– Evolution of plants is thought to have started in water
– the most primitive plant forms are represented by algae
– this are structurally simple plants
– exhibit of wide range of structural complexity
– range from unicellular, filamentous, colonial to thalloid forms
– All possess the basic plant characteristics, such as pigment (photosynthesis), cellulose cell wall (for rigidity and support) as subcellular membrane bound organelles
– they however, lack pronouncing tissue differentiation
– unicellular forms are simplest and do not show specialization in vegetative or reproductive parts e.g chlorella, euglena, etc
– filamentous and colonial forms ( e.g Spirogyra and volvox respectively) still do not show any marked differentiation and specialization of parts
– thalloid forms (e.g fucus, laminaria), most complex
– exhibit some degree of specialization in vegetative or reproductive parts
– most advanced group
– tissue differentiation, though very little resemble that found in early land plants
– all algae are entirely dependent on water for growth and reproduction
– early land plants are bryophytes
– include the liverworts and mosses
– these are not entirely independent on water for reproduction and growth
– limited to moist habitat and are more structurally complex than algae
– show a little more advanced degree of differentiation of tissue and
-specialization of vegetative/reproductive parts, alternation of generation (gametophyte is dominant)
– still largely dependent on water for reproduction
– no true stem, root or leaves but have equivalent structures (rudimentary)
– due to poor internal transport system (vascular system) growth is prostrate and restricted to moist shady area
– Pteridophyte (e.g ferns) at more complex and advanced show prostrate, semierect or climbing stem
– sporophyte is dominant
– have simple parenchymatous leaves and small fibrous root
– possess fertile leaves/fronds are specialized for reproduction. Heterosporous  in habit
– vascular tissues are fairly well developed, with xylem, phloem, etc.
– specialization of sporophytes and differentiation of tissue permit reduced dependence on water
– seed formed habit at rudimentary level
– spermatophytes: (seed bearing plant) are represented by the gymnosperms and angiosperms
– considered the most advanced
– development of seed habit and increased complexity of vascular system in the sporophyte enabled almost complete independence from water
– dominant land flora today
– flowering habit of the angiosperm more advanced than cone bearing habit of gymnosperms.
– angiosperms seed enclosed in carpel are more advanced than naked seed of gymnosperms
– flower production increasing chances of reproduction by attracting diverse pollinating agents
– angiosperm  most wide spread of spermatophytes colonized different ecological habitat
– developed different growth habits/forms e.g grasses, herbs, shrubs, hydrophytes, trees, etc.
– angiosperm traditionally subdivided into monocots and dicots depending on growth pattern and specialized characteristic of flora and vegetative parts.