Gymnosperms represent a heterogeneous group of vascular
plants. One characteristic that traditionally lumps them together
is their production of ovules
that are 'naked' (not enclosed in an ovary).
Living gymnosperms are classified into four divisions, namely,
Cycadophyta (蘇鐵門), Ginkgophyta
(銀杏門), Coniferophyta (Pinophyta
松柏門), and Gnetophyta (賣麻藤門).
Morphological and molecular characteristics, including the flagellate
sperms and nuclear
18s rRNA sequences, suggest that Cycadophyta and Ginkgophyta
are the more primitive groups among gymnosperms. Representatives
of all four divisions of gymnosperms are found
in Hong Kong.