The charophycean green algae, which include the Coleochaetales, together with land plants form a monophyletic group, the streptophytes. The order Coleochaetales, a possible sister taxon to land plants, is defined by its distinguishing setae (hairs), which are encompassed by a collar. Previous studies of these setae yielded conflicting results and were confined to one species, Coleochaet. scutata. In order to interpret these results and learn about the evolution of this character, setae of four

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... pecies of Coleochaete and the genus Chaetosphaeridium within the Coleochaetales were studied to determine whether cellulose, callose, and phenolic compounds contribute to the chemical composition of the setae. Two major differences were found in the complex hairs of the two genera. In Chaetosphaeridium the entire seta collar stained with calcofluor indicating the presence of cellulose, while in the four species of Coleochaete only the base of the seta collar stained with calcofluor. In Chaetosphaeridium the seta proper exhibited no internal structures that were detectable with differential interference contrast microscopy or with calcofluor, but did have variable portions that stained with aniline blue indicating the presence of callose. In contrast, setae of the four species of Coleochaete had readily observable internal structures that stained brightly with both calcofluor and aniline blue. More research on Chaetosphaeridium and Coleochaete is necessary to determine if the extensive work on the cell walls of Coleochaete can be generalized to Chaetosphaeridium and whether one genus might be a more appropriate model organism for studying the evolution of plant cell walls.