The sterile gametophyte as a source of informative characters in the genus Radula (Radulaceae: Hepaticae)

Lack of comprehensive investigation into which characters are informative in the construction of infrageneric classifications prompted this study, which hopes to fill major gaps in the knowledge of character variation and patterns of character state distribution within the genus. In this study, the first part of three, we present the results of our investigation into the sterile gametophyte of 28 primarily austral species of Radula. Several characters identified in previous studies of taxa from different geographical areas are again shown to be variable in the suite of species investigated here, including 1) Stem anatomy, 2) lobule insertion, 3) presence or absence of leaf-free strips, 4) lobe armature, 5) modes of asexual reproduction, 6) the anatomy of lobe cell walls, and 7) oil-body morphology. Attention is brought to two novel characters, 1) the arrangement of slime papillae on the lobule and 2) lobule shape, that may be utilised in future investigation. Attention is also drawn to the oil-bodies of Radula, which despite their uniformity in North American taxa, present a remarkably diverse array of form and number in austral taxa. Radula ratkowskiana possesses two different types of oil-body within each cell, a phenomenon possibly not previously recorded within the Hepaticae. Characters investigated for the first time and found to be uninformative include 1) cell size, which is correlated with plant stature, 2) branch appendage production, which possibly due to their simplicity means developmental patterns perceivable in other groups of hepatics, such as Frullania, are masked in Radula.