Plant Kingdom - Gymnosperms

Gymnosperms (Greek: $gymnos$ = naked, $sperma$ = seeds) are plants where ovules are not enclosed by an ovary wall and remain exposed both before and after fertilization.

The plant body is a sporophyte ($2n$), differentiated into roots, stems, and leaves. They include the tallest tree species, $Sequoia$ (giant redwood).

Roots are generally tap roots. $Pinus$ exhibits a symbiotic association with fungi called mycorrhiza, while $Cycas$ has specialized coralloid roots associated with $N_2$-fixing cyanobacteria.

Stems may be unbranched (e.g., $Cycas$) or branched (e.g., $Pinus$, $Cedrus$).

Leaves are well-adapted to extremes of climate. In conifers, needle-like leaves, thick cuticle, and sunken stomata help reduce water loss ($H_2O$) by transpiration.

Gymnosperms are heterosporous; they produce haploid microspores ($n$) and megaspores ($n$). These are produced within sporangia borne on sporophylls arranged spirally to form cones or strobili.

Unlike bryophytes and pteridophytes, the male and female gametophytes in gymnosperms do not have an independent free-living existence; they remain within the sporangia retained on the sporophytes.

The endosperm in gymnosperms is formed before fertilization and is always haploid ($n$), unlike angiosperms where it is triploid ($3n$).

Pollination is anemophilous (by wind). Pollen grains are carried by air currents to the mouth of the ovules.