Zygotes of fucoid algae acquire polarity de novo. The initial polarity establishes the apical-basal polarity of the multicellular embryo and the adult plant. Acquisition of polarity involves the translation of external vectorial signals into spatial information within the cell via spatial photoreceptor activation at the level of the plasma membrane. Fixation of the polar axis involves interactions between the cytoskeleton, plasma membrane and the cell wall. Recently a central role for targeted secretion in polar axis fixation has been identified. In the multicellular embryo, evidence is accumulating for roles of cell wall and intercellular communication via diffusible signals in pattern formation and control of cell fate.