Knowledge of medicinal plants has accumulated over centuries and often represents the only
therapeutic resource of small municipalities in the interior of Brazil. The objective of this study was to
evaluate the knowledge and use of medicinal plants by the population of the municipality of Bom
Princípio do Piauí, Piauí state, for the treatment of diseases in humans and domestic animals.
Interviews were conducted with 38 residents using standardized questionnaire forms, with the
"snowball" technique. Fifty nine families, 98 genera and 112 species were recorded. Of these, 22.3%
were indicated for the treatment of diseases in animals and 9.8% were said to cause adverse effects.
The families with most species were Fabaceae (14), Euphorbiaceae (11) and Lamiaceae (6). The species
with greatest use value (UV) were Myracrodruon urundeuva Allemão (0.65), Dysphania ambrosioides
(L.) Mosyakin and Clemants (0.63) and Amburana cearensis (Allemão) A.C.Sm. (0.42). The leaves were
the parts most frequently used (26.8%), followed by bark (21.0%). Of the 15 used categories listed in this
study, those with the highest number of recorded species were related to illnesses associated with the
digestive tract (102), diseases of the genitourinary system (72) and diseases of the respiratory system
(60). This study revealed the importance of knowledge and use of medicinal plants in caring for the
health of people and domestic animals in the municipality. In addition, the study provided information
on plants of the local flora with pharmacological potential.