filamentous (adjective; variant spelling: filamentose) – hair- or thread-like, (1) as applied to the thallus growth form: composed of thin hair-like strands of mycobiont and photobiont, e. g., in Ephebe the photobiont is thread-like surrounded by hyphae or cells of the mycobiont, thus determining the filamentous shape of the lichen thallus; (2) as applied to branching patterns of pendulous thalli: vine-like, i. e., a short main stem that is soon divided into subsymmetrical branches, from which secondary branches are grown by further dichotomy, becoming parallel to each other and often equipped with fibrils. (3) one of several main types of cell organization: several cells in a row that form one single strand, i. e., a filament that is either septate or non-septate, branched or unbranched. In Fungi, cell filaments are commonly called hyphae. Related terms: siphonate, siphonocladate. Kind of:cell organization-type.