Comparative leaf anatomy of the Asiatic Myristicaceae

The leaf anatomy of c. 60 species of the four Asiatic genera of the Myristicaceae (Gymnacranthera, Horsfieldia, Knema and Myristica) is described in detail. Myristicaceae have characteristic, uniseriate hairs, the cells of which have arms. The number of arms per cell and the relative length of the arms are important characters to separate the Asiatic genera. The hairs of Knema can be classified further into different types. Many species of Myristicaceae have a layer of cutinaceous, alveolar material overlying the cuticle proper on the abaxial leaf surface. In angiosperms such a layer was hitherto only reported for Winteraceae. Guard cells are often embedded in the subsidiary cells. The paracytic stomatal complex in Knema and Myristica is sunken and overarched by typically arranged bordering cells, leaving a starshaped opening in Knema and forming a ring in Myristica. The vascular system of the midrib is composed of an abaxial and adaxial collateral bundle (the latter is absent from Gymnacranthera). and there are always free phloem bundles in the centre. The diagnostic and taxonomic value of these and many other varying leaf anatomical characters is analysed and discussed. Much of the leaf anatomical variation can be used for species grouping and identification, and the four genera can easily be separated on leaf anatomical characters (see table V, and synoptical keys at the end of this paper). Leaf anatomy lends little support to a close affinity of Myristicaceae with Annonaceae and Canellaceae, and although the family shows several typically Magnolialean characters (e.g. oil cells, paracytic stomata) leaf anatomy points to a fairly isolated position of the family within the order Magnoliales. Many of the leaf anatomical characters of Myristicaceae are highly xeromorphic. This is discussed in relation to the markedly mesic ecology of the family.