The conifers range in age from the Pennsylvanian period of the Paleozoic to the Recent.
Conifers are perennial plants that are highly branched trees and shrubs.
They are characterized by the presence of pycnoxylic wood , highly branched stems with eusteles, bifacial vascular cambia that produce pycnoxylic wood . The tracheids of the secondary xylem are characterized by circular bordered pits on the radial walls . This is an adaptation for wind pollination . The microgametophytes produce non-motile sperm that consist of haploid nuclei. The comparative morphology of the ovulate cones was worked out by Rudolph Florin.