group, so it has been expanded to include the former Spiraeoideae and Amygdaloideae. The subfamily has sometimes been referred to by the name "Spiraeoideae", but this is not permitted by the International Code of Nomenclature for algae, fungi, and plants. Subfamily Dryadoideae: Fruits are achenes with hairy styles, and includes five genera (Dryas, Cercocarpus, Chamaebatia, Cowania, and Purshia), most species of which form root nodules which host nitrogen-fixing bacteria from the genus Frankia. Phylogeny The phylogenetic relationships between the three subfamilies within Rosaceae are unresolved. There are three competing hypotheses: Amygdaloideae basal Amygdaloideae has been identified as the earliest branching subfamily by Chin et al. (2014), Li et al. (2015), Li et al. (2016), and Sun et al. (2016). Most recently Zhang et al. (2017) recovered these relationships using whole plastid genomes: The sister relationship between Dryadoideae and Rosoideae is supported by the following shared morphological characters not found in Amygdaloideae: presence of stipules, separation of the hypanthium from the ovary, and the fruits are usually achenes. Dryadoideae basal Dryadoideae has been identified as the earliest branching subfamily by Evans et al. (2002) and Potter (2003). Most recently Xiang et al. (2017) recovered these relationships using nuclear transcriptomes: Rosoideae basal Rosoideae has been identified as the earliest branching subfamily by Morgan et al. (1994), Evans (1999), Potter et al. (2002), Potter et al. (2007), Töpel et al. (2012), and Chen et al. (2016). The following is taken from Potter et al. (2007): The sister relationship between Amygdaloideae and Dryadoideae is supported by the following shared biochemical characters not found in Rosoideae: production of cyanogenic glycosides and production of sorbitol. Distribution and habitat The Rosaceae have a cosmopolitan distribution, being found nearly everywhere except for Antarctica. They are primarily concentrated in the Northern Hemisphere in regions that are not desert or tropical rainforest. Uses The rose family is considered one of the six most economically important crop plant families, and includes apples, pears, quinces, medlars, loquats, almonds, peaches, apricots, plums, cherries, strawberries, blackberries, raspberries, sloes, and roses. Many genera are also highly valued ornamental plants. These include trees and shrubs (Cotoneaster, Chaenomeles, Crataegus, Dasiphora, Exochorda, Kerria, Photinia, Physocarpus, Prunus, Pyracantha, Rhodotypos, Rosa, Sorbus, Spiraea), herbaceous perennials (Alchemilla, Aruncus, Filipendula, Geum, Potentilla, Sanguisorba), alpine plants (Dryas, Geum, Potentilla) and climbers (Rosa). However, several genera are also introduced noxious weeds in some parts of the world, costing money to be controlled. These invasive