BRANCHING DYNAMICS IN CLADINA-SUBTENUIS

The fruticose thallus of mature Cladina subtenuis is characterized by a variable branching pattern. While the shape of the mature thallus is not easily predictable, early branch initiation follows a highly pred ictable pattern. Branching is determined by meristemlike bundles of fu ngal cells located at the apices of the thallus. When the bundles spli t, branching is initiated. Meristem growth is limited to a uniform dev elopmental pattern of dichotomous, sequential divisions of the fungal bundles. Filial meristem bundles, the result of a single division, com prise a developmental unit. Their subsequent divisions, which are sequ ential, produce meristem initials of three or five bundles. Branching is constrained by this pattern, but variability is introduced by the d ifferential elongation and orientation of certain branches. Variabilit y may arise in response to growth conditions such as the proximity of other branches or environmental conditions, for example light availabi lity. The ability to elaborate on the basic plan of development permit s radial expansion and increased photosynthetic opportunities for the thallus of C. subtenuis.