Gymnosperms

Abstract Gymnosperms, also called Acrogymnospermae (1), are a group of seed-bearing plants (spermatophytes) with ovules on the edge or blade of an open sporophyll or ovuliferous scale (Fig. 1). 7eir closest extant relatives are the angiosperms, which have ovules enclosed in a carpel. Gymnospermae is a problematic name because, when fossils are included as is usually the case, the name is widely understood to apply to a paraphyletic group of seed plants from which the angiosperms also arose (1). 7ere are just over a 1000 living species of gymnosperms in the taxa Cycadophyta, Ginkgophyta, Coniferophyta, and Gnetophyta. Here, the relationships and divergence times of families in these phyla are reviewed.