The superasterids are a major clade of flowering plants within the core eudicots. In the APG IV system of flowering-plant classification, the clade comprises Berberidopsidales, Santalales, Caryophyllales, and the large clade known as the asterids. The superasterids include more than 90,000 described species; the asterids alone contain more than 80,000 species. APG IV recognizes 20 orders and 146 families within the superasterids. Subsequent plastid and nuclear phylogenomic studies broadly support this circumscription, although the branching order of several early-diverging lineages and the limits of some families remain subjects of research. Members of the clade are extraordinarily diverse in form and ecology. They include forest trees, shrubs, vines, annual and perennial herbs, aquatic plants, desert succulents, carnivorous plants, epiphytes, and both partially and completely parasitic plants. Familiar superasterids include asters, daisies, sunflowers, lettuces, carrots, celery, coffee, tea, potatoes, tomatoes, sweet potatoes, olives, mints, heaths, blueberries, cacti, carnations, beets, spinach, quinoa, buckwheat, sandalwoods, mistletoes, and numerous ornamental plants. The name is based on Asteridae, a name historically used for a subclass or other high-ranking group of flowering plants. In APG IV, “superasterids” is an informal, unranked clade name rather than a traditional Linnaean rank.
Circumscription and nomenclature The modern concept of the superasterids developed from molecular studies of flowering-plant relationships. Earlier classifications based mainly on morphology generally treated the major constituent groups (particularly the traditional Asteridae, Caryophyllales and Santalales) as separate assemblages whose close relationship was not apparent. Multigene analyses showed that these groups belong to a larger branch of the core-eudicot tree. Soltis and colleagues formally named Superasteridae in 2011, defining it as the most inclusive crown clade containing an asterid exemplar but not a rosid exemplar. Their analysis included Berberidopsidales, Santalales, Caryophyllales, Asteridae, and, under that particular topology the Dilleniaceae; other analyses placed Dilleniaceae elsewhere. APG IV subsequently introduced the lowercase informal names “superasterids” and “superrosids” for the two large clades dominated by asterids and rosids, respectively, and treated Dilleniales separately. Because the superasterids are unranked, the name does not denote a fixed Linnaean category such as subclass or superorder. The capitalized form Superasteridae belongs to phylogenetic-nomenclature usage, whereas the lowercase “superasterids” follows APG IV's convention for informal clade names. APG IV also recognized several superasterid orders that had not been accepted as separate orders in APG III, including Boraginales, Icacinales, Metteniusales, and Vahliales. Their recognition reflected improved resolution of relationships among the lamiids.
Diversity and characteristics The superasterids are diagnosed primarily by common ancestry rather than by a single readily visible morphological synapomorphy. Their constituent lineages diverged early enough that many structural and chemical characters have been modified, reduced, or independently evolved. Nevertheless, broad evolutionary patterns characterize major parts of the clade. As members of Pentapetalae, superasterids descend from plants with an ancestrally five-parted, whorled floral organization. Five sepals and five petals remain common, but departures are frequent: flowers may have four parts, numerous parts, fused organs, strongly reduced structures, or no conspicuous petals. The four principal lineages display markedly different combinations of features:
Berberidopsidales Berberidopsidales is a small lineage containing two families of woody plants, Aextoxicaceae and Berberidopsidaceae. Its living species occur in South America and eastern Australia. The two families were not generally regarded as close relatives before molecular analyses placed them together among the early-diverging superasterids. Santalales Santalales includes sandalwoods, mistletoes, and their relatives. Most species are parasitic, including both photosynthetic hemiparasites and non-photosynthetic holoparasites. They connect to host tissues through specialized organs called haustoria; hemiparasites obtain principally water and mineral nutrients from hosts, whereas holoparasites also depend on hosts for organic carbon. The order includes root and stem parasites ranging from herbs and vines to shrubs and trees. Caryophyllales Caryophyllales is morphologically and ecologically diverse. It includes cacti and many other succulents, carnations, beets, spinach, amaranths, quinoa, buckwheats, tamarisks, sundews, Venus flytraps, and tropical pitcher plants. Its members occupy deserts, salt marshes, alpine regions, tropical forests, aquatic habitats, and nutrient-poor wetlands. Carnivory evolved repeatedly within the order, while extreme succulence and drought or salt tolerance characterize other lineages. Many members of the core Caryophyllales produce red or yellow betalain pigments in place of the anthocyanin pigments used by most other flowering plants. Asterids The asterids form by far the largest superasterid lineage. Their flowers frequently have petals fused into a tubular or bell-shaped corolla (sympetaly), often with stamens attached to the corolla. Other recurring features include unitegmic or otherwise reduced ovules, tenuinucellate ovules, and iridoid compounds, although none of these characters is universal across the clade. The asterids include such large families as Asteraceae, Rubiaceae, Lamiaceae, Apocynaceae, Ericaceae, Gesneriaceae, Solanaceae, and Apiaceae. Within the asterids, Cornales and Ericales are the earliest-diverging major branches. Most remaining species belong to the euasterids, which are divided into two large clades, the lamiids and the campanulids. Lamiids include the mint, olive, potato, tomato, coffee, gentian, milkweed, borage, and morning-glory families. Campanulids include the holly, daisy, bellflower, carrot, ginseng, honeysuckle, and viburnum families.
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