What description fits a margin that is smooth?

The description that fits a margin that is smooth is "entire." When referring to the margins of a colony of bacteria or fungi, "entire" indicates that the edge is smooth and without any irregularities, not exhibiting any projections or indentations. This characteristic gives it a clean, even appearance.

In contrast, “undulate” refers to margins that have wave-like projections, while “lobate” describes a margin that has large, distinct lobes or rounded projections. “Filamentous” indicates a fringe-like, hair-like border, creating a more complex appearance. Understanding these terms helps in accurately describing the morphology of microbial colonies, which can be essential in identification and study in microbiology.