little themselves and occasionally buy additional ears. In Tiajomulco (12), in 1943, it was grown by only one family who had 15 or 20 plants along one edge of their corn field.

In questioning informants as to where it might be obtained we have often (Ameca is one exception) met with the statement that more of it was being grown up in the hills ("en cl cerro"). Questions as to why it was more frequent in the hills met with a variety of answers ("more water", "better soil", "better drainage", etc.). We suspect that if it is indeed commoner in the hills, as has been so frequently reported, it is there because it is an ancient kind of maize and like many other ancient things it survives longest in out-of-the-way places.

1Kelly and Anderson. loc. cit.

Uses.—Maíz reventador is used at the present time for popcorn and for pinole, though the latter is made from other varieties of maize as well.1 Sometimes the popcorn is sold as loose grains, with or without sugar or salt, but more frequently it is made into balls by the addition of panocha (crude brown sugar) syrup. These are variously known as chivitas, palomitas, and rosqueras (the names also used in other parts of Mexico when other kinds of maize are use for popping). In Jiquilpan, Michoacán, the unpopped grains are used in the manufacture of thin sweet cakes, locally known as ponteduro. This confection can be made with a variety of materials and is usually prepared as loose, sugar-coated grains.1

Directly, maíz reventador would seem to be of very limited economic importance. As a popcorn it seems to be inferior to modern commercial varieties. Indirectly, however, it may be of great potential importance. Modern maize breeding is now at the point where it is beginning to improve commercial varieties by planned crosses to bring in desirable characters. For such a program maíz reventador has a great deal to offer. It has tough stalks and a tough strong root system. The hard-surfaced leaves and stems are resistant to insect attack and it has tight, tough husks which protect the ear. Some of these qualities may prove useful in creating the maize of the future.


  1. Though previously unmentioned in maize literature, maíz reventador is widely, if not commonly, grown in western Mexico. Its prevalence in out-of-the-way places, as well as its close resemblance to the charred remains of prehistoric maize from western Mexico, suggests that it was once a staple crop there. Further confirmation for this suggestion is given by the general resemblances of commercial varieties in the west of Mexico to maíz reventador, by the appearance of occasional plants which resemble it even more closely, and by the description of the same or a similar maize in a manuscript of 1776.
  2. Maíz reventadar is described in detail. It is outstandingly slender, in cob, leaf and stem; it has tough, strong leaves, stems, and roots. Plant color, when strongly developed, is chiefly along the veins of the leaves rather than between them.
  3. It is used locally for confections (pinole and popcorn balls).
  4. Several of its outstanding characteristics make it important in modern maize-breeding programs.