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Revista de Biología Tropical

On-line version ISSN 0034-7744

Rev. biol. trop vol.47 n.3 San José Sep. 1999

 

Weeds as a source for human consumption. A comparison between tropical
and temperate Latin America
 
 
Martha Díaz-Betancourt1, Luciana Ghermandi2, Ana Ladio2, Ismael R. López-Moreno1,
Estela Raffaele2  and Eduardo H. Rapoport 2,3
 
 
 

 

Received 16-IX-1998. Corrected 15-II-1999. Accepted 22-II-1999.
 

Abstract

Weeds abound in urban and agricultural environments. Depending on region and site, up to 66% of weed species are edible, and may constitute an additional food source for humans. Based on 400 samples, ¼ m2 each, collected in tropical areas (e.g., roadsides, urban vacant lots, streets, sugar cane and coffee plantations in Coatepec, Mexico), average figures of edible fresh biomass vary between 1277 and 3582 kg/ha. A similar survey performed in a temperate area (739 samples in Bariloche, Argentina) showed mean values between 287 and 2939 kg/ha. A total of 43 species were sampled in Coatepec and 32 species in Bariloche. The general means were 2.1 and 1.3 tons/ha, respectively. At a greater geographic scale, a comparison between Mexican and Argentine weeds shows that, proportionately, the food parts vary a little between regions. In general, from higher to lower, the order of uses goes from leaves, seeds, roots, fruits, herbals, flowers and condiments. Edible roots (including bulbs and rhizomes) appear to be more common among perennials than among annuals.

Key words

Argentina, Bariloche, Coatepec, edible weeds, food plants, gathering, Mexico, Patagonia, urban flora.
 

 
Although plants have sustained the hunting and gathering peoples since the Paleolithic, the prevailing knowledge about edible species began to be lost since the invention of agriculture in the Neolithic. Two well-preserved mummies found in Denmark, provided interesting information on food habits during the Iron Age. Their last meals contained 66 different plant taxa (Godwin 1960; King 1966), i.e., a diet much more diversified than that of modern man. According to FAO’s Production Yearbooks, developed countries, and especially urban populations, began to depend almost entirely on the extensive and intensive agricultural production consisting in merely a little more than 100 food plants. Part of the old tradition is still maintained in some Latin American and eastern Asian countries. In Mexico, more than 20 "weeds" are also cultivated (Linares and Aguirre 1992). For instance, in Korean local markets 112 wild plants are sold at prices higher than those of cultivated species. Moreover, eleven species (some of them "weeds") are exported to the U.S.A. and used to prepare Korean and Chinese typical dishes (Pemberton and Lee 1996). Similarly, Moroccan weeds are exported with the same purpose to the U.S.A., Spain, Italy and Greece (Tanji and Nassif 1995).

The use of edible wild plants and weeds has been considered by several authors (Harris 1969, Kunkel 1984, Facciola 1990, Zurlo and Brandão 1990, Duke 1992, Linares and Aguirre, eds. 1992, and references there). Some of these books only provide extensive lists of species, with indications of their edible parts, while others add descriptions and illustrations of the species. Clarke (1977), Michael (1980), and Linares and Aguirre (1992) include numerous recipes. Edible weeds, however, are scarcely used in many countries, and weed gathering is more of a weekend hobby than a regular source of food supply.

To our knowledge, no attempts have been made to assess quantitatively the potential amount of food provided by common weeds and escapes.

Our interest was to evaluate the available biomass of human food provided by weeds in urban, periurban and field habitats in the northern and southern Neotropical region. We tried to compare two samples obtained in different climatic regions, i.e., tropical (Coatepec, Mexico) and temperate to cold-temperate (Bariloche, Argentina) areas.

