These algae are mostly macroscopic with undifferentiated cells and originate from a meristem with cell division in three dimensions. In the case of parenchymatous algae, cells of the primary filament divide in all directions and any essential filamentous structure is lost. This tissue organization is found in Ulva (Chlorophyta) and many of the brown algae. Pseudoparenchymatous algae are made up of a loose or close aggregation of numerous, intertwined, branched filaments that collectively form the thallus, held together by mucilages, especially in red algae. Thallus construction is entirely based on a filamentous construction with little or no internal cell differentiation. Palmaria (Rhodophyta) (Figure 1.15) is a red alga with a complex pseudoparenchymatous structure.