Gymnosperms are naked seeded spermatophytes, originated 350 millions years ago. Most of them have become extinct and some are represented by a few living species called living fossils.e.g. Ginkgo biloba. The main plant body is the diploid sporophyte, which is woody and perennial and differentiated into root, stem and leaves. Sequoia sempervirens is the tallest land plant. The tap roots exhibit association with algae to form corraloid root as in Cycas or with fungi to form mycorrhizal root as I Pinus. The wood is monooxylic as in Cycas or pycnoxylic, lack vessels and wood fibre.
Cycas reproduces asexually by fomtaion of bulbils and by sexual method. It is diocecius, showing sympodial growth in male plants and monopodial growth in female plants. Male plants bear microsporophylls at tip arranged spirally on the cone and group of sporangia in sori are borne on abaxial side of microsporophyll.
Female plants bear megasporophyll arranged in a whorl at the tip. Each megasporophyll bears 1-5 pairs of large. Naked ovules gametophyte or endosperm developed from one of the four megaspores. Female gametophyte contains 2-8 archegonia. Multiflagellated, large spermatozoids formed from haploid microspores (in male palnt) fertilize the egg inside archegonia to form a diploid zygote, which develops into embryo. Cycas shows polyembryony due to presence of more than one archegonia but only one embryo survives.