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Download Topic 1 Plant morphology
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Topic 1 Plant morphology 1.1 Overview Plant morphology is the study of those external features of plants used for recognition and classification. That is, it is a collection of words which allow you to describe what the plant looks like. In order to recognise plants, you need to become better acquainted with terminology which will allow you to describe and documents plant parts such as leaves. The words used are part of the universal botanical language that you are starting to learn and these words are understood by all botanists and plants people world wide. Consider this, you have an unknown plant and you wish to determine if it is a plant you want to keep, you may want to know when it will flower or how large it will grow. How do you determine what the plant is, that is, what is its botanical name? There are many good plant recognition and identification books around, many of them have very accurate descriptions of plants and many have wonderful clear photographs. Therefore, for plant recognition to be accurate, and so you can compare the plant you have in front of you to the description in a textbook, you need to be familiar with the botanical jargon which is associated with this science of plant recognition. The main external features that are described are: leaves o shape o arrangement o attachment o apex, base, margin flowers fruit. o shape o arrangement on the plant (inflorescence) 1.2 Typical Plants We can say that a typical flowering plant is composed of: a shoot system consisting of stems bearing leaves, flowers and fruit; a root system. Table 1 - Main functions of the five plant organs of a typical flowering plant. Organ Function roots anchoring plants in the soil absorbing water and nutrients from the soil storage of some food substances a means of vegetative propagation stems supporting leaves, flowers and fruits providing a pathway for movement of substances between the roots and the leaves (translocation) storage of food substances photosynthesis within herbaceous stems a means of vegetative propagation leaves manufacture of food substances by the process of photosynthesis for use by all partsof the plant evaporation of water from leaf surface (transpiration) allowing more water to enter the roots exchange of the gases, carbon dioxide and oxygen, between plant and atmosphere storage of food substances a means of vegetative propagation aesthetic value Organ Function flowers production of seed as a result of pollination and fertilisation aesthetic value fruit protection of seed help in dispersal of seeds 1.3 Monocotyledons and Dicotyledons This group of plants in Class Angiospermae.is divided into two sub-classes: Monocotyledonae (called monocotyledons or monocots). Examples: grasses, palms, orchids, lilies. Dicotyledonae (called dicotyledons or dicots). Examples: roses, petunias, Prunus spp., Eucalypts, Banksias. The table below lists the specific differences between these two groups of flowering plants. Table 2 - Differences between Monocotyledons and dicotyledons. Embryo Monocotyledons Dicotyledons One seed leaf Two seed (cotyledon) leaves (cotyledons) Growth Mostly herbaceous, few absorbent form Roots Herbaceous or woody. Herbs, shrubs, trees The primary The primary root is soon root persists replaced by and becomes adventitious a strong rooots which taproot with form a fibrous smaller root system secondary roots. This forms a taproot system Vascular Numerous 1 ring of system scattered vascular vascular bundles, stem bundles; few differentiating with into cortex and sedcondary pith; thickening secondary thickening common Monocotyledons Dicotyledons Leaf Parallel Network venation venation venation Almost always Margin varied entire Flowers Floral parts Floral parts usually in usually in threes or fours or fives, multiples of or multiples of three 4 or 5 Typical Dicotyledon Plant The figure below shows the basic organs of a ‘typical’ dicotyledon flowering plant and their main functions. Figure 1 - Main function of the plant organs of a ‘typical’ dicotyledon flowering plant. Typical Monocotyledon Plant - Grass Figure 2 - Plant organs of a ‘typical’ grass (monocotyledon) plant. Plant growth patterns When plants grow from seed the first soft growth is herbaceous and is called primary growth. At this stage the roots and shoots are elongating, side branches of both may develop, but there is no woodiness. Diameters remain relatively thin. All annual plants show this stage of growth. Plants which do become woody will also show this in their early development; usually the first wood is not produced until the end of the first growing season. Secondary growth, or woody growth is not seen in monocotyledons, and is only seen in some dicotyledons. All Gymnosperms show woody development. Plants that develop secondary or woody growth are trees, shrubs and some climbers. There is an increase in diameter in both the trunk and the roots that continues for the life of the plant, which is a