Question: Dahlia and Aruncus are both examples of what type of plant catagorization?

Context:
List of Dahlia species
There are 42 accepted species in the "Dahlia" genus, according to The Plant List.
 The sectional classification of "Dahlia " "sensu" Sørensen (1969) as updated by Saar "et al." (2003) and Hansen (2004) and (2008) is as follows (excluding infraspecific taxa);
Aruncus
Aruncus is a genus of clump forming herbaceous perennial plants in the family Rosaceae.
 Botanical opinion of the number of species differs, with from one to four species accepted.
 They are closely related to the genera "Filipendula" and "Spiraea", and are native to mountainous damp woodland in temperate regions of the Northern Hemisphere.
 Creamy white plumes of flowers are produced above veined and toothed leaflets.
Aruncus dioicus
Aruncus dioicus (Walt.)
 (known as goat's beard, buck's-beard or bride's feathers) is a flowering herbaceous perennial plant in the family Rosaceae, and is the type species of the genus "Aruncus".
 It has alternate, pinnately compound leaves, on thin, stiff stems, with plumes of feathery white or cream flowers borne in summer.
 This plant can be found in moist woodland, often at higher altitudes, throughout temperate areas of Europe, Asia, and eastern and western North America.
 In the UK it is considered suitable for planting in and around water areas, and has gained the Royal Horticultural Society's Award of Garden Merit.
Tuber
Tubers are enlarged structures in some plant species used as storage organs for nutrients.
 They are used for the plant's perennation (survival of the winter or dry months), to provide energy and nutrients for regrowth during the next growing season, and as a means of asexual reproduction.
 "Stem tubers" form from thickened rhizomes (underground stems) or stolons (horizontal connections between organisms).
 Common plant species with stem tubers include potato and yam.
 Some sources also treat modified lateral roots ("root tubers") under the definition; these are encountered in sweet potato, cassava, and dahlia.
List of Dahlia cultivars
The horticultural cultivation of the dahlia plant has resulted in over 57,000 registered cultivars of dahlia.
 Several of them are listed below.
Dahlia
Dahlia ( or ) is a genus of bushy, tuberous, herbaceous perennial plants native to Mexico.
 A member of the Asteraceae (or Compositae), dicotyledonous plants, related species include the sunflower, daisy, chrysanthemum, and zinnia.
 There are 42 species of dahlia, with hybrids commonly grown as garden plants.
 Flower forms are variable, with one head per stem; these can be as small as 2 in diameter or up to 1 ft ("dinner plate").
 This great variety results from dahlias being octoploids—that is, they have eight sets of homologous chromosomes, whereas most plants have only two.
 In addition, dahlias also contain many transposons—genetic pieces that move from place to place upon an allele—which contributes to their manifesting such great diversity.
Dahlia 'Bishop of Llandaff'
"Dahlia" 'Bishop of Llandaff' is a branching, tuberous tender perennial cultivar with dark eggplant-colored, almost black, foliage.
 This produces a stunning contrast with its scarlet flowers.
 The plant was first bred by Fred Treseder, a Cardiff nurseryman.
 It was selected by and named to honour Joshua Pritchard Hughes, Bishop of Llandaff, in 1924 and won the RHS Award of Garden Merit in 1928.
 The plant is about 1 m tall and flowers from June until September.
 As with all dahlias, frost blackens its foliage, and its tubers need to be overwintered in a dry, frost-free place.
Dahlia imperialis
Dahlia imperialis or Bell tree dahlia is an 8-10 metre tall member of the Dahlia genus native to Mexico, Central America and Colombia.
 It is a plant of the uplands and mountains, occurring at elevations of 1500 - , and its leaves are used as a dietary supplement by the Q'eqchi' people of San Pedro Carchá in Alta Verapaz, Guatemala.
Ayla-Axum amphorae
The Ayla-Axum amphorae are narrow conical amphoras that were named after the widest range of finds in the Red Sea.
 Subsequent findings since the mid- 1990s indicate, however, that the amphoras originate in Byzantine, or even early Islamic, Aqaba.
 Hence, the preferred nomenclature is now "Aqaba Amphora."
 The Ayla-Axum/Aqaba amphora type has parallels from at least three terrestrial sites in Eritrea and Ethiopia: Aksum, where amphora sherds with gray fabric were found by the Deutsche Aksum Expedition (Zahn 1913: 208); Matara dating to the 4th through 7th centuries (Anfray 1990: 118); and Adulis (Paribeni 1907: 551) examples of which are on display in the National Museum in Asmara.
 Other examples have been found at Berenike in Egypt, where the amphoras date firmly to an early 5th century context in what may be the best stratified examples (Hayes 1996: 159-61); from Aqaba in Jordan where many examples have been found, including their kilns; on The Shipwreck at Black Assarca Island, Eritrea (Pedersen 2008; Pedersen 2000); and in the Mediterranean such as on the late 6th-century shipwreck at Iskandil Burnu, Turkey, as well as in Spain and Carthage in strata datable from the mid-fourth to the sixth centuries (Keay 1986: 356, 358, 471).
 The largest number (c. 500) came to light during excavations at Zafar/Yemen.
Dahlia pinnata
Dahlia pinnata ("D. x pinnata") is a species in the genus "Dahlia", family Asteraceae, with the common name garden dahlia.
 It is the type species of the genus and is widely cultivated.

Answer: genus