Yew (taxus) species - chemical and morphological variations.

The morphological similarities of most Taxus species (Yews) questions the correct identification of many samples of plant material. To determine if real differences exist, authenticated samples were collected from the same Arboretum, at the same time of year. Needles from six Taxus species and 25 varieties of a single species ( T. baccata ) were examined morphologically and chemically for paclitaxel content. The following ranges in results were obtained: needle length (7.7-22.4 mm); needle width (1.3-3 mm); needle area (11.2-48.4 mm 2 ); stomatal pore length (11.1-18.2 µm); stomatal number (82.3-128.9); paclitaxel content (0.002-0.025% of dry weight). Significant intra-specific differences were found to occur between the varieties of T. baccata , but no sufficiently distinctive inter-specific differences of taxonomic value were obvious between the species. Results questioned the identities ascribed to some samples. In general the results appeared to confirm the opinion that taxonomically Yews should be considered as a single species. Morphological comparison of Taxus with samples of the taxonomically related conifers, Cephalotaxus and Torreya , indicated significant microscopical differences in epidermal characteristics, stomatal arrangement, numbers and pore sizes.