 The root system consists of a main sinker root , and up to ten lateral roots extending from a non @-@ lignotuberous root crown . The main sinker root grows straight down to the water table ; it may be up to 15 m ( 49 ft ) long if the water table is that deep . Typically from 3 to 5 cm ( 1 1 ⁄ 4 to 2 in ) in diameter immediately below the root crown , roots become gradually finer with depth , and may be less than half a centimetre ( 0 @.@ 2 in ) wide just above the water table . Upon reaching the water table , the sinker branches out into a network of very fine roots . The laterals radiate out horizontally from the base of the plant , at a depth of 3 – 10 cm ( 1 1 ⁄ 4 – 4 in ) . They may extend over 5 m ( 16 ft ) from the plant , and may bear secondary laterals ; larger laterals often bear auxiliary sinker roots . Lateral roots seasonally form secondary rootlets from which grow dense surface mats of proteoid roots , which function throughout the wetter months before dying off with the onset of summer . 
