Why were Fagales once grouped with unrelated plants in Amentiferae?

The classification of Fagales within the artificial group Amentiferae was based on shared morphological characteristics rather than evolutionary relationships.

Botanists historically grouped these plants together because they all possess catkins, also known as aments. The primary features defining the Amentiferae included:

• Staminate (and often pistillate) flowers arranged in catkins.1
• Reduced or entirely absent sepals and petals.1
• A shared evolutionary trend toward wind pollination, or anemophily.1

Because these traits were viewed as a unified set of characteristics, unrelated families were erroneously placed in the same category. Modern classification systems, such as the Angiosperm Phylogeny Group (APG), have since corrected this by placing Fagales within the Rosid I group among the core angiosperms, reflecting their true genetic and evolutionary lineage rather than superficial similarities in reproductive structures.1