Comparative morphology of Cladopus (including Torrenticola, Podostemaceae) from East Asia to north-eastern Australia

Abstract

Cladopus (with 12 or less species) is an Asian and Australian genus of Podostemaceae–Podostemoideae. They are haptophytes that grow in rivers. The developmental morphology and anatomy of Cladopus austro-osumiensis Y.Kadono & N.Usui, C. austrosatsumensis Koidzumi, C. chinensis Chao, C. japonicus Imamura and C. queenslandicus [Domin] C.D.K. Cook & Rutish. (syn. Torrenticola queenslandica [Domin] Domin ex Steenis) are studied by scanning electron microscope and microtome. The architecture of the examined species fits with the bauplan known from other Asian Podostemoideae. Rosulate shoots arise in zigzag patterns or as opposite pairs from narrow or broad green ribbons which may be interpreted as adhesive creeping roots. Cladopus is the only podostemaceous genus known with both endogenous and exogenous lateral roots along the mother root. Exogenous lobes (which may develop into daughter roots) are next to the sites of root-borne shoots which, finally, give rise to terminal flowers. Cladopus species have the following features (synapomorphies) in common: (1) leaves on older and reproductive shoots with one or two median, long filaments (caducous) and 1–4 lateral short lobes (persistent) on either side of the leaf, which are called stipules; (2) spathella (i.e. mantle-like flower cover) with an apical two-tipped papilla; (3) spathella splitting more or less circumscissilely; (4) capsules globose or nearly so, smooth or with three faint ribs per valve.