Gymnosperms

In Gymnosperms (gymnos means naked and sperm means seeds) plants ovules are not enclosed by an ovary wall. The seeds are not covered that is they are naked. Gymnosperms including medium-sized trees or tall size tree and shrubs. Sequoia (redwood tree) is one of the tallest tree species. Some gymnosperms have the fungal association (mycorrhiza in pinus).

In few gymnosperms (cycas) small specialized roots called coralloid roots are associated with N2- fixing cyanobacteria. The stems are unbranched (cycas) or branched (pinus, Cedrus). Gymnosperm leaves may be simple or compound. In cycas, the pinnate leaves persist for a few years. The gymnosperms leaves are well adapted to extreme temperature, humidity, and wind. The needle-like leaves in conifers reduce water loss.

Reproduction in Gymnosperms

The gymnosperms produce haploid microspores and megaspores hence they are called as heterosporous. The strobili bearing microsporophylls and microsporangia are called female strobili or macro sporongiate. In pinus, the male or female cones and megasporophylls are borne on different trees. The megaspore mother cell nucleus is protected by envelopes and the composite structure is called an ovule. The mother cell divides meiotically to form four megaspores (megasporangium). This is developing into a multicellular female gametophyte that bears two or more archegonia or female sex organs. In gymnosperm, the sporangia retained on the sporophyte. But in bryophyte and pteridophytes, male and female gametophyte are independent or free-living existence. After fertilization, a zygote is developing into an embryo and the ovules into seeds. These seeds are not covered.