– 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.