The Cultural significance (CS) of an organism has been defined as the importance of the role that the organism plays within a particular culture . It has been used in ethnobotanical research in lexical retention [2,3]; to predict changes in the content of folk biological classifications, to asses the significance of a class of resource on the basis of its nomenclatural elaboration ; historical and archeological studies of human ecology and subsistence strategies [4-6]; perceptual salience of organisms ; and the borrowing of folk names, products and information about plants between cultures .
In earlier research, the CS of plant resources was estimated by simple scales of significance subjectively assigned by the researcher [c.f. [2,3,9]], but as Turner  points out these scales "are too simplistic to account for all the variables involved and not rigorous enough to be used with minimal bias". Furthermore these scales are restricted to the nature of the culture that is being studied, are established by the objectives of the researcher and do not allow cross-cultural analysis . Hunn suggests that plant CS (practical significance in his terms) first must be described in sufficient detail to discriminate taxa from each other, and only then it can be measured. He also proposes that this description, known as activity signature, must be done from an intracultural or native perspective [ex. ].
Turner  developed the first theoretical model of CS. Her principal assumptions were that: CS is equal to use, when "use" is interpreted in its most general context, which means that knowing something is using it; every recognized plant have some degree of CS; and, CS vary in quality, intensity and exclusivity. The product of these three variables determines the "use value" of each use. Thus, her Index of Cultural Significance (ICS) of a plant is the sum of its "use values". However, these data are subjectively determined by the researcher  and not by informants in independent interviews. This model was modified by Stoffle et al. [12,13] based on the same assumptions, but adding the parts of a plant used for each purpose in the 'quality of use' category, and the 'contemporary use' variable category into the formula. More recently  also modified the Turner's model; they limited the answers categories for each variable to a binary system to make responses more objective; and they added a correction factor to the formula that modifies every use value with a measure of informant consensus. All previous techniques are concerned with measuring the CS so they include few variables where the importance of a resource is reflected, instead of using a mayor number of variables determining the CS.
Phillips and Gentry  proposed another way to measure the relative usefulness of plants, and refer to it as 'use value'. This was explicitly designed to allow hypothesis testing based on interviewing techniques, nature of data and statistics. The use value of a plant for an informant (UVis) is the average of the number of different uses assigned to that plant in several different interviews. The overall use value of a plant (UVs) is the average of the UVis of each informant. Phillips  classified this technique as part of the "informant consensus" methods that allows quantitative analysis of informants' knowledge. This approach, first proposed by Trotter and Logan  and Romney et al. , measures the relative importance of uses or species directly from the degree of consensus in the answers of informants in independent interviews . Although informant consensus is efficiently used in ethno-pharmacological prospective surveys [16,18-20], it does not permit a thorough examination of the complex phenomenon of CS .
Pieroni  applied a compound index to edible plants, the Cultural Food Significance Index (CFSI). His index differs from earlier proposals because it is the first explicitly developed for food resources, and because it includes a more detailed group of factors influencing CS that will be treated in detail in methods.
Almost all efforts to evaluate the CS of resources have been focused on plants. Pieroni  was the first including in his dataset some (8) mushroom species, but his index does not take into account the particularities of mushrooms and the knowledge around them. Montoya et al.  used the frequency of mention from a free listing as an indicator of CS of mushrooms. By correlating these frequencies with the abundance and price of mushrooms, she found that the frequency of mention has a low but positive correlation with prices and a medium negative correlation with abundance. Although these two variables might be influencing the CS of mushrooms she proposed for further studies to take into account more variables (knowledge of habitats, fruiting season, morphology, recipes and eating preferences) to assess more precisely the cultural value of mushrooms.
To recap, the study of CS of resources is a keystone in the development of an analytical and quantitative ethnobiology. It has many applications, but its successful use depends on the quality and accuracy of its measurements. That is why we have to understand it first and then measure it . Through time, research has tended to give more detailed and complete descriptions of CS (Figure 1). However, compound indexes have to be thought of on the one hand, as tools to separate, analyze and understand the CS phenomena; and on the other, as techniques to estimate it.
In this paper, using the traditional mycological knowledge of Zapotecs from Oaxaca, as a model, we evaluate and analyze the CS of wild edible resources by a compound index. We measure the CS of edible mushrooms in function of their total score in a compound index; and undertake an inductive analysis of the reasons that determine the CS of edible mushrooms.