INTRODUCTION
Helictotrichon Besser ex Schult. & Schult.f. (excluding Avenula (Dumort.) Dumort. and Amphibromus Nees) is a genus of temperate C3 grasses with about 40 species (Gibbs Russell et al. 1990; Mabberley 2008). The genus is most diverse in the temperate regions of the northern hemisphere, especially in Europe, from where it extends southwards along the African mountains (Afromontane Region). This paper deals only with those species occurring in southern Africa, a secondary centre of diversity for the genus.
In a taxonomic revision based mainly on macromorphology, Schweickerdt (1937) recognized 12 species of Helictotrichon in southern Africa. A new taxonomic revision of the group (Mashau in progress), which also considered evidence from leaf anatomy, applied to all these species as well as two newly described ones (Mashau et al. 2010), thus bringing the total number of species on the subcontinent to 14. The anatomical attributes of the leaf epidermis of these species were studied for the first time and proved to be particularly useful for distinguishing among species. The purpose of the present paper is to report on the taxonomic significance of leaf epidermal characters in the southern African members of Helictotrichon.
Helictotrichon quinquesetum (Steud.) Schweick. is only known from two collections from the Cape Peninsula, both dating from the 19th century. The species is currently considered critically rare and is probably extinct (Helme & Raimondo 2010). Only fragments of the inflorescence from the type, Ecklon 929 (removed from the holotype in OXF and isotype in K), are available at the National Herbarium (PRE). The original collections are also very poor and have hardly any leaves (seen on Aluka website). Hence, due to the limited material available, this species was not studied anatomically.
MATERIALS AND METHODS
The epidermal structures of 13 Helictotrichon species were studied (see Table 1 for a list of species and voucher specimens). H. quinquesetum, a very rare species, was not studied (see above).
Portions of dried leaf blades were cut from herbarium specimens, transferred to test tubes containing distilled water and heated in a water bath at 50[degrees]C for about 24 hours. After allowing cooling for about 12 hours, the rehydrated leaves were fixed in formalin-acetic-acidalcohol [FAA] (Johansen 1940) for at least 48 hours. Before further processing, the pieces of leaf blade were thoroughly washed in water to remove all traces of the fixative.
To obtain the epidermal peels, leaf blades were transversely cut into pieces of about 10 mm long, and one margin removed by cutting it off. The pieces were placed in stopper glass tubes, covered with Jeffrey's solution [equal volumes of 10% aqueous chromic acid (Cr[O.sub.3]) and 10% nitric acid (HN[O.sub.3])] and left at room temperature for about 24 hours until the unwanted tissue between the upper and lower leaf epidermis had dissociated and was easily freed from the epidermis (Kiger 1971). The sufficiently macerated pieces of leaves were thoroughly washed in water and then stained with 1% safranin in 50% ethanol for about 30 minutes to 1 hour. The stained material was then...