Why did scientists once think gnetophytes were closely related to flowering plants?

Scientists once hypothesized that gnetophytes were closely related to flowering plants (angiosperms) due to several shared morphological and anatomical characteristics that appeared to bridge the gap between gymnosperms and flowering plants.1

Key reasons for this historical classification included:

• Vessel elements: Gnetophytes possess vessels in their xylem (wood), a feature typical of angiosperms but generally absent in other gymnosperms.1
• Strobili structure: The compound nature of their pollen-producing and seed-producing strobili led some botanists to interpret these structures as "inflorescences" or flowers.1
• Double fertilization: The presence of a unique system of double fertilization in gnetophytes suggested a potential evolutionary link to the double fertilization process found in flowering plants.2

However, modern molecular research and phylogenetic studies have demonstrated that these similarities are the result of convergent evolution rather than a direct ancestral relationship. It is now understood that flowering plants did not evolve from a gnetophyte ancestor, and the trait of double fertilization evolved independently in both groups.12