Plant Crib
CAREX
For the identification of Carex, the BSBI Handbook Sedges of the British Isles 2nd ed. (Jermy, Chater & David 1982) is essential. A third edition which will describe and illustrate the hybrids is in preparation. The notes below merely emphasize or supplement the information given in the Handbook. References to a series of papers by R. W. David detailing the distribution of most of the rarer species can be found in the Handbook, and recent maps of many species are given in the Scarce Plants and Aquatic Plants. M ost species show great variation in vegetative characters, and fruiting material is often essential for identification. Sterility of utricles, or total non-flowering, is often caused by environmental factors rather than by hybrid origin; non-emergence of the anthers is a more reliable indicator of the latter but some hybrids (e.g. C. divulsa × C. muricata; O'M ahony 1989) regularly have emergent anthers. Abnormalities in the inflorescence are not uncommon and can cause difficulties when using the keys. The groups dealt with are as follows: 1 C. paniculata etc. (p. 342) 6 C. rostrata etc. (p. 346) 2 C. vulpina etc. (p. 343) 7 C. strigosa etc. (p. 346) 349) 3 C. muricata etc. (p. 343) 8 C. flacca etc. (p. 347) 4 C. disticha etc. (p. 344) 9 C. binervis etc. (p. 347) 5 C. acutiformis etc. (p. 344) 10 C. flava etc. (p. 348) Stomata The distribution of stomata on the leaf surfaces can be a very useful identification character. The stomata are arranged in rows, and can usually be seen as minute white dots with the aid of a ×20 or even a ×10 lens. It is especially useful as a field character on fresh specimens, and the stomata become slightly less easy to see in dried material. In the field it is often a much easier character to use than some of the more traditional ones such as the number of stigmas. If a microscope is available, it is a good idea to confirm what you are looking at with a selection of species, either by stripping off bits of epidermis or, more easily, by making an impression of the surface with nail varnish. Generally speaking, the leaf surface with the most stomata becomes concave on drying, so that for example in C. nigra, in which the stomata are mostly confined to the upper surface, the leaf margins roll inwards on drying, while in C. acuta, which has the stomata confined to the lower surface, the leaf margins roll outwards on drying. In hybrids, the distribution of stomata appears to combine that of the two parents, so that, for example, C. × turfosa (C. elata × C. nigra) have stomata abundant on both surfaces. In some species such as C. flacca and C. panicea (in which the stomata incidentally are not diagnostically helpful) it is papillae rather than stomata that show as white dots, but the papillae seem largely confined to the vicinity of the stomata so the character can still be assessed with a lens. The character is especially valuable for distinguishing C. rostrata from C. vesicaria, and from their hybrid; vegetative C. lasiocarpa from C. rostrata; C. bigelowii from C. nigra; and C. acuta from

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