 
 
Materials and methods

The environments selected were abandoned fields, main (paved) roads, secondary roads (suburban dirt roads), pathways, vacant urban and suburban lots. Sugar cane fields, milpas, coffee plantations (only Coatepec), and orchards (only Bariloche) were also considered. In these cases, we gathered and weighed all the edible parts of species appearing in 0.25 m2 quadrats (50 x 50 wooden frames). Along roadsides (haphazardly selected), we sampled at repeated 1 km distances, by laying ten quadrats regularly at 2 m distance each, parallel to the pavement. Urban vacant lots and fields were randomly sampled. The frames were laid along a random walk using a stopwatch to select compass direction and number of steps. The collected plants of each sample were kept in plastic bags and transported to the laboratory, separated by species and their edible portions were weighed with 0.01 g precision. Water content was calculated after 72 hr dehydration at 60-80 º C (Rapoport et al. 1995). Additionally, in some cases, the yields were assessed in terms of biomass collected per minute of harvesting. This survey was performed in order to evaluate whether there is any profit in gathering a given species in sites where it is abundant. In this way, we were in the position of a person searching for food. The analysis of the proportions of edible parts (roots, leaves, fruits, seeds) of all Mexican and Argentine weed species was obtained from Kunkel’s (1984) list, and from our own records. Comparisons of fresh edible weights among habitats were made by means of Kruskal-Wallis tests. The comparison of total fresh weights between Mexico and Argentina was made by means of a Mann-Whitney test. In the case of significant differences, the Student-Newman-Keuls’ test of multiple comparisons was applied. The detailed statistical analysis of data is reported elsewhere (Ladio et al. 1998).

The main roads sampled in Bariloche were roads No. 258 (Bariloche-El Bolsón), No. 237 (Bariloche-Alicura and Bariloche-Airport) and No. 237 (Bariloche-Llao Llao). In Coatepec, the road sampled was Carretera Briones.

 
Climate

Comparative data on climates appear in Table 1.

 

TABLE 1
Comparative characteristics of both areas
 
 
COATEPEC
BARILOCHE
Altitude
1,252 m
750 m
Latitude
19º27º N
41º 08’ S
Longitude
96º 57º W
71º 08-71º 36’ W
Mean annual precipitation
2250 mm*
1000 mm**
Mean annual temperature
18.8º C
8.4 ºC
Coldest month mean temp.
15.2º(Jan.)
2.3º (July)
Hottest month mean temp.
21.4 ºC (May & June)
14.5 ºC (Feb.)
Extreme temperature
3.9 to 33.5 ºC
-18 to 35.5 ºC
Prevailing winds
N & NW (winter), E, S & SE 
(spring, summer & fall)
W
Climate
A C (fm) w"a(i’)g
GCs lk (Mediterranean regime)
Population
40,000
100,000
Source
Gómez and Soto 1990
Rudloff 1981; Grigera et al. 1989; UNC 1983
 * Rains all year round, although more intense in summer.
 ** Rains and snow, with maximum precipitation in winter. Precipitation varies from 800 mm in the eastern to 1.600
          mm/yr in the western parts of the city.
 
 
Results

The majority of the sampled species appear in Kunkel’s (1984) list of food plants, to which we added Osmorhiza chilensis, from Argentina, and Drymaria gracilis, Galinsoga quadriradiata, Hydrocotyle bonariensis, Hydrocotyle mexicana, Margaranthus sulphureus, Oxalis latifolia, Sida glabra, S. spinosa, and Tripogandra, serrulata from Mexico. These plants are commonly consumed by people and were repeatedly tasted by us.

In total, 43 species were recorded in Coatepec and 32 species in the Bariloche samples (Tables 2 and 3). They represent, however, a small fraction of the real richness in both areas. More than 24% of the 700 weeds listed in Mexico by anonymus (1991) are edible. Of the 320 exotic weeds recorded in northwestern Patagonia (Rapoport and Brión 1991), 90 species (28%) are edible. The Catalogue of Mexican Weeds (anonymus 1991) includes 168 edible species of which 36.3% are perennial and 63.7% annual and/or biennial. Similarly, in Argentina, the proportions are 35.0% and 65.0%, respectively, from a total of 160 edible weeds that are mentioned in Marzocca et al. (1976). Perennials show a significantly higher proportion of edible roots (including tubers or rhizomes) and herbals than among the annual-biennial species (P = 0.027 and 0.021, respectively; Table 4). In contrast, annual-biennials show a greater proportion of edible leaves and seeds than perennials (P = 0.008 and 0.012, respectively) as showed by means of a 2 x 2 contingency table.

