Sieve cells are typically associated with gymnosperms, because angiosperms have the more derived sieve tube members and companion cells in their phloem.
It was long thought that the angiosperms arose from within the gymnosperms, but recent molecular evidence suggests that their living representatives form two distinct groups.
For example, enzymes for synthesis of limonene a terpene are more similar between angiosperms and gymnosperms than to their own terpene synthesis enzymes.
It has partially developed vessels as found in the angiosperms, and the megasporangium is covered by three envelopes, like the ovary structure of angiosperm flowers.
