Achene micro-macromorphological characteristics of Centaurea L. Section Mesocentron (Cass.) DC. (Asteraceae) in Türkiye and their taxonomic importance

Achene morphology of section Mesocentron was examined in detail with scanning electron microscopy (SEM) and stereo microscopy (STE). A total of 24 characters were utilized, comprising 19 for achenes and five for the pappus. Achene length ranges from 1.853 to 4.191 mm, achene width from 0.888 to 1.636 mm, achene perimeter from 5.283 to 10.434 mm, and achene surface area from 1.465 to 4.626 mm 2 . Achene color is dark brown or light brown; indumentum is glabrous or pubescent; ornamentation is undulate, smooth, or imbricate; boundaries are straight, thin, slightly raised or grooved, and centers are irregularly raised, almost flat, or slightly grooved. Pappus length ranges from 2.249 to 4.507 mm, its type is barbellate, and its color is whitish or straw. Achene color, indumentum, length, perimeter, surface area, ornamentation, and pappus length contribute to the differentiation of taxa, while achene and cell shapes (obovoid and elongated) and pappus type (barbellate) did not make a difference. This study marks the first examination of achene surface area and perimeter within the genus Centaurea . Moreover, ’imbricate’ surface ornamentation on achenes has been documented for the first time in any Centaurea species. Three of the four taxa analyzed have undergone micromorphological analysis for the first time.