Scanning electron micrographs of leaves of British Carex species, 3. Subgenus Carex: sections Vesicariae, Carex, Pseudocyperae, Limosae and Phacocystis

Abstract This part of our series includes about a third of the large and varied subgenus Carex. The sections included are related both in terms of general anatomy and morphology (including leaf-surface characters), and in DNA sequence data. Most are plants of wet habitats. Generally, the sections appear natural on leaf characters except for Carex where C. hirta and C. lasiocarpa have very different leaves. However, all of the species are distinctive in leaf-surface or leaf-section characters. In section Vesicariae, C. vesicaria and C. saxatilis are hypostomous and have smooth surfaces but differ in leaf section, and C. rostrata differs from both in having the stomata predominantly on the upper, papillose surface. In section Limosae, C. limosa has prominent papillae on both surfaces; in C. magellanica, the upper surface is smoother and the lower surface has shorter papillae; C. rariflora differs from both in having amphistomous leaves. These three species all have distinctive stomata. Section Phacocystis is variable in stature, leaf-surface ornamentation, and stomatal distribution, and prone to hybridisation, but has rather uniform and characteristic stomata. Some species are well circumscribed, although variable, e.g. C. aquatilis, C. bigelowii, C. elata, C. acuta, C. cespitosa, and C. nigra. Carex salina appears to consist of a single amphistomous genotype; C. recta is variable in stomatal distribution and seemingly consists of a hybrid swarm which makes its circumscription hard to define.