Give detailed information about pteridophytes.

(N/A) $\rightarrow$ They are the first terrestrial plants.
$\rightarrow$ Habitat: Pteridophytes are found in cool,damp,and shady places,although some may flourish well in sandy soil conditions.
$\rightarrow$ Body structure: They possess true roots,stems,and leaves.
$\rightarrow$ Vascular tissues: They possess well-developed vascular tissues (xylem and phloem).
$\rightarrow$ Leaves: The leaves in pteridophytes are small (microphylls) as in $Selaginella$ or large (macrophylls) as in ferns.
$\rightarrow$ Life cycle: The main plant body is a sporophyte,which is differentiated into true roots,stems,and leaves.
$\rightarrow$ Reproductive structures: The sporophytes bear sporangia that are subtended by leaf-like appendages called sporophylls. These may form distinct compact structures called strobili or cones (e.g.,$Selaginella$,$Equisetum$).
$\rightarrow$ Spore formation: The sporangia produce spores by meiosis in spore mother cells. The spores germinate to give rise to inconspicuous,small but multicellular,free-living,mostly photosynthetic thalloid gametophytes called prothallus.
$\rightarrow$ Reproduction: Due to the specific requirement of water for fertilization,the spread of living pteridophytes is limited and restricted to narrow geographical regions.
$\rightarrow$ Sex organs: The gametophytes bear male and female sex organs called antheridia and archegonia.
$\rightarrow$ Fertilization: Water is required for the transfer of antherozoids from the antheridia to the mouth of the archegonium. Fusion of the male gamete with the egg results in the formation of a zygote.
$\rightarrow$ Development: The zygote thereafter produces a multicellular,well-differentiated sporophyte,which is the dominant phase.
$\rightarrow$ Homospory vs Heterospory: In the majority of pteridophytes,all spores are of similar kinds (Homosporous,e.g.,$Nephrolepis$). Genera like $Selaginella$ and $Salvinia$ produce two kinds of spores,macro (large) and micro (small) spores,and are known as Heterosporous.
$\rightarrow$ Gametophyte retention: In heterosporous plants,the megaspores and microspores germinate to give rise to female and male gametophytes,respectively. The female gametophytes are retained on the parent sporophytes for variable periods.