Calcium oxalate (CaOx) crystals in the tissues and organs of 18 species that belong to tribe Cardueae (Asteraceae), Arctium minus, Carduus candicans, C. nutans, C. pycnocephalus, Cirsium arvense, C. creticum, C. vulgare, Jurinea consanguinea, Silybum marianum, Tyrimnus leucographus, and Xeranthemum annuum within the subtribe Carduinae and Carthamus dentatus, C. lanatus, Centaurea cyanus, C. diffusa, C. iberica, C. salonitana, and C. solstitialis within the subtribe Centaureinae, were investigated, and their morphologies and distribution were determined using light microscopy. Two morphological types of crystals, styloids and prismatics, were the most commonly found crystals in the species examined. Raphides were only observed in the stem cortex and pith parenchyma cells of S. marianum, while druses were only viewed in the stem pith cells of C. pycnocephalus. Styloids were observed (if present) in the leaf, corolla, anther, filament, and style tissues. Prismatic crystals were common in almost all ovaries of the species investigated except Xeranthemum annuum which was found to include styloids in its ovary cells. Prismatics, styloids, raphides, and druses were present in the stems of the species. It is considered that crystal formation within the cell is under genetic control. Thus the type, and presence or absence of crystals may be represented as a taxonomic character. In conclusion, it is suggested that the type and location of CaOx crystals in the Cardueae constitute a diagnostic character and they may have taxonomic significance in this tribe. Keywords: Asteraceae, Cardueae, calcium oxalate crystals, prismatics, styloids Resumen: Se analizaron los cristales de oxalato de calcio (CaOx) en los tejidos y órganos de 18 especies que pertenecen a la tribu Cardueae (Asteraceae), Arctium minus, Carduus candicans, C. nutans, C. pycnocephalus, Cirsium arvense, C. creticum, C. vulgare, Jurinea consanguinea, Silybum marianum, Tyrimnus leucographus, y Xeranthemum annuum dentro de la subtribu Carduinae y Carthamus dentatus, C. lanatus, Centaurea cyanus, C. diffusa, C. iberica, C. salonitana, y C. solstitialis dentro de la subtribu Centaureinae. Se determinó su morfologías y distribución mediante microscopía de luz. Los tipos morfológicos de cristales más comúnmente encontrados en las especies examinadas fueron los estiloides y prismáticos. Los rafidios solamente se observaron en las células de la corteza del tallo y de la médula del parénquima de S. marianum, mientras que las drusas solamente se observaron en las células madre de médula de C. pycnocephalus. Los estiloides se observaron (si estaban presentes) en los tejidos de la hoja, la corola, anteras, filamentos, y el estilo. Los cristales prismáticos fueron comunes en los ovarios de casi todas las especies investigadas excepto en Xeranthemum annuum en donde se encontraron estiloides en las células de ovario. Los prismáticos, estiloides, rafidios y drusas estuvieron presentes en los tallos de todas las especies. Se considera que la formación de cristales dent...