Algae spread mainly by the dispersal of spores analogously to the dispersal of Plantae by seeds and spores.
ˈælɡiː spɹˈɛd mˈeɪnli baɪ ðə dɪspˈɜːsəl ʌv spˈoːɹz ɐnˈæləɡəsli tə ðə dɪspˈɜːsəl ʌv plˈæntiː baɪ sˈiːdz ænd spˈoːɹz.