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Why were gnetophytes once thought to be closely related to flowering plants?

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Gymnosperm Pine cone and exposed seeds of the pinyon pine (*Pinus edulis*). Pinyon pines are gymnosperms and bear their edible seeds, known as pine nuts, in protective cones instead of fruit.

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

Proponents of this relationship cited the following key similarities:
* Reproductive structures: The compound nature of their pollen-producing and seed-producing strobili led some botanists to interpret these structures as "inflorescences" or flowers.1
* Vascular tissue: Unlike other gymnosperms, gnetophytes possess vessels in their xylem (wood), a feature characteristic of angiosperms.1
* Double fertilization: The presence of a unique system of double fertilization in gnetophytes was historically used to suggest a close evolutionary link to flowering plants, though modern research has shown this trait evolved independently in both groups.2

In recognition of these similarities, some earlier classification systems placed gnetophytes in a group called Chlamydospermae, positioned between gymnosperms and angiosperms. However, most modern botanists reject this, and molecular DNA studies have established that flowering plants did not evolve directly from a gnetophyte ancestor.1