Question: Which one, Purshia or Maihuenia, is a small genus of 5-8 species of flowering plants in the family Rosaceae?
Context: Rosales is an order of flowering plants.  It is sister to a clade consisting of Fagales and Cucurbitales.  It contains about 7700 species, distributed into about 260 genera.  Rosales comprise nine families, the type family being the rose family, Rosaceae.  The largest of these families are Rosaceae (90/2500) and Urticaceae (54/2600).  The order Rosales is divided into three clades that have never been assigned a taxonomic rank.  The basal clade consists of the family Rosaceae; another clade consists of four families, including Rhamnaceae; and the third clade consists of the four urticalean families. Physocarpus, commonly called ninebark, is a genus of flowering plants in the family Rosaceae, native to North America (most species) and northeastern Asia (one species). Maihuenia is a genus of cactus (family Cactaceae) and the sole genus of the subfamily Maihuenioideae, which is the smallest subfamily of the Cactaceae.  The genus comprises two cushion-forming, mucilaginous species.  They are found at high elevation habitats of Andean Argentina and Chile. Flemingia is a genus of flowering plants in the legume family Fabaceae.  It is native to Asia and the species are distributed in Bhutan, Burma, China, India; Indonesia, Laos, Malaysia, Nepal, Pakistan, Papua New Guinea, Philippines, Sri Lanka, Taiwan, Thailand and Vietnam.  The genus was founded in 1812.  The number of known species is ambiguous due to taxonomic problems; and is usually enumerated as more than 30.  Burma and China have the highest record of "Flemingia" species with 16 each, followed by India (with 15 species), Thailand (11 species), Laos (10 species), Vietnam (8 species), Bhutan (1 species) and Nepal (5 species). Agrimonia (from the Greek ἀργεμώνη ), commonly known as agrimony, is a genus of 12–15 species of perennial herbaceous flowering plants in the family Rosaceae, native to the temperate regions of the Northern Hemisphere, with one species also in Africa.  The species grow to between .5–2 m tall, with interrupted pinnate leaves, and tiny yellow flowers borne on a single (usually unbranched) spike. Mespilus, commonly called medlar, is a monotypic genus of flowering plants in the family Rosaceae containing the single species "Mespilus germanica" of southwest Asia.  A second proposed species, "Mespilus canescens", discovered in North America in 1990, proved to be a hybrid between "M. germanica" and one or more species of hawthorn, and is properly known as ×"Crataemespilus canescens". Zantedeschia is a genus of 8 species of herbaceous, perennial, flowering plants in the family Araceae, native to southern Africa from South Africa north to Malawi.  The genus has been introduced on all continents except Antarctica.  Common names include arum lily for "Z. aethiopica" and calla and calla lily for "Z. elliottiana" and "Z. rehmannii", although members of the genus are neither true lilies of Liliaceae, true "Arums", or true "Callas" (related genera in Araceae).  They are also often confused with "Anthurium".  The colourful flowers and leaves of both species and cultivars are greatly valued and commonly grown as ornamental plants. Exochorda is a small genus of flowering plants in the family Rosaceae, native to China and central Asia (Turkestan).  They are used as ornamental plants with the common name pearl bush, or pearlbush.  Numerous species have been described on the basis of differing appearance and geographical separation, but a systematic study revealed that the different types are closely related and probably all descended from a single species that formerly had a wide distribution that has been fragmented by habitat loss.  As a single species the correct name is "E. racemosa". Tricarpelema is a genus of monocotyledonous flowering plants in the dayflower family consisting of 8 species.  The genus is divided into two subgenera, subgenus "Tricarpelema", which includes 7 known species found in tropical Asia, and subgenus "Keatingia" with one species in western Africa.  The Asian species are typically found in the forest understory while the single African species has evolved to drier, sunnier conditions and is usually associated with inselbergs. Purshia (bitterbrush or cliff-rose) is a small genus of 5-8 species of flowering plants in the family Rosaceae, native to western North America, where they grow in dry climates from southeast British Columbia in Canada south throughout the western United States to northern Mexico.  The classification of "Purshia" within the Rosaceae has been unclear.  The genus was originally placed in the subfamily Rosoideae, but is now placed in subfamily Dryadoideae.
Answer: Purshia