 

TABLE 2
Coatepec, Mexico. Mean available food (fresh weight in grams) per 0.25 m2 sample and frequencies (number of times
each species was found in 100 samples); SD = standard deviation
 
 
 Species
Vacant lots
Dirth roads & pathways
Plantations
Highways
mean 
weight
S.D. freq.
mean 
weight
S.D. freq.
mean 
weight
S.D. freq.
mean 
weight
S.D. freq.
Acalypha wilkesiana
-
-
-
-
-
-
6.68
6.17
7
1.57
1.01
5
Amaranthus dubius
0.93
1.02
3
50.60
49.45
3
0.40
0.00
1
-
-
-
Amaranthus hybridus
30.71
34.22
6
6.53
5.29
3
-
-
-
17.63
27.05
14
Amaranthus spinosus
6.10
5.32
8
47.68
0.00
1
-
-
-
-
-
-
Anagallis arvensis
1.23
0.90
2
0.84
0.46
4
0.27
0.00
1
2.35
1.62
8
Bidens odorata
9.32
10.36
30
5.20
6.26
24
5.69
5.97
14
5.86
7.57
31
Brassica rapa
-
-
-
-
-
-
3.07
2.30
4
-
-
-
Canna indica
-
-
-
16.23
0.00
1
-
-
-
-
-
-
Chenopodium ambrosioides
-
-
-
59.32
0.00
1
4.03
0.00
1
13.29
0.00
1
Commelina diffusa
5.77
5.44
48
5.16
6.66
43
11.19
14.76
59
45.20
56.56
59
Commelina erecta
20.90
14.25
3
12.21
6.82
5
34.67
46.29
40
-
-
-
Drymaria cordata
5.32
6.65
27
1.31
1.46
15
5.92
7.73
24
0.92
0.45
2
Drymaria gracilis
7.04
6.71
9
6.54
9.46
12
3.45
8.18
10
34.66
74.19
27
Galinsoga quadriradiata
6.46
7.74
20
2.95
2.83
26
7.15
10.88
17
14.20
15.61
42
Heliconia caribaea
-
-
-
342.81
204.63
3
-
-
-
-
-
-
Hydrocotyle bonariensis
13.95
17.83
19
1.30
1.06
13
6.57
4.16
3
-
-
-
Hydrocotyle mexicana
1.99
1.56
3
7.38
11.24
9
-
-
-
-
-
-
Ipomoea purpurea
-
-
-
-
-
-
-
-
-
5.08
4.83
16
Ipomoea tilliacea
-
-
-
-
-
-
-
-
-
5.09
4.38
7
Ipomoea triloba
4.04
5.58
23
7.62
11.94
8
7.09
6.95
3
6.42
4.39
7
Margaranthus sulphureus
6.72
7.87
6
-
-
-
-
-
-
-
-
-
Oxalis corniculata
1.97
2.86
40
2.79
4.18
43
2.14
1.91
34
2.60
3.96
42
Oxalis latifolia
1.70
1.61
14
4.92
5.75
17
9.28
16.28
45
3.43
4.87
20
Phaseolus vulgaris
-
-
-
-
-
-
-
-
-
0.70
0.26
10
Piper auritum
-
-
-
23.92
0.00
1
-
-
-
35.99
24.18
2
Plantago hirtella
-
-
-
1.75
1.09
3
-
-
-
3.35
0.00
1
Plantago lanceolata
-
-
-
158.62
0.00
1
-
-
-
-
-
-
Portulaca oleracea
-
-
-
-
-
-
10.38
0.00
1
0.61
0.26
2
Rumex obtusifolius
25.57
27.19
10
15.66
9.64
10
26.26
29.43
18
25.70
19.68
11
Sida acuta
-
-
-
-
-
-
2.09
1.59
2
-
-
-
Sida glabra
1.33
0.00
1
-
-
-
-
-
-
-
-
-
Sida rhombifolia
5.78
7.02
49
4.37
2.19
17
-
-
-
3.74
4.51
14
Sida spinosa
2.87
2.26
10
14.05
12.59
8
5.41
6.87
4
-
-
-
Solanum nigrum
3.75
3.62
3
9.70
0.00
1
-
-
-
-
-
-
Sonchus oleraceus
8.99
2.05
2
22.13
14.96
3
-
-
-
-
-
-
Spilanthes americana
10.24
10.75
34
13.52
23.17
20
15.65
14.97
30
12.68
17.63
32
Tagetes micrantha
-
-
-
-
-
-
-
-
-
11.63
0.43
2
Taraxacum officinale
0.39
0.00
1
-
-
-
-
-
-
6.41
5.61
4
Tradescantia fluminensis
0.20
0.00
1
62.58
50.66
2
2.69
2.48
3
75.66
97.45
33
Trifolium repens
-
-
-
2.51
3.29
14
-
-
-
8.39
7.19
5
Tripogandra serrulata
13.27
28.39
22
10.71
13.54
11
20.88
20.08
55
-
-
-
Xanthosoma robustum
16.53
15.85
10
14.48
16.79
10
18.68
13.15
7
10.08
8.30
7
Youngia japonica
6.73
14.67
15
3.19
2.64
9
3.33
3.53
19
2.94
10.68
17
 
