Why are xylem and phloem called complex tissues? How are they different from one other?

Explanation

A complex tissue consist of more than one type of cells having a common origin which coordinate to perform a common function. Xylem and phloem are called complex tissues as, they are made up of different types of cells.
Xylem is composed of four different types of cells (elements), namely
(i) tracheids
(ii) vessels
(iii)xylem parenchyma
(iv)xylem sclerenchyma (or fibre).
Phloem is also composed of four different types of elements
(i) sieve tubes
(ii) companion cells
(iii) phloem parenchyma
(iv) phloem fibre
The basic difference between xylem and phloem is listed below