The aim of this study included the phytochemical screening of extracts and essential oil of Erodium cicutarium (L.) LâHér. ex Aiton (Geraniaceae), a native traditional medicinal plant from Croatia, as well as a highly detailed micromorphological characterization of its aerial parts. The contents of total polyphenols and tannins (TP and T), total flavonoids (TF), and total hydroxycinnamic derivatives (THD) in plant extracts were quantified in plant material from 4 localities (Plitvice, Podvinje, Buzin, and Trešnjevka). The contents of TP, T, TF, and THD significantly varied depending on the collection site, and were in the range of 4.78%-12.85% (TP), 3.23%-5.80% (T), 0.42%-1.09% (TF), and 1.08%-2.59% (THD) of dry weight of plant material, with the Plitvice collection having the highest polyphenol content. GC-MS analysis of the essential oils showed a similarity in composition of the major compounds from all investigated populations. Fifty compounds were identified in all 4 investigated oils (90.4%-96.7% of total oil) and classified into 7 structural classes, with hydrocarbons (59.8%-65.7%) as the main class of constituents. Two types of trichomes, nonglandular and glandular, were observed on the calyces, leaves, and stems, including 3 capitate trichome types. The bioactive substances and micromorphological characterization of Croatian populations of E. cicutarium were investigated for the first time. In general, the scanning electron microscopy imaging of Erodium cicitarium trichomes has not been reported before.