Introduction

Local knowledge worldwide about the use of plants is passed down from generation to generation, contributing to improve health aspects and well-being of low-income populations (^{Hurtado et al., 2006}). Each culture or civilization constructs an image of its surroundings, observes and feels differently goods and wealth that this provides and as a result, adopts a particular strategy of use and management (^{Toledo et al., 1995}). Since its appearance humans have been associated with plants, initially in its hunter-gatherer stage only as a consumer, since plants synthesize compounds and inorganic elements turning them into usable products (^{Hernández, 1971}); the relationship subsequently changes with the advent of agriculture. However, in recent decades, the Mexican tropics vegetation has been transformed as a result of changes in land use, being the most common the establishment of annual crops, the expansion of the agricultural frontier, and livestock and growth of urban areas, with inappropriate use of natural resources (^{Zamora et al., 2008}).

From the scientific point of view, this problem can be addressed through the use value index used to quantify the importance that plants have for local people (^{Prance et al., 1987}; ^{Phillips and Gentry, 1993}). Use values are based on the degree of consistency of repeated interviews with one or more informants (^{Pardo and Gómez, 2003}).

^{Flores and Albizu (2005)} worked with the characterization of plants use in the buffer zone of the Indio Maiz Biological Reserve in Nicaragua, where they reported plant species used for construction, food and medicine; Uvs values (use value index) were relatively high. ^{Hurtado and Moraes (2010)} conducted a comparison of plants use in two peasant communities from the Tucumano forest in Bolivia, the most commonly used species showed higher use value in both communities. In Tabasco, ^{Magaña (2009)} reported Uvs values between 2 and 7 for species only used as medicine.

Based on the above, the aim here was to evaluate the use value of plants species from the Ejido Sinaloa 1^st Section municipality of Cárdenas, Tabasco, under the hypothesis that species having higher use value in the locality correspond to medicinal plants.

Material and methods

Fieldwork was conducted in Ejido Sinaloa, first section, located in the municipality of Cárdenas Tabasco. It is a rural village (^{INEGI, 2005}) which is geographically located in the coordinates 18º 20' 22'' North latitude and 93º 44' 05'' west longitude. It is located in the coastal zone of the Gulf of Mexico (^{Bueno et al., 2005}), has a propensity to flooding due to increases in sea level that determine fundamental changes in its form and origin, as well as their physical -geographical landscapes and natural environment, it has a length of 2 775 km (^{Hernández et al., 2008}) and presents environments such as beaches, deltas, estuaries, tidal flats, dunes and coastal lagoons (^{Ortíz and Méndez, 1999}). The research was conducted in February 2009 to June 2010. The selection of the study area was delimited from field trips of maps and fieldwork locating places where plant species are concentrated, taking into consideration that this is an area away from urban centers; finding also that its inhabitants have diversified and enriched their home orchard.

The rural community is comprised by 113 households, and reports scarce technological influence, reason why it was chosen as a study area. The sample size n was determined following the methodology from ^{Segura and Honhold (2000)}, considering 3% maximum permissible error, which gave a value of n= 73 families with a probability of 95%. The methodology used corresponded to the ethnographic method proposed by ^{Pineda (1987)}, which consists in observing the daily life of the community, actively participating in social and cultural events of the population, in order to know the aspects related to the identification use and assessment of the flora, creating personal ties and work with residents. In the selected households, a first open interview was performed, in which the householders were asked for personal data (occupation, age, education, services at their disposal).

To obtain the use values the methodology from ^{Phillips and Gentry (1993)} was used, who mentioned that it is necessary to conduct two or more events (interviews) in a given period of time. In this case, two events were held. In the first interview with the 73 households were considered. A floristic list of species present in them was made. For the second event, the non-probability sampling known as "Snowball" (^{Goodman, 1961}) was used to select key informants, which consist in selecting an initial sample of people and through their information locate in others population people to be interviewed, activity that continues, till reaching the final stage corresponding to the moment when there are no people who are recognized by the locals.

The second part of the interview was semi-structured. Requesting information on known or plants grown in their fields, those using, what they use it for and frequency of use. The third phase included the quantitative determination of cultural importance or level of use that people give to plants. To calculate the use value of each species (Uvs), before must calculate the value use index (Uvis) of each species per informant, using the following formula:

Where: Uis is the number of uses mentioned for the species s by the informant i; n_is= the number of events in which the informant i mentioned a use for the species s; Subsequently Uvs was determined calculated with the following formula:

Where: ni is the total number of informants interviewed for the species s, i.e. the sum of the use value of informants for a species, divided by the total number of informants (^{Phillips, 1996}).

