terms of the number of species, Orchidaceae diversification is remarkable. However, although the other Asparagales may be less rich in species, they are more variable morphologically, including tree-like forms. Boryaceae to Hypoxidaceae The four families excluding Boryaceae form a well-supported clade in studies based on DNA sequence analysis. All four contain relatively few species, and it has been suggested that they be combined into one family under the name Hypoxidaceae sensu lato. The relationship between Boryaceae (which includes only two genera, Borya and Alania), and other Asparagales has remained unclear for a long time. The Boryaceae are mycorrhizal, but not in the same way as orchids. Morphological studies have suggested a close relationship between Boryaceae and Blandfordiaceae. There is relatively low support for the position of Boryaceae in the tree shown above. Ixioliriaceae to Xeronemataceae The relationship shown between Ixioliriaceae and Tecophilaeaceae is still unclear. Some studies have supported a clade of these two families, others have not. The position of Doryanthaceae has also varied, with support for the position shown above, but also support for other positions. The clade from Iridaceae upwards appears to have stronger support. All have some genetic characteristics in common, having lost Arabidopsis-type telomeres. Iridaceae is distinctive among the Asparagales in the unique structure of the inflorescence (a rhipidium), the combination of an inferior ovary and three stamens, and the common occurrence of unifacial leaves whereas bifacial leaves are the norm in other Asparagales. Members of the clade from Iridaceae upwards have infra-locular septal nectaries, which Rudall interpreted as a driver towards secondarily superior ovaries. Asphodelaceae + 'core Asparagales' The next node in the tree (Xanthorrhoeaceae sensu lato + the 'core Asparagales') has strong support. 'Anomalous' secondary thickening occurs among this clade, e.g. in Xanthorrhoea (family Asphodelaceae) and Dracaena (family Asparagaceae sensu lato), with species reaching tree-like proportions. The 'core Asparagales', comprising Amaryllidaceae sensu lato and Asparagaceae sensu lato, are a strongly supported clade, as are clades for each of the families. Relationships within these broadly defined families appear less clear, particularly within the Asparagaceae sensu lato. Stevens notes that most of its subfamilies are difficult to recognize, and that significantly different divisions have been used in the past, so that the use of a broadly defined family to refer to the entire clade is justified. Thus the relationships among subfamilies shown above, based on APWeb , is somewhat uncertain. Evolution Several studies have attempted