The structure of folk taxonomies of living organisms has been a major focus of the cognitive ethnobotanical literature of the last several decades. A key part of the discussion has been a debate over the relative importance of morphological, ecological and utilitarian factors as bases for folk taxonomies 1234. Despite extensive treatment of this subject, the literature still contains surprisingly few detailed descriptions of the specific sensory criteria used for judging membership in taxonomic categories. Some authors 25 have included sets of contrasting features for folk species within polytypic folk genera. However, the importance of chemosensory criteria (taste and smell) for folk classification and identification has been addressed very little.

The question of how people distinguish plants with particular kinds of medicinal activities from the many species growing in their local environment is one of great interest to the fields of ethnopharmacology and medical ethnobotany 6789. Odor and taste, along with visual and tactile clues tend to be important means for recognizing medicinal plants cross-culturally. In some cases, sensory clues are related to beliefs about illness etiologies. Glenn Shepard 9 reports that the Matsigenka and Yora ethnic groups of the southern Peruvian Amazon believe that foul smelling atmospheric vapors and spirits can cause sickness among people. The Matsigenka use strong smelling aromatic plants to combat these harmful influences. In contrast, the Yora say that the spirits of strong smelling plants can cause illness, and, following a homeopathic logic, are also capable of curing the same illnesses that they cause. Lisa Gollin 6 has investigated the sensory clues that allow the Kenyah Leppo' Ke of Borneo to recognize medicinal plants. Her research particularly focuses on the association of particular kinds of tastes and odor qualities with particular kinds of healing properties. Gollin points out the importance of volatile and essential oils for the medicinal properties of plants. Similarly, Leonti et al. 7 report the kinds of odors and, particularly, tastes, that are associated with healing plants among the Popoluca of southern Veracruz, Mexico. Pieroni and Torry 8 have recently compared tastes associated with medicinal activity among Gujarati, Kashmiri and English informants.

Shepard 9 has argued for the need to explore cross-cultural sensory experience from a multidisciplinary perspective. He notes that accounts of sensation from anthropology have often ignored the contributions of the biological sciences. Shepard proposes "sensory ecology" as a new theoretical framework for a cross-cultural understanding of sensation. Sensory ecology would seek to draw both from the scientific understanding of the physiology of sensation and the cultural factors that lead interpretations of sensation to vary within those physiological constraints. Shepard writes "... [S]ensory ecology would be equally interested in cross-cultural variation and similarities and should incorporate physiological understandings and cultural constructions of sensory perceptions within a broad biocultural model addressing human-environment interactions" [9, p.264].

This paper seeks to clarify the importance of the chemosensory clues odor and taste to classification and identification of trees among the Aguaruna Jívaro of the Peruvian Amazon. It will focus specifically on the Aguaruna folk life-form númi (tree excluding palms). Bark smelling plays a particularly important role in tree identification among the Aguaruna, since features such as leaves, flowers and fruit can be difficult to examine closely, particularly for large canopy trees (Figure 1). Taste plays a more limited role in identification of woody flora but is still a salient feature of some trees, particularly those with edible fruit. The data that form the basis of this paper were collected during the author's dissertation research 10, which examined sensory and ecological clues that influence the Aguaruna Jívaro of the Peruvian Amazon in their classification and identification of local tree species. A more general treatment of those research results has already been published elsewhere 11. This article will focus more narrowly on the role that the chemosensory clues taste and, particularly, odor, have for Aguaruna ethnobotany.

In the Aguaruna language, the distinction between smell and taste is not as clear cut as in English. The verb kugkúut means 'to smell', 'to taste' and also 'to kiss' 12. Just like the verbs 'to smell' and 'to taste' in English, kugkúut is used to describe both the production of an odor or taste and the perception of an odor or taste. For example, if an Aguaruna collaborator were to pick a leaf from the shrub untuntúp (various Piper species, Piperaceae) and hold it out for me to smell he might say "Yatsuj

ú

The odors of some trees contribute directly to their usefulness. The Aguaruna wear the seeds of chikáunia (Myroxylon balsamum, Fabaceae) and the fruit of batút (Ocotea spp., Lauraceae) on necklaces because of their pleasant fragrance. Only women wear chikáunia. When I asked male Aguaruna informants to describe the odor of this species, they would often answer "Chikáunia n

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The Aguaruna verb dekapét means 'to taste', 'to try' and 'to test' [12, p.37]. The taste of the fruit, bark or sap are salient characters for some trees. Aguaruna taste terms, include the following: yumímitu – 'sweet', yapáu – 'bitter', kajiáu – 'fermented' chujuín – 'sour', tsupáu – 'acrid', tajáu – 'spicy and sákam – 'tasteless'. By far the most common taste term used to describe trees is yumímitu – 'sweet', for edible fruits of many species. Except for sákam, these terms are specific to taste and are never used to describe odors. This fact supports the idea that odor and taste are cognitively separate domains, despite the existence of the verb kugkúut, which encompasses both meanings. Common Aguaruna taste and odor terms are given in Table 1.

For the Aguaruna, many tree odors are idiosyncratic. In other words, people often cannot describe the smells of the bark, sap, fruit or flowers except in terms the tree itself, or other related trees. For example, the likely response to the question: Yatsujú, chikáuniash wají wají kugkwáwai? – 'Brother what does chikáunia (Myroxylon balsamum, Fabaceae) smell like?' would be simply: Yatsujú, chikáunia chikáunia kugkúawai – 'Brother, it smells like chikáunia.' Clearly, the lack of abstract smell terms creates a problem for cross-cultural understanding. The only way to adequately communicate what chikáunia smells like to a person who has never smelled it before would be either to cut a piece of bark as an example, or, perhaps, assuming technological feasibility, to extract the essential oils and make a scratch and sniff sticker 10.

