Morphology and anatomy of fruits in Pouzolzia (Urticaceae) in relation to taxonomy

The pericarp and perianth in fruits of 27 of the 35 currently accepted species of the genus Pouzolzia (Urticaceae) were studied. The pericarp is crustaceous and always entirely sclerified. Cell walls are impregnated with silica, lignin and/or tannins, colouring the pericarpium. Cells of the innermost mesocarp layer have amorphous solid contents. Pericarp structure is of a consistent basic pattern throughout the genus. The fruiting perianth is crustaceous and generally easy to detach from the pericarpium. Fruiting perianth structure is much more variable than pericarp structure, differing not only between species but sometimes also within a species or an individual plant, giving rise to fruit polymorphism in certain taxa. Outgrowths of the perianth give rise to surface sculpture, ribs, or wings. Fruits were classified into seven groups on the basis of the number and structure of pericarp cell layers, the presence and distribution of tannins and the structure of the innermost mesocarp layer. These seven groups of species differ from one another also in fruiting perianth anatomy: the groups correlate well with classification based on gross morphology. Characters of both perianth and pericarp clearly support the distinction between the genera Pouzolzia, Boehmeria and Pipturus. Within Pouzolzia they also support the distinction between sections Pouzolzia and Memorialis. Certain adaptive features are discussed and evolutionary trends suggested.