 
 


 
 
 

TABLE 4
A comparison of food parts in Mexican (168 species) and Argentine (160 species) weeds.
 
 
 
México
Argentina
 
Perennials
(%)
Annuals/ Biennials
(%)
Perennials
(%)
Annuals/ Biennials (%)
Roots, rhizomes
15.4
7.7
19.1
8.0
Leaves, stems, buds
30.7
44.0
41.2
54.0
Flowers
4.4
3.5
8.8
4.3
Fruits
13.2
10.5
8.8
2.2
Seeds
19.8
26.6
11.8
24.8
Condiments
4.4
2.8
4.4
5.1
Herbals (tea,coffee)
12.1
4.9
5.9
2.2
 
 

Yields per hectare: Because the number of sites surveyed and the number of samples per site were numerous, we made a tentative assessment of the amount of food available per hectare (Table 5). In the case of plantations and orchards, cultivated plants were not included. Coatepecan yields (2.1 tons, on average, per hectare) were apparently higher than the Barilochean yields (1. 3 tons per hectare). The extreme maximum yield was recorded on a main road between Coatepec and Xalapa (10,158.0 kg/ha) based on 10 samples taken in January 1996, and on a vacant lot in Bariloche (7,542.9 kg/ha) based on 7 samples taken in December 1996. When comparing equivalent Coatepecan and Barilochean environments by means of a Mann-Whitney test, the differences were not significant (P>0.05). However, the differences in the median values among total yields per hectare of Mexico and Argentina were significant (U = 880; P = 0.03)
 

TABLE 5
Assessment of available food per hectare
 
Coatepec
No. samples
(0.25 m2)
Mean fresh weight 
yield (kg/ha)
 
sd
Plantation (coffee, 
sugar cane)
100
2031.3
1285.2
Urban & suburban 
vacant lots
100
1277.1
663.5
Streets and pathways
100
1453.4
1441.1
Main roads
100
3582.4
3051.0
       
Bariloche      
Abandoned fields
80
287.2
219.2
Urban & suburban 
vacant lots
193
1253.5
392.8
Orchards
65
2938.8
3064.0
Streets and pathways
191
1008.0
524.0
Main roads
210
1326.6
460.0
 
 

Gathering harvest. Species’ yields: The following data correspond to fresh weights of the edible parts obtained per species in a given period of time. Sites were selected for their special abundances, from the point of view of a person searching for food. The process of gathering in Mexico took 15 minutes for each sample (five samples per species) and the mean values are presented per minute (Table 6).
 

TABLE 6
Food yield (g) per minute in Coatepec, Mexico. Mean
values based on 5 samples.
 
 
Species
Coffee 
plantations
Sugar cane 
plantations
Dirt roads
Vacant lots
         
         
Bidens odorata
-
5.3
-
-
Commelina diffusa
11.8
12.8
13.8
-
Commelina erecta
18.2
-
-
-
Drymaria gracilis
14.6
10.8
-
-
Galinsoga quadriradiata
2.3
-
-
-
Heliconia caribaea
-
-
110.2
-
Hydrocotile bonariensis
4.8
-
-
1.7
Hydrocotyle mexicana
-
-
4.0
-
Oxalis latifolia
-
-
4.5
-
Rumex obtusifolius
23.8
-
37.8
-
Sida rhombifolia
-
-
-
5.0
Spilanthes americana
5.2
4.9
-
6.0
Xanthosoma robustum
33.2
29.4
15.0
21.6
 

