Which condition is characterized by abnormal gingivae?

The condition characterized by abnormal gingivae is epulis. Epulis refers to a variety of lesions that can arise on the gingiva or alveolar mucosa, leading to changes in the appearance and structure of the gums. These lesions may present as swellings or growths that can be either benign or more concerning, depending on their specific type. The inflammation or proliferation of tissue in epulis can manifest as abnormal gingival tissue, which differentiates it clearly from other options in the question.

Canker sores, while they may cause discomfort in the oral cavity, do not alter the gingival structure in the way that epulis does. Oral melanoma primarily affects the mucosal tissues but is notorious for its characteristics such as pigmentation changes rather than typical alterations of the gingiva alone. Thrush, or oral candidiasis, affects the mucosal surfaces and may lead to white patches but does not directly indicate abnormality of the gingivae as a primary feature. Thus, the unique association of epulis with abnormal gingival changes confirms it as the correct answer.