An unbranched epidermal outgrowth, e.g. a hair, a papilla; in cyanobacteria, a single row of cells in a filamentous colony.
A trichome is a row of cells which have remained attached to one another following successive cell divisions. The cells in the trichome are usually separated by septa but some of the adjacent cells can communicate with one another via small pores (microplasmodesmata) which are not found in a simple chain of bacterial cells such as chains of streptococci. The cells of a trichome may or may not be covered by a common sheath. Trichomes are formed by many cyanobacteria and e.g. by species of Beggiatoa.