Plant Kingdom

• The Five Kingdom classification proposed by Whittaker (1969) includes Monera, Protista, Fungi, Animalia, and Plantae
• Fungi, members of Monera, and Protista with cell walls have been excluded from Plantae in the current classification
• Cyanobacteria, also known as blue-green algae, are no longer considered algae
• Algae are chlorophyll-bearing, simple, thalloid, autotrophic, and largely aquatic organisms
• Algae can be found in various habitats such as moist stones, soils, wood, and can also form associations with fungi and animals
• Algae reproduce through vegetative, asexual, and sexual methods
• Green algae (Chlorophyceae) are commonly unicellular, colonial, or filamentous with chlorophyll a and b as dominant pigments
• Brown algae (Phaeophyceae) are primarily found in marine habitats, ranging from simple branched forms to large kelps
• Red algae (Rhodophyceae) are marine organisms with red pigment r-phycoerythrin, storing food as floridean starch
• Bryophytes, including mosses and liverworts, are called amphibians of the plant kingdom and are dependent on water for sexual reproduction
• Bryophytes lack true roots, stem, or leaves, and their main plant body is haploid, known as a gametophyte
• Liverworts grow in moist, shady habitats and have thalloid plant bodies, with asexual reproduction through fragmentation or gemmae formation
• Sexual reproduction in liverworts can take place by fragmentation of thalli or by the formation of specialized structures called gemmae
• Gemmae are green, multicellular, asexual buds that develop in small receptacles called gemma cups located on the thalli
• During sexual reproduction in liverworts, male and female sex organs are produced either on the same or on different thalli
• The sporophyte in liverworts is differentiated into a foot, seta, and capsule, with spores being produced within the capsule after meiosis
• In mosses, the predominant stage of the life cycle is the gametophyte, which consists of two stages: protonema and leafy stage
• Protonema is a creeping, green, branched, and frequently filamentous stage that develops directly from a spore
• The leafy stage develops from the secondary protonema as a lateral bud, consisting of upright, slender axes bearing spirally arranged leaves
• Vegetative reproduction in mosses is by fragmentation and budding in the secondary protonema
• In sexual reproduction in mosses, the sex organs antheridia and archegonia are produced at the apex of the leafy shoots
• The sporophyte in mosses is differentiated into a foot, seta, and capsule, with spores being formed after meiosis within the capsule
• Pteridophytes include horsetails and ferns, and they are the first terrestrial plants to possess vascular tissues – xylem and phloem
• The main plant body in pteridophytes is a sporophyte, differentiated into true root, stem, and leaves, with well-differentiated vascular tissues
• In pteridophytes, the leaves may be small (microphylls) as in Selaginella or large (macrophylls) as in ferns
• The sporophytes in pteridophytes bear sporangia that produce spores through meiosis, which germinate to form free-living, mostly photosynthetic thalloid gametophytes called prothallus
• Pteridophytes are further classified into four classes: Psilopsida (Psilotum), Lycopsida (Selaginella, Lycopodium), Sphenopsida (Equisetum), and Pteropsida (Dryopteris, Pteris, Adiantum)
• Gymnosperms are plants in which the ovules are not enclosed by any ovary wall and remain exposed, both before and after fertilization
• Gymnosperms produce haploid microspores and megaspores within sporangia borne on sporophylls, arranged spirally along an axis to form lax or compact strobili or cones
• The pollen grain develops into a male gametophytic generation called a pollen grain, which carries the male gametes and is released from the microsporangium
• Following fertilization in gymnosperms, the zygote develops into an embryo and the ovules into seeds, which remain uncovered
• Angiosperms, or flowering plants, have pollen grains and ovules developed in specialized structures called flowers, with seeds enclosed in fruits
• Angiosperms are divided into two classes: dicotyledons and monocotyledons