Results and discussion

91 useful plant species were recorded in the study area, which are grouped in 51 botanical families, the best represented families were Fabaceae with tamarind (Tamarindus indica L.), flamboyant (Delonix regia (Bojer.) Raf., quickstick (Gliricidia sepium (Jacq.) Steud), emperor’s candlestick (Senna alata L.), chipilin (Crotolaria longirostrata Hook. et Arn.), beans (Phaseolus vulgaris L.) and gray nicher (Caesalpinia bonduc (L.) Roxb), Rutaceae with species such as lemon (Citrus lemon (L.) Burm), orange (Citrus sinensis L.), sour orange (Citrus aurantium L.), mandarin (Citrus nobilis Andr.), orange jessamine (Murraya paniculata (L.) Jacq.), and rue (Ruta graveolens L.).

Lamiaceae with species such as basil (Ocimum basilicum L.), peppermint (Mentha piperita L.), pennyroyal (Mentha pulegium L.), coleu (Coleus sp.), Chinese chastetree (Vitex aff. negundo L.) and lemon balm (Melissa officinalis L.); within the Euphorbiaceae recorded cassava (Manihot esculenta Crantz.), Mayorga (Pedilanthus tithymaloides Poit.), Chaya (Cnidoscolus chayamansa Mc. Vaughn.) and fig tree (Ricinus communis L.). Of selected key informants, the data indicate that men cited nine species, while women only three. Table 1 shows that respondents between 41 and 60 years old recognize a greater number of species (eight species men and 11 women) and are the people who have more knowledge about species and their uses.

Table 1 Species mentioned by respondents according to gender and age ranges. 

NEM= número de especies mencionadas.

The above results are consistent with ^{Magaña et al. (2010)}, who report increased knowledge of plants by men in Maya-Chontal communities from, in turn differs from that reported by ^{Hernández et al. (2005)}, who in his research made in Puebla is where women are those that identify a greater number of species, especially medicinal. Elderly key informants acknowledge more species. This is related to the fact that population consists mostly of men and they are the ones who collect the largest number of species, as in their work area plants are always present.

Use value

14 species were found with values between 1.0 and 3.85 (Table 2). The species with the highest use value are those from which the same part of the plant is used to meet various needs. The species that presented higher use value was the coconut (Cocos nucifera L.) mentioned by 10 respondents, the fruit of this plant is of great importance in the coastal areas of Mexico as it is a source of income (^{Moscoso et al., 2002}); followed by lemon (Citrus lemon (L.) Burm.) and coleu (Coleus sp.). Lower values (≥0.5) correspond to twenty species among which are agave (Agave angustifolia Haw.), Sweet potato (Ipomoea batatas L.) and chipilín (Crotolaria longirostrata Hook. Et Arn.) and those that have a very specific use, as food or firewood.

Table 2 Use value of species recorded in the ejido Sinaloa 1^st section, Cardenas, Tabasco. 

There are species that have high Uvs like red mombin (Spondias purpurea L.) and lemon (Citrus lemon (L.) Burm.), both used for medicine and food. On the contrary species with low Uvs values like custard apple (Annona reticulata L.) and genipapo (Genipa americana L.) report one specific use as food.

Not all plants have the same importance of use, many of which may have low Uvs values compared with other species, possibly due to poor knowledge about other potential uses (^{Martin, 1995}). This is confirmed by ^{Toscano (2006)}, who reports that using the use value index is biased if it is approach from the perspective that a species can increase its value if it is used in other ways. Most of the recorded species have multiple uses, so a medicinal species can also be used for food or ornamental. Therefore, Uvs values vary from one species to another depending on the importance that each social group provides to its plant species.

Sometimes knowledge varies from person to person, some people use a species for a particular purpose and others give them different uses, in many cases, the uses are unknown. The knowledge that a person may have is different from another, for example, a person can use it to cure or prevent any disease and another for food or ornamental. This coincides with ^{Garro (1986)}, indicating that the knowledge that a human being can have is determined by its role in society and their characteristics: gender, age and work, among others.

