The adventitious roots may be modified to perform various functions such as food storage, mechanical support and some other vital functions. Based on respective function they are classified into three groups.
Of these the first one is the
(i) Storage root:
(a) Tuberous root: Some roots are swollen due to storage of food material. These roots have no definite shape and these are called as tuberous roots. It arises from the lower side of the stem at the nodes. Example: Sweet potato
(b) Fasciculated root: Here the tuberous roots seen as cluster at the base of the base of the stem. Example: Asparagus
(c) Beaded root: The storage roots look as if like a beaded structure i.e. they swell at intervals. Example: Bitter gourd
(ii) Root modified for additional support:
(a) Stilt root: These are the aerial roots which originated from the lowermost node of the stem. This root gives additional support for the main stem. Example: Pandanus.
(b) Prop root: These are the root arising from the stem and they penetrate into the soil and gives thick and stout support.
(iii) Roots modified for vital functions:
(a) Epiphytic root: These are special type of aerial roots which hangs freely in the atmosphere. They are having a special type of tissues known as velamen. Velamen helps in absorbing moisture from the atmosphere without having contact with soil. Example: Orchids
(b) Assimilatory root: Some adventitious roots become green in colour and perform photosynthesis. They are also known as photosynthetic roots. Example: Tinospora
(c) Parasitic root: Parasitic roots or haustoria are the roots seen in non-green parasitic plants. They obtain the nourishment from the host plant through the roots. The roots enter the host plants and makes contact with the conducting tissue. Example: Cuscuta