Systematic significance of fruit morphology and anatomy in tribes Persicarieae and Polygoneae (Polygonaceae)

Fruits of Polygonaceae have a basically similar construction of indehiscent nuts or achenes. Sections of fruits, coupled with surface patterns were st udied with SEM and LM in all genera of the tribes Persicarieae and Polygone ae (Polygonoideae-Polygonaceae). The outer layer of the pericarp is usually thickened and its anatomy can be used consistently to delimit genera more than any other character of the fruit. Cells are most often puzzle piece-sh aped in surface view, but the shape of the cells may become polygonal with straight anticlinal walls towards the endocarp The primary sculpture of the cells is highly variable and has value at the specific level, rarely at th e generic level. No strict correlation exists between the external surface patterns and the anatomy. Two main cell types can be recognized in cross- a nd longitudinal section, correlated with the straight or undulating outline of the anticlinal walls. No distinction can be made between sections Persi caria, Tovara, Echinocaulon, and Cephalophilon of the genus Persicaria; all share narrow rectangular cells with undulating anticlinal walls. Aconogono n and Bistorta can be delimited by the square to rectangular cells with a n arrow dichotomously branching lumen and straight anticlinal walls; both gen era are best grouped as a single genus with two sections. A similar arrange ment is found occasionally in species of Polygonum s.s., Polygonella, Atrap haxis, Fallopia and Calligonum. Fruit anatomy of Pteropyrum is distinctive. The genus Polygonum s.s. shows a wide range of integrating patterns, rangi ng from straight to undulating anticlinal walls and cannot be separated fro m Polygonella. Fagopyrum is aberrant in having a parenchymatic exocarp and a thickened mesocarp; other evidence supports its isolated position. Differ ent fruit anatomical patterns have arisen several times in evolution and ha ve a limited value at tribal level but are useful at generic level. It is s uggested that an arrangement with Straight anticlinal walls and a broad lum en, eventually with dendritic branching towards the periphery, is ancestral . (C) 2000 The Linnean Society of London.