Sentence:  In Lejeuneaceae vegetative branches normally originate from the basiscopic basal portion of a lateral <WSD>segment</WSD> half, as in the Radulaceae, and the associated leaves, therefore, are quite unmodified. 
Meaning of the word marked with <WSD> tags:  A portion of an organ whose cells are derived from a single cell within the primordium from which the organ developed.