Plurilocular sporangia in ectocarpus asexual reproduction. Oxford University Press. Introduction to the Algae 2nd ed. Whatever their form, the body of all brown algae is termed a thallusindicating that it lacks the complex xylem and phloem of vascular plants. Textbook of Algae. The overall physical appearance of the holdfast differs among various brown algae and among various substrates. Journal of Paleontology. Chemistry and Ecology. Cryptogamie, Algologie. Even in those species that initially produce a single blade, the structure may tear with rough currents or as part of maturation to form additional blades. Giant kelp Macrocystis pyrifera. Botanical Monographs.