Brown algal walls are composed of cellulose fibrids and the commercially important mucopolysacaride alginic acid . No unicellular or colonial browns, the simplest are the branching filaments , and the longest organism are kelps . Simple filaments form little cellular differentiation while Kelps form lots of cellular differentiation. More complicated forms have cortex and medulla . Cortex is the outer layer of thallus with photosynthetic cells.
Growth is either diffuse or at the meristem .
Meristen is the region where new cell are produced, these can be defined as apical or terminal or interlayer within a branch. In fact simpler forms look alike complex forms look different. Other brown algae have distinctly dissimilar haploid and diploid stages. It is a common filamentous brown, found growing on rocks or large algae. Physodes - vesicles containing poly phenolic compounds, probably unpalatable to most grazers.