That seems an innocent and basic question which, in an ideal simple life, can be answered easily.
“A plant is a living thing that grows in the ground, has roots, stems, branches, leaves, flowers, and fruit or berries”. That answer covers the basics, but there is more – much more – to be added if we are to fully describe what a plant is – and in particular all the component parts that combine to make up the plant kingdom – Plantae.
(Plantae is the main ‘family’ name of all living plants.) This family is then divided into the many family groups, or sub-divisions within the main family.
Those who study botany need read no further.
The main plants we are concerned with as gardeners are those which are classified as ‘Vascular Plants’. These plants have a conductive or transport system to move raw materials to and from the different areas of the plant where they are processed into the basic requirements that plants need in order to survive.
A typical garden plant has a root system; stem; branches and leaves which are the main factory and transport links. Flowers and eventually seeds various are also attached in order that they can be fed by the main system.
If the term ‘vascular’ sounds familiar, it may be because human beings and other animals also have a vascular system for transporting goodies – and baddies - around the body
Non vascular plants do not have a factory transport system. These include mosses, fungi and liverworts, which are all plants nonetheless, but have no conductive pathways to move essential moisture and food about. That is the main reason they are to be found in damp shaded areas. They have no stems capable of moving moisture about.
For the purpose of this section, we include grasses, alpines, bulbs, herbaceous and evergreen perennials, ferns, shrubs and trees. Together with these, most houseplants have the same basic structure – as do epiphytic plants of the rain forests; orchids and bromeliads etc. All are vascular plants. Most are seed-bearing. All have the following identifying characteristics – even if they are not immediately visible! These are a root system; stem; leaves; flowers; seeds.
Most plant stems are visible; many are not. The main differential characteristic of a stem is that it has buds, which are situated in its nodal areas. Sometimes the stem is hidden from view – such as with most bulbs. The stem remains within the bulb complete with buds which produce the leaves and flowers which eventually surface for our pleasure. The stem remains underground.
More commonly, the stem is above ground either as a single stem, or as the main support system for lateral stems or branches. In the case of a tree, the stem is normally referred to as the trunk.
Flowers can be male or female, or they can be bisexual – having the male and female parts in within the same flower. Sexual reproduction is the main function of the flower.
Some plants are male others are female, but although rooted to the spot – they cope with the finer details of sexual reproduction!