<p>Plant galls are newly formed structures that develop due to the influence of gall-inducing organisms, providing them with shelter, protection, and nourishment. The most commonly studied galls are caused by insects. Plant-parasitic nematodes (PPNs) induce gall formation in various parts of plants, primarily targeting the roots. Reports on their effects on aerial parts, especially flowers, are rare. In this study, floral galls induced by <i>Ditylenchus</i> sp. (Anguinidae) in <i>Bongardia chrysogonum</i> (L.) Spach (Berberidaceae) were introduced for first time. The structural traits of galls were analyzed using microscopic studies. The levels of total phenolic compounds and anthocyanins were measured by spectrophotometric methods. Intact flowers had thin sepals and petals with 3–5 cell layers, tetrasporangiate anthers, and a thin pleated gynoecium, while the galled floral parts lacked morphological and anatomical similarity to the intact organs. These galling organisms triggered the regeneration and reorganization of floral parts, leading to abnormal and swollen growths. The number of modified floral whorls in produced gall ranged from 1 to 3, indicating that nematode infection affected some or all floral organs. Microscopic sections of all galls showed homogeneous parenchyma with large intercellular spaces, lacking a gall chamber, and containing numerous nematodes within the tissue. Galled flowers showed red–purple coloration and higher phenolic compound concentrations than normal flowers, as revealed by cytochemical and biochemical analyses. The reorganization of floral parts and the large intercellular spaces can be used for nematode survival and dispersal. High levels of phenolic compounds suggested host plant defense against the nematode.</p>