Ontogenetic studies, sporophyte anatomy and phylogenetic affinities of Phyllothallia nivicola (Phyllothalliaceae, Marchantiophyta)
Authors: Crandall-Stotler, Barbara; Stotler, Raymond E.
Source: Nova Hedwigia, Volume 95, Numbers 3-4, November 2012 , pp. 277-294.
Systematic affinities of the rare, simple thalloid liverwort Phyllothallia E. A. Hodgs. have long been problematic. Hypothesized to comprise two disjunct species, P. nivicola E. A. Hodgs. from New Zealand and P. fuegiana R. M. Schust. from Tierra del Fuego, the genus was initially aligned, albeit remotely so, with either Fossombronia Raddi or Treubia K. I. Goebel. Both placements have proven, however, to be unsupported by molecular phylogenetic analyses, which have consistently resolved Phyllothallia sister to taxa of the suborder Pallaviciniineae. The alignment of Phyllothallia with this suborder is puzzling, especially since anatomical descriptions of immature sporophytes in P. nivicola and mature, but undehisced, sporophytes in P. fuegiana are incongruent with current concepts of sporophyte morphology in the Pallaviciniineae. To re-evaluate the morphological attributes of Phyllothallia, a combination of serial sectioning and SEM methods have been used to generate comparative anatomical data on apical organization, thallus morphology, androecia and gynoecia in P. nivicola and P. fuegiana and describe for the first time anatomical features of mature sporophytes, spores and elaters in P. nivicola. Our findings confirm that Phyllothallia possesses several pallavicinioid characters, including a cuneate apical cell, gynoecia and androecia associated with foliar scales, large rounded sporophyte foot with a multicellular haustorium, and an apically capped capsule. Capsules in P. nivicola have rudimentary basal elaterophores like P. fuegiana, but are ovoid and fundamentally 4-valved, not spheroidal with an irregular dehiscence as previously hypothesized. Spores are cryptopolar and ornamented with two levels of exine sculpturing, and the free elaters possess two terminally closed, spiral-thickening bands. Substantive anatomical differences between P. nivicola and P. fuegiana confirm their recognition as separate species, and the new data reported herein provide evidence of an anatomical link between Phyllothallia and the Pallaviciniineae.