| Summary: | Indumentum types of the leaves in 31 species of Potentilla L. (Rosaceae) and four related genera, especially Tylosperma Botsch., Schistophyllidium (Juz. ex Fed.) Ikonn., Drymocallis Fourr. ex Rydb., and Sibbaldia L. from Iran were investigated. Indumentum ultrastructure was studied by scanning electron microscopy (SEM). SEM observation revealed three type classes based on leaf indumentum: 1) straight (appressed-erect); 2) straight-erect and crispate, and 3) crispate-floccose. The straight hair character (I type class) is widely distributed among all genera sampled and six sections of Potentilla. In contrast the crispate-floccose indumentum (III type class) is confined to all examined species of sections Speciosae and Pensylvanicae. While some sections especially Rectae (straight and straight-crispate hairs) and Terminales (straight-crispate and floccose-crispate) posses two indumentum type classes. The present survey shows that indumentum types are of systematic importance and may form good key characters for identification purposes.
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