Which flower features led botanists to view Magnoliales as primitive angiosperms?

Botanists historically regarded the Magnoliales as the most primitive extant angiosperm order due to several unspecialized structural features found in their flowers. These features include:12

• Floral Arrangement: Flowers typically possess numerous free parts arranged spirally on an elongated floral axis.13
• Stamens: Many members exhibit broad, leaflike stamens with pollen sacs embedded in their surfaces, rather than the distinct filaments and anthers seen in more modern groups.143
• Carpels: The female reproductive structures, or carpels, are often only slightly modified from a leaflike state. In many primitive species, these carpels are not fused and may be folded in a conduplicate manner.143
• Pollen: The pollen grains generally feature a single germination groove (monosulcate), a trait associated with early angiosperm evolution.14
• Perianth: There is often no clear differentiation into distinct sepals and petals; some primitive members lack a perianth entirely or possess a simple, undifferentiated one.4

While molecular evidence has since identified other groups as more basal, the order remains recognized as a foundational lineage among flowering plants.1