In Bariloche, only three species were evaluated. (i) Taraxacum officinale (8 sampling sites, 21 minutes total gathering time). Depending on its abundances, yields varied between 9.1 and 36.4 g/min, with a mean of 17.0 ± 8.8 g/min. (SD) of leaf blades without their central nerves. (ii) Chenopodium album (3 samples, 9 minutes gathering time). Yields were from 38.3 to 56.3 g/min, with a mean of 48.0 ± 9.1 g/min. Only leaves and tender apical stems were considered. (iii) Montia perfoliata (11 sampling sites, 40 minutes total gathering time). Yields from 31.0 to 239.6 g/min, with a mean of 80.4 ± 65.0 g/min. Leaving aside the figures obtained in Heliconia caribaea, which represents a special case for its edible roots, yields seem more productive in Bariloche than in Coatepec. Outstanding biomasses are produced by Montia perfoliata, a North American invader of Patagonian urban forests.

The most profitable plants in Bariloche: Montia perfoliata (=Claytonia perfoliata)

This species shows clear capabilities to recover after harvesting. During the 1995 growth season, in Bariloche we measured the fresh biomasses of three 0.25 m2 plots completely dominated by M. perfoliata. The procedure was repeated on the same plot ca. 30 and 60 days later, with the following results (in grams).

 

 
October
November
December
Totals
Plot A
138.6
115.1
22.3
276.0 g.
Plot B
487.9
141.9
96.7.
726.5 g.
Plot C
381.0
398.6
48.5.
828.1 g.
 

 
On the basis of 34 samples where M. perfoliata was abundant, food biomasses varied from 108.5 to 973.6 g per 0.25 m2 plot. Mean value 275.9 ± 210.6 g (SD). The aerial parts of this plant are 100% edible. Average water content varied around 78.5 ± 7.3 %.
 

Plantago lanceolata
Leaf fresh weight per 0.25 m2 plots (n = 25 plots) showed figures ranging from 39.2 to 309.2 g. Mean value 124.1 ± 60.2 g. Seeds should be added to this food source. At the end of the summer, we selected three 1 m2 plots showing ripe fruits. On average, there were 356.0 ± 38.4 spikes/m2 in high density patches. Each spike may contain about 500 seeds measuring 2 mm each, showing about 36 % abortions. Viable seeds were assessed in 162.1 g/m2. Although the process is laborious (about one hour-person to screen the seeds of one square meter), it is useful to know that a one hectare monospecific plot may yield more than 1.5 tons of seeds, in addition to almost 5 tons of leaves. Of course, it would imply the design of adequate mechanical technology to accelerate the process of screening seeds. Average water content of leaves varied around 78.6 ± 4.9 %.

 

 

Rumex acetosella
Yields vary between 8.9 and 186.7 g/0.25 m2. Mean 53.3 ± 47.9 g (n = 15 samples). The species is widely distributed in disturbed and undisturbed habitats, especially in surrounding grasslands and pasturelands. Average water content varied around 77.1 ± 4.6 %.

Taraxacum officinale
Yields vary between 11.2 and 107.4 g/0.25 m2 (central ribs excluded). Mean 47.2 ± 27.6 g (n = 17 samples). Average water content varied around 82.2 ± 4.7 %.
 

 
Discussion

Common weeds prove to be an interesting resource in small to medium-sized human settlements where they may provide supplementary food. In large cities, suburban populations may also profit from edible weeds. The data from Table 7 show that edible, non-weedy plants comprise between 6 and 21 percent of the biomass of the natural communities surveyed. The proportion of edible plants increases considerably in anthropic environments, especially in weed communities. Roughly, ten percent of the 260,000 known vascular species of the world should be considered as a potential source for human consumption. It is probably not by mere chance that the majority of the centers of origin or domestication of cultivated plants proposed by Vavilov (1938) corresponded to ancient, sedentary cultures. The idea that civilizations arose in areas with abundant edible plants adequate for culturing is probably incorrect. Since edible plants abound everywhere, it seems that civilizations developed in any environment where for historical reasons, people had time enough to exploit their natural resources in a more permanent and intensive way. By selection, plants originally wild, began to be more productive and adequate for human consumption. Rye, oats, carrots and several other cultivated plants originated as weeds, a fact that gives a clear idea of the enormous potential of weeds and other wild non-weedy plants as a source for new cultures. The economic incentive provided by the revival of ancient gastronomic traditions persuaded some private entrepreneurs to change from the occasional gathering to a more permanent cultivation of "weeds". Popular markets in Mexico (Linares and Aguirre 1992) and Korea (Pemberton and Lee 1990) offer a variety of gourmet "weeds" at higher prices than the common vegetables.