The reported number of useful species was relatively low compared to other localities like Tapotzingo, Tecoluta and Mazateupa in Nacajuca, Tabasco (^{Magaña et al., 2010}) and in the swamps of Centla and Boca del Cerro, Tenosique, Tabasco (^{Sol et al., 2000}; ^{Sol et al., 2006}). This is due largely that in some locations spanning the coastal zone, including the ejido Sinaloa 1^st section, through the years the sea has invaded territorial spaces, causing loss of habitable spaces, land destruction, erosion and flooding lowlands, preventing the growth of plants and causing the disappearance of plant species (^{Hernández et al., 2008}).

Regarding botanical families the highest Uvs percentage (8.01%), corresponded to the Rutaceae, followed by Arecaceae (7.53), Combretaceae (4.48%) and Fabaceae (4.29%). Only two species of Arecaceae were recorded, but both had a high use value compared to other families like Fabaceae or Combretaceae. The high value that Rutaceae family had was because its species are used for different purposes. A family can have several species but the percentage will be lower if the species that comprise it have low Uvs.

The species that showed high use value have different purposes and few plants were used as shade and ornamental. Otherwise, the species with low use value are those that have a specific use such as those for magic-religious ritual or those which are used as smoke and flavorings. The best botanical families represented in the useful flora from the ejido were Rutaceae, Fabaceae, Euphorbiaceae and Lamiaceae; half of them coincide with those reported by ^{Burgos (2009)} for Atzalan, Veracruz, who recorded families such as Rubiaceae, Fabaceae, Euphorbiaceae between the 10 best represented.

In the study area, of the listed plants, most are used as medicine and were the most important regarding the number of species used for this purpose. This may indicate that the community has greater specificity for the use of its resources and also have a better understanding of healing properties of plants. In this regard, ^{Galeano (2000)} mentions that in all studies there are some species with relatively high use value, but are represented by few individuals, mainly wood and palm species, so it is considered that such high use value correspond more than one exceptional feature than a group of species. ^{Maldonado and Ramírez (2008)}, in Loja, Ecuador and ^{Magaña (2009)}, in Tabasco, Mexico acknowledged Uvs values ranging from 1-8 and 1-7, respectively; those found in this study are generally lower as these range from 0.05 to 3.8, which is mainly attributed to the forests have great plant species diversity and, therefore, the given uses are multiple.

Another important factor is that the areas that are furthest from urban areas are increasingly turning to the use of plants that are located in the locality. In addition, in this case, to salinity, favored by strong pollution from the opening of Boca de Panteones, causing wilting and death of plants, mainly medicinal that are planted in backyards and that most are introduced, (^{Hernández et al., 2008}). An important aspect is that the inhabitants of the ejido Sinaloa resort increasingly less to the use of medicinal plants, which has led to the tradition of healing and prevent disease with these plants is being lost, which contrasts with the Maya-Chontales communities reported by Magaña, where people prefer to resort to the use of plants to cure and prevent disease, avoiding the loss of traditional knowledge.

High Uvs values correspond to species used as medicine. These data don’t agree to that reported in Colombia by ^{Marin et al. (2005)} who states that species with lower use value are medicinal, food and some for construction mainly, and contrasts with those reported by ^{Phillips and Gentry (1993)} in Peru and ^{Galeano (2000)} in Colombia, who found that the most commonly used species are timber, although in this case, respondents did not report any species for exclusive use as timber. Plant species used for medicine and food are similar to those reported by ^{Bermúdez and Velázquez (2002)} in Trujillo, Venezuela and ^{Toscano (2006)} in Colombia, specifically, bitter melon (Momordica charantia L.) and pomegranate (Punica granatum L .), whose Uvs values are similar and are used in the treatment of diabetes in the first case and in the second fresh consumed.

Conclusions

In the study are there is broad cultural knowledge of plant species in the area. Local knowledge accumulated on the species, proved to be related based on gender, as men over 61 years, mentioned more species and greater use. Furthermore, the use of species is determined by the knowledge possessed by each inhabitant on the species and purpose of their use. The greatest use value was recorded in Cocos nucifera L., which reported medicinal, food, firewood, smoke (repellent) and construction uses.

The family with the greatest number of species was Fabaceae, with species such as Crotolaria longirostrata Hook. et Arn., Gliricidia sepium (Jacq.) Steud, Delonix regia (Boj), among others. Most respondents prefer to sow plant species in their home orchards to be able to give them the necessary care and facilitate their consumption. It is possible to recall the traditional knowledge about the use of the species, especially those that over time have been lost and are essential as medicines and food.