This system of classification was used by Linnaeus

The correct option is Artificial system.

Carolus Linnaeus used the artificial system of classification for grouping organisms, particularly plants.
This system is based on one or a few superficial, easily observable morphological characters rather than overall natural relationships.

In his botanical work, Linnaeus classified plants based primarily on sexual characteristics, specifically the number and arrangement of stamens (the androecium structure). Because this system relied on a very limited number of features, it grouped together many unrelated plants while separating closely related ones, which is a key characteristic of an artificial classification system.

To understand why the other choices are incorrect:
1. Natural system: This system is based on natural affinities and considers multiple characters including anatomy, embryology, and phytochemistry (such as the system proposed by Bentham and Hooker).
2. Phylogenetic system: This system classifies organisms based on their evolutionary relationships and common ancestry.
3. Asexual system: This is not a recognized system of biological classification.