Only in a few cases, were informants able to describe the odor of a tree in non-botanical terms. When I asked one informant about the odor of the bark of shishím (Couroupita subsessilis, Lecythidaceae), he replied 'Íki íki mejéawai' – 'It smells like farts.' Another informant said that the heartwood of the tree ugkuyá (Tachigali formicarum, Fabaceae) smells like púku – 'pus.' Also, for many informants, the default smell of trees that do not have any other distinctive odor is: 'séj' – 'blood.' However, other people say of trees with no strong odor simply: 'Númi númi mejéawai' – 'It smells like a tree.'

Of the 182 tree folk genera recorded in this study, 51 (28%) were widely considered to possess a distinctive odor (see Table 2 in Additional file 1). Informants often said that trees that they considered to be related as companions have similar odors. Thirty-nine of the 51 trees listed in Table 2 (see additional file 1) (76%) have odors that are considered to be similar to some other tree. For example, most people said that the fruits and bark of the trees takák (Ocotea gracilis, Lauraceae) and máegnum (Ocotea floribunda, Lauraceae) have a very similar smell. Takák and máegnum are also considered to be companions along with other Lauraceae found in the area. Trees that the Aguaruna consider to have similar odors are almost always in the same botanical family. However, people occasionally compared odors across the Burseraceae and the Meliaceae.

Informants often recognized subtle distinctions among trees they consider to have similar odors. The most important feature uniting members of the Lauraceae in group 4 (see Table 2 in Additional file 1) is the distinctive aromatic odor of the bark and fruit. Gentry also notes that many Lauraceae have a characteristic leaf or bark odor due to the presence of essential oi ls [16, p.40]. Batút (Ocotea spp., Lauraceae) has an odor that is similar to the other members of its group, but is more rank. Káikua (Licaria sp., Lauraceae) has a particularly rich perfume-like smell.

Aguaruna informants very rarely compared the odors of trees they did not consider to be related. Members of the genus Protium and the genus Dacryodes (both in the Burseraceae) tend to have a strong odor in the trunk and twig bark, sap and fruit 16. I find the odor to be similar to frankincense, copal, and also reminiscent of freshly cut dill. The Aguaruna consider members of these two genera to have similar odors, but they do not group them together as companions. One reason most informants separate Protium and Dacryodes is that the characteristic fruit of each is quite distinct. Protium has fruit that dehisce to reveal a soft white aril [16, p.302] surrounding a single hard seed. Dacryodes, however, has indehiscent fruit.

Table 2 (in Additional file 1) contains 12 trees out of 51 (24%) whose odors informants considered to be unique. Trees with very distinctive odors were almost always also said to be unrelated to any other trees as companions. A few informants placed tsáik (Cedrelinga cateniformis, Fabaceae) with séetug (Cedrela odorata, Meliaceae) and awán, which refers to Cedrela odorata, or Swietenia macrophylla (Meliaceae) 17, because all are important timber trees. Likewise, informants occasionally put the trees chíajap (various Trichilia, Meliaceae), ishpíg (Guarea macrophylla spp. macrophylla, Meliaceae) and tapákea (Guarea kunthiana, Meliaceae) with other trees in the Meliaceae or even the Burseraceae. However, none of the above groupings were recognized by a majority of informants.

Some trees have fairly subtle odors. For example, Aguaruna informants typically said that the tree magkuák (Cespedesia spathulata, Ochnaceae) "imáchik magkuák magkuák kugkúawai" - 'smells a little bit like magkuák.' Other trees (see Table 2 in Additional File 1) with odors that are distinctive but weak include kántsa (various Euphorbiaceae), dátash (Aparisthmium cordatum, Euphorbiaceae), káashnum (Eschweilera gigantea, Lecythidaceae), shuwát (Eschweilera sp., Lecythidaceae), chinchák (various Melastomataceae), ipák (Bixa orellana, Bixaceae), tsáik (Cedrelinga cateniformis, Fabaceae) and tsáchij (Senefeldera inclinata, Euphorbiaceae). Some informants do not even recognize that the above species have distinctive odors. Interestingly, Gentry 16 also does not mention odor as a clue for recognizing the above taxa.

As mentioned previously, by far the most common taste term that Aguaruna informants used to describe trees is yumímitu – 'sweet.' I found that this term is commonly applied to just about any fruit that is edible, including ones such as apái (Grias peruviana, Lecythidaceae) that I did not find to be particularly sweet. Of the 182 folk genera collected in this study, 39 (21%) have edible fruit. Informants mentioned taste very rarely for cases other than edible species. One person described the bark of wámpa (Inga edulis, Fabaceae) as yumímitu – 'sweet.' Some informants described the bark of the trees yapúkuit (Ferdinandusa sp., Rubiaceae) and bíchau (various Meliaceae) as yapáu – 'bitter.' The sap of tsémpu (various Myristicaceae) and the fruit of yantsáu (various Guarea, Meliaceae) were also said to be bitter. Fruit of some trees, such as the cultivated toronja (Citrus sp., Rutaceae) are described as chujuín – 'sour.' The sap of ujúshnum (Croton lechleri, Euphorbiaceae) is tsupáu – 'acrid.' I did not encounter any instances of tajáu – 'spicy' in descriptions of trees, but it does apply quite well for the roots of ajég (Zingiber officinale, Zingiberaceae) and ampágpag (some Piper species, Piperaceae). Kajiáu – 'fermented' did not appear in any tree descriptions.