You can count the spirals because they are coloured.
The left handed spirals are in red and you can count 13.
The rifht hanged spirals are in yellow and you can count 21.
Fibonacci sequence is: 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, ... From 2 the next number is the sum of the two previous numbers:
2 = 1 + 1
3 = 2 + 1
5 = 3 + 2
8 = 5 + 3
13 = 8 + 5
21 = 13 + 8.
Fibonacci numbers are found in many structures in nature.
We have just found that these cacti enclose Fibonacci numbers 13 and 21.
Answer: 13 and 21
