title: Developmental morphology of flattened shoots in Dalzellia ubonensis and Indodalzellia gracilis with implications for the evolution of diversified shoot morphologies in the subfamily Tristichoideae (Podostemaceae).
abstract: OBJECTIVE
  Podostemaceae is a unique family of aquatic angiosperms that grow in swift-running water on rock surfaces in the tropics. Their plant bodies show a remarkable adaptation: the main plant body is mostly creeping or flattened, or in extreme cases foliose, functioning as an adhering and photosynthetic organ. In the subfamily Podostemoideae, the root is foliose, whereas in the subfamily Tristichoideae, the shoot is foliose. An evolutionary scenario for the foliose root has already been proposed, but that for the foliose shoot remains to be addressed.
  
  
  METHODS
  Shoots of Indodalzellia gracilis and Dalzellia ubonensis (subfamily Tristichoideae) were observed using light microscopy and scanning electron microscopy. Gene expression patterns of orthologs of marker genes for the shoot apical meristem, i.e., SHOOT MERISTEMLESS and WUSCHEL, in D. ubonensis were analyzed.
  
  
  RESULTS
  When very young, the phyllotaxis is tristichous in both genera: a set of one dorsal and two marginal leaves forms. When the shoot branches, extra-axillary buds of two subsequent marginal leaves form as new (lateral) shoots, and the original shoot stops growing; this growth pattern is called sympodial branching. Due to zonal growth in the common zone just below the original and lateral shoot apices, flattened or foliose shoots result. The expression patterns of DuSTM and DuWUS in the shoot apices of Dalzellia were similar to those published for Terniopsis.
  
  
  CONCLUSIONS
  The foliose shoots of Indodalzellia and Dalzellia evolved as a result of congenital fusion among several original and lateral branches, each of which grows separately in other Tristichoideae.
authors.affiliation: Department of Chemical and Biological Sciences, Japan Women's University, Mejirodai, Tokyo 112-8681, Japan.
authors.forename: Rieko
authors.initials: R
authors.lastname: Fujinami
authors.affiliation: Department of Chemical and Biological Sciences, Japan Women's University, Mejirodai, Tokyo 112-8681, Japan.
authors.forename: Ryoko
authors.initials: R
authors.lastname: Imaichi
mesh_terms: D005075:Biological Evolution; D018506:Gene Expression Regulation, Plant; D019684:Magnoliopsida / Q000033:anatomy & histology* / Q000235:genetics / Q000254:growth & development* / Q000648:ultrastructure; D008969:Molecular Sequence Data; D018515:Plant Leaves / Q000033:anatomy & histology; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D018520:Plant Shoots / Q000033:anatomy & histology* / Q000235:genetics / Q000254:growth & development* / Q000648:ultrastructure; D036226:Seedlings / Q000033:anatomy & histology; D017386:Sequence Homology, Amino Acid
chemical_list: D010940:Plant Proteins
keywords: Dalzellia ubonensis; Indodalzellia gracilis; Podostemaceae; Tristichoideae; development; evolution; meristem; phyllotaxis; sympodial branching