A case of human-livestock-plant mutualism is mentioned by Kuznar (1993), especially referred to species of Chenopodium proliferating in unusual concentrations in corrals. Herd animals transport these forage species to pastoral campsites where the plants thrive in the organic corral soils. This creates a mutually beneficial relationship where certain plant species become camp followers of pastoral campsites. This is the process by which plant invaders reach the status of weeds first and, later on, the status of cultivars, according to Vavilov (1938). And this process may explain the fact that the majority of the most aggressive and cosmopolitan weeds are edible. Initially, plant domestication began early, and in an unconscious way, probably in the Paleolithic Age, in primitive hunter-gatherer cultures (Rapoport et al. 1995). It is interesting to note that leaf-cutting ants (Acromyrmex), as determined by Farji-Brener (1996), show clear foraging preferences for exotic ruderal weeds which, according to Coley et al. (1985), are plants that invest more energy in reproduction, growth and dispersal than in anti-herbivore chemical defenses. It is suggestive that 52% of the early introductions (archaeophytes) in Poland listed by Trzcinska (1982) are edible.

Our results show that in anthropic habitats there are immense amounts of edible plants which are not always totally profited from. This is clearly evident in Argentina where people have almost lost the ancient practice of gathering wild food plants. In a tropical area such as Coatepec, the overall ‘standing crop’ averages 2.1 tons/ha whilst in temperate Bariloche it reaches 1.3 tons/ha. Tropical weeds are richer in species number and more productive than temperate weeds. The latter are almost absent during the long winter season, although they can be dehydrated and cooked during the cold season.

Because a significant sector of the Argentine population suffers from serious problems of malnutrition, the Universidad del Comahue and Municipalidad de Bariloche published a booklet (Rapoport et al. 1997) illustrating the 20 most common edible weeds. Free copies were distributed in provincial public schools. This instruction manual represents the beginning of a program which hopes to restore, at least partially, our ancestors’ knowledge. As a result of this printed information and a television program, a substantial increment of popular awareness and utilization of this resource, was registered.
 
 
Acknowledgements

Our thanks to Andrea Premoli, Tom Witham and Barbara Drausal for their useful comments on the article.
 
 Resumen

Las malezas abundan en ambientes urbanos y rurales. Según la región y lugar, hasta el 66% de las especies de malezas pueden ser comestibles y constituir un recurso alimentario adicional para el ser humano. Sobre la base de 400 muestras de ¼ m2 cada una, recolectadas en áreas tropicales (rutas, terrenos baldíos, calles y plantaciones en Coatepec, México) el promedio de la biomasa en peso fresco varió entre 1 277 y 3 582 kg/ha. Un muestreo similar en un área templada (739 muestras en Bariloche, Argentina) arrojó valores medios entre 287 y 2 939 kg/ha. En total se registraron 43 especies en Coatepec y 32 especies en Bariloche. La media general (total) fue de 2.1 y 1.3 ton/ha, respectivamente. A una escala geográfica mayor, una comparación entre las malezas mexicanas y argentinas no mostró mayores variaciones regionales en cuanto a qué partes u órganos son los comestibles. En ambos lugares, el orden de aprovechamiento, de mayor a menor, fue: hojas, semillas, raíces, frutos, infusiones, flores y condimentos. Las raíces comestibles (incluyendo bulbos y rizomas) parecen ser más comunes entre las especies perennes que entre las anuales.
 

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1. Instituto de Ecología, Ap. Postal 63, Xalapa 91000, Veracruz, México. martha @ecología. edu.mx
2. Universidad Nacional del Comahue, Departamento de Ecología, 8400 Bariloche, Argentina and CONICET rapoport@cab.cnea.edu.ar
3. The sequence of authors was alphabetically ordered

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