COMPARATIVE MORPHOLOGY OF THE VEGETATIVE STRUCTURES OF TRISTICHA-TRIFARIA, INDOTRISTICHA-RAMOSISSIMA AND DALZELLIA-CEYLANICA (PODOSTEMACEAE, TRISTICHOIDEAE) - A REVIEW

This paper summarizes and elaborates upon previously published investi gations of the comparative morphology of vegetative features of Tristi cha trifaria (Bory ex Willd.) Spreng., Indotristicha ramosissima (Wigh t) van Royen and Dalzellia ceylanica (Gard.) Wight (Podostemaceae, Tri stichoideae) (Jager-Zurn, 1970, 1992, 1995). The architecture of these taxa can be traced to common developmental patterns in angiosperms. A lterations of typical structures within the ''principles of variable p roportions'' contribute to their eccentric appearance. The sympodial b ranching pattern plays a key role for understanding the growth form of these species. A second important feature is the tendency to form coe nosomes (fused shoot axes). In Tristicha trifaria and Dalzellia ceylan ica the vegetative system is complicated by fusion of the proximal par ts of branches from inception with the mother shoots or each other, re spectively. The lichen-like crusts of Dalzellia ceylanica are based on coenosomatic fusion. Tristicha trifaria develops rather intricate for ms by coenosomatic fusion of shoots. These processes, causing a displa cement of the subtending leaves of the respective branches as well as a lateral asymmetry of the stem, are discussed in detail. Tristicha tr ifaria develops upright shoots with elongated internodes and also shoo ts that are crust-like and flattened with short internodes. A dorsiven tral symmetry of shoots becomes more progressively developed working f rom Indotristicha ramosissima to Tristicha trifaria and finally Dalzel lia ceylanica, where it effects a branching only from the flanks of th e unilateral axis, causing a 2-dimensional flattening of the whole sys tem with a specific phyllotaxy and anisophylly. The discussions herein confirm the view of a general conformity of the morphological feature s of Indotristicha ramosissima, Tristicha trifaria and Dalzellia ceyla nica with common features of angiosperms, and support the applicabilit y of the classical root-shoot model to these plants. (C) 1997 Elsevier Science B.V.