have been published. Phylogenies of several tribes and subtribes have also been published. Compared to previous classifications, more of the tribes and subtribes of Dressler were monophyletic, but not all of them were supported by subsequent studies. In the classification that was published in 2015, the authors expressed doubt about their division of the tribes Orchideae and Vandeae into subtribes. The placement of the genera Pachites, Holothrix, and Hederorkis is especially problematic. The monophyly of the subtribe Cranichidinae is also in doubt. These authors singled out the tribe Podochileae, as well as the subtribes Oncidiinae, Goodyerinae, and Angraecinae as being in special need of phylogenetic study. The basal epidendroids, especially the tribe Gastrodieae, remain poorly sampled in phylogenetic studies. Taxonomy The orchid family (Orchidaceae) is subdivided into five subfamilies, and then into tribes and subtribes. Groups of closely related genera are sometimes referred to informally as alliances. An alliance is a group of taxa, at any taxonomic rank, but usually at the rank of genus or species, that are thought to be closely related. Alliances are designated provisionally and are not recognized in the ICNAFP. The subtribes are formally divided into genera. Some of the genera are divided into subgenera, and some of the subgenera are divided into sections. All of the genera contain at least one species. A special nomenclature is used to name hybrids between different species. About 150 species and about a dozen new genera were described each year from 2000 to 2015. According to Dressler, there are 5 subfamilies, 22 tribes, 70 subtribes, and about 850 genera of orchids. When he published his classification, only about 20,000 species of orchids were known. Several thousand have been described since then. A distinction between monandrous flowers and others is especially important in the classification of orchids. A monandrous flower is one that has only a single stamen. The flowers are monandrous in the subfamilies Vanilloideae, Orchidoideae, and Epidendroideae. Like many others before him, Dressler believed that the monandrous orchids form a monophyletic group. It is now known that monandry arose twice in the orchids, once in Vanilloideae, and again in the common ancestor of Orchidoideae and Epidendroideae. The other subfamilies, Apostasioideae and Cypripedioideae, have either three stamens or two stamens and a staminode. The following subfamilies are recognized: Subfamily Apostasioideae: monophyletic - the most basal of the orchids: three fertile anthers, or two fertile anthers and a filamentous