Plant Kingdom — Class 11 Biology

This chapter classifies Kingdom Plantae into algae, bryophytes, pteridophytes, gymnosperms and angiosperms, and explains how classification has moved from artificial systems based on a few characters to natural and phylogenetic systems. Algae are simple, chlorophyll-bearing, largely aquatic thalloid autotrophs that reproduce by fragmentation, spores and gametes (isogamous, anisogamous or oogamous); they are divided by pigment and stored food into Chlorophyceae (green), Phaeophyceae (brown) and Rhodophyceae (red). Bryophytes, the amphibians of the plant kingdom, depend on water for sexual reproduction; their dominant plant body is a haploid gametophyte, and they include liverworts and mosses. Pteridophytes are the first plants with true vascular tissue; their dominant phase is the sporophyte, and many are homosporous while some, like Selaginella, are heterosporous, foreshadowing the seed habit. Gymnosperms bear naked seeds not enclosed in an ovary and are heterosporous, with male and female cones and reduced gametophytes retained on the sporophyte. Angiosperms produce flowers, enclose seeds in fruits, and are divided into dicotyledons and monocotyledons. A recurring theme is alternation of generations between haploid gametophyte and diploid sporophyte phases, whose relative dominance shifts across these groups.