How does plant morphology help in classification?

Hint: Phytomorphology or Plant morphology is the study of physical forms and the external structure of plants. The morphological characters of plants include roots, stem, leaves, flowers, and fruits. These characters are useful for the visual identification of plants.

Complete answer:
Plants are extremely diverse and complex. There are millions of different plant species and many more are yet to be discovered. It is impossible to study all the plants individually so the botanists have divided the plants on the basis of its characters and then placed them into different categories. The morphological characters include distinguishing characters like the type of root system, stem type, inflorescence, flower structure, fruit type, etc. All these characters aid in classification.
Classification of plants on the basis of the root system
Plants have three types of root systems- the Taproot system, Fibrous root system, and Adventitious roots.
The Taproot system consists of a main taproot and other branch roots. The main taproot grows faster than the other branch roots. This type of root system is seen in dicotyledonous plants. Example:- Mustard.
Fibrous root systems have roots of the same size and arise from the base of the stem. This type of root system is seen in monocotyledonous plants. Example:- Wheat.
Adventitious roots are roots that arise from the other parts of the plant other than the radicle. Example:- Grass, Banyan.
Classification of plants on the basis of stem type
Plants can be classified into three types on the basis of stem type ( based on their location with respect to ground):- The underground stem, Aerial stem, and Sub-aerial stem.
Underground stems remain at the ground level. These stems produce aerial shoots that rise above the soil. Their roots are present superficially. These stems store food and are also capable of vegetative propagation.
Aerial stems are stems that are found above the ground and they perform various functions.
Sub-aerial stems run parallel with the ground and give off roots at particular intervals(nodes).
Classification of plants on the basis of inflorescence
The inflorescence is the arrangement of flowers on the floral axis. There are two main types of inflorescences:- Racemose and Cymose.
In racemose inflorescence, the main axis continues growing and the flowers are borne laterally in an acropetal order.
In cymose inflorescence, the main axis gets terminated in the flower and the flowers are borne in a basipetal order.

Additional Information: A leaf can be simple or compound.
When the lamina is entire and when incised, the incisions do not touch the midrib, then the leaf is a simple leaf and when the incisions reach up to the midrib resulting in a number of leaflets then the leaf is a compound leaf.
On the basis of symmetry exhibited, a flower can be divided into Actinomorphic (radially symmetrical) and Zygomorphic (bilaterally symmetrical).
A flower may be trimerous, tetramerous, and pentamerous when the floral appendages are multiples of 3, 4, and 5 respectively.

Note: Anatomy is the study of the internal structure of plants. Till mid- 20^th century, plant anatomy was included in plant morphology but now it's a separate field which refers only to the internal structure of plants. It includes the study of structures of plants on cellular and tissue level through microscopes.