The correct answer is Fissured tongue.

- Fissured tongue is considered a benign anatomical variation rather than a pathological condition.
- It is characterized by the presence of multiple grooves or fissures on the dorsal surface of the tongue.
- These fissures vary in depth and length and usually do not cause any symptoms or require treatment.
- The exact cause is unknown, but it is often seen as a normal variation in the general population and may be associated with aging or certain syndromes like Melkersson-Rosenthal syndrome.

In contrast, the other options represent conditions that may have underlying causes and could require clinical attention:

- Median rhomboid glossitis: This is a chronic inflammatory condition often associated with candida infection, presenting as a smooth, erythematous, rhomboid-shaped area in the midline of the dorsal tongue.
- Geographic tongue: Also known as benign migratory glossitis, this condition manifests as areas of depapillation with irregular, map-like patterns that change location over time. It is benign but can sometimes cause discomfort or sensitivity.
- Black hairy tongue: This condition results from the elongation and hypertrophy of the filiform papillae on the tongue surface and is associated with factors such as poor oral hygiene, tobacco use, or antibiotic therapy. It is reversible but may require treatment.

Reference: Oral Pathology for the Dental Hygienist, Volume 1, Chapter 5, Page 130