The correct answer is option 2: genus. In taxonomy, the classification of organisms is based on a hierarchical system. The highest level in this system is the domain, followed by kingdom, phylum, class, order, family, genus, and species. Each level represents a different level of similarity and relatedness between organisms.

In the case of rose plants, all individuals belong to the same taxonomic category called the genus. A genus is a group of closely related species that share common characteristics and are more similar to each other than to species in other genera. For example, all rose plants belong to the genus Rosa.

Option 1: species, is incorrect because species is a lower level category within the hierarchy. Species represents a group of individuals that can reproduce to produce fertile offspring.

Option 3: family, is incorrect because family is a higher level category than genus. It represents a group of related genera.

Option 4: order, is incorrect because order is a higher level category than family. It represents a group of related families.

Therefore, the correct taxonomic category for all individuals of a particular organism, such as rose plants, is the genus.