Gymnosperms are embryo forming, vascular tissue containing plants.
These are usually evergreen trees, rarely shrubs and very rarely perennial herbs. Sequoia is one of the tallest trees.
Ginkgo is a living fossil.
The dominant stage in the life cycle is the sporophyte and divided into root, stem and leaf.
The root system is usually a taproot system.
Roots of some plants are associated with fungal mycelia and form Mycorrhizal roots (Pinus), while in others they are associated with Cyanobacteria like Nostoc and Anabaena as in Cycas.
The stem of gymnosperms can be branched (Pinus, Cedrus) or unbranched (Cycas).
Leaves can be simple as in Ginkgo and Gnetum or Pinnately compound as in Cycas.
Leaves persist for a few years and they are well adapted to withstand extremes temperature, humidity and wind.
In conifers like Pinus, the needle-like leaves with sunken stomata and thick cuticle reduce the surface area to minimize water loss (xerophytic adaptation).
Anatomically the stem has Eustele with conjoint, collateral and open vascular bundles.
Xylem usually lacks vessels and companion cells are absent in phloem.
Stem and root show secondary growth.

Reproduction in gymnosperms

Gymnosperms are heterosporous and produce both mega and microspores on the same plant (Monoecious - Pinus) or on different plants (Dioecious – Cycas).
Microspores and megaspores are formed on microsporangia and megasporangia respectively, which in return are formed on microsporophylls and megasporophylls respectively.
The microsporophyll and megasporophyll aggregate and form cone-like structures Strobili.
Megasporophylls possess integumented megasporangium known as ovules which bear female gametophyte.
Female gametophyte possess archegonia i.e. female sex organ.
Microspores include male gametophyte which produces only two male gametes or sperm.
The pollen grains or microspores are liberated at more than 2-celled stage from microsporangium.
Water is not required for transport of male gamete. A pollen tube is formed that delivers male gametes to archegonia.
Fertilization produces a zygote which later turns into an embryo.
Endosperm in gymnosperms is formed before fertilization. It represents the haploid female gametophyte generation.
The seeds are naked i.e. they are not formed inside fruit as in angiosperms.

Classification of Gymnosperms

Gymnosperms are divided into four groups:

1-Cycadopsida- Wood is manoxylic, Siphonogamous fertilization, male gametes are winged, they are commonly called cycads. E.g Cycas

2-Coniferopsida- commonly called conifers, e.g. Pinus. Wood is pycnoxylic, small ephemeral cones formed in groups, large and perennial female cones, siphonogamous fertilization, male gametes non-motile.

3-Ginkgopsida- represented by Ginkgo, also known as maidenhair tree. It is known as a living fossil. It is the only one living organism in this group, it has leathery and fan-shaped leaves, The veins are dichotomously branched, male gametes are motile and multiflagellate.

4-Gnetopsida- includes Gnetum, Ephedra, Welwitschia. Vessels are present in secondary xylem, orthotropous ovules with long tubular micropyle are present, resin canals absent.