nomenclature The splitting of Aster the increasingly widespread acceptance / RHS Sandall Tim of classification changes in Aster will result in new names for Michaelmas daisies and their relatives In 2015 the RHS had all been regarded as part of the genera and 25,000 species. By the large genus Aster, which at one time second edition in 2007 the number will adopt the new contained about 500 species. of genera had increased by about scientific name for 500 to 1,600 while the number of Shrinking genera species remained about the same. Michaelmas daisies, In recent years, taxonomists have What has been the impact of this as well as other removed clusters of species from trend on the names we use in the large genera in the Asteraceae to form garden? Many of us can remember changes in Aster. smaller, more easily comprehensible when what we now know as Julian Shaw units. The table below shows the Brachyglottis ‘Sunshine’ was Senecio general shrinkage of several large ‘Sunshine’. We have also come to explains why Asteraceae genera as more numerous, accept Brachyscome rather than smaller genera have been established Senecio for a genus of bedding plants, ichaelmas daisies are or expanded. The figures given in the Felicia instead of Aster for those blue perhaps the most familiar two editions of Heywood (1978, South African daisies, and Argyranth- M plants currently grown 2007) summarize the situation. In emum rather than Chrysanthemum for under the Aster label. Mainly cultivars 1978 the first edition recorded 1,100 bedding marguerites. of A. novae-angliae and A. novi-belgii, they are a key element in gardens, changes in number of species in large astErAcEAE genera giving colour to bright autumn days 1973 1994 2008 2011 in the northern hemisphere. There Aster 500 250 180 152 are many cultivars available, in a wide Eupatorium 1,200 48 41 45 Senecio 2,000–3,000 1,250 1,000 1,200 range of shades including white, Vernonia 1,000 500 750 17 blue, purple, pink and shades of red. Sources: Willis (1973), Bremer (1994), Mabberley (2008), Shiet al. (2011). Until recently, Michaelmas daisies 120 June 2014 PlantsmanThe Why the changes? will be given in the book, and it is Many of the large genera traditionally hoped that the horticultural industry accepted in flowering plants are and gardeners will become familiar assemblages of species left over after with and use the new names. more distinctive clusters of species have been removed. This includes Aster reshapes the horticulturally important Aster The type species of the genus Aster and Senecio. Rather than consisting is Aster amellus, a south European of homogenous units linked by species sometimes known as Italian characters held in common, these aster. This is the species to which genera tend to be artificial groupings the name of the genus is permanently holding the less distinctive remnants Sleigh / RHS Mike linked. This means that if the genus of a tribe. In effect, these large genera Aster amellus is the type species of the genus, so is split up then A. amellus (and its of remnants represent unfinished will retain its name, along with its close relatives closest relatives) is the species that taxonomic business. This is not the opposed to superficially similar, are keeps the Aster name. Other garden best way to construct a useful grouped together. Hence the plants that keep the Aster name taxonomy. While there have been classification is more useful, include European species such as several attempts to propose division particularly in areas that rely on the A. thomsonii and its hybrid with of these large genera into smaller predictive nature of taxonomy, such A. amellus, A. x frikartii. Aster pyrenaeus units, they have not been upheld by as conservation, plant breeding and also keeps its name. Incidentally, the more recent molecular data. the search for natural products. In cultivar ‘Lutetia’ which is often listed Although a certain amount of reality, the problem lies not with the under A. pyrenaeus, appears to progress in understanding new classification and new names, represent a selection of A. amellus relationships between species in but in the limited knowledge and (Picton 2004). Aster was made using morphology mistaken ideas of the past that can Aster tripolium, sea aster, a UK and chromosome morphology (Jones tenaciously hold us in their grip. native, becomes Tripolium 1980, 1983; Semple & Brouilllet pannonicum, the only species in its 1980), it was only after studies Coming soon genus. Aster sedifolius has become analyzing variation in chloroplast The new classification of Aster has part of the Eurasian genus Galatella, and nuclear DNA that real progress been used in the recent Flora of consisting of 40–50 species. began (Xiang & Semple 1996). More North America (Barkley et al. 2006) Some Asiatic species, including recent work has focused on nuclear and Flora of China (Shi et al. 2011), A. glehnii and A. dimorphophyllus ribosomal DNA internal transcribed and is appearing in new regional from Japan, and A. taiwanensis from spacer (ITS) sequences, such as a floras in America such as the Flora of Taiwan, are likely to form new genera. study by Brouillet et al. (2001) that Missouri (Yatskievych 2005), and A recent study by Li et al. (2012) has employed data from 326 accessions. also in the influential Euro+Med demonstrated that many well known These studies indicate that Aster PlantBase database (Greuter 2003). Chinese species currently in Aster in the old sense was a mixture of Mindful of the impact that the actually represent three new species from all over the world that proposed name changes would have unnamed genera that are closely were not particularly closely related, on a popular group of plants, the related to Australasian species. and really belonged in other smaller RHS Nomenclature and Taxonomy African asters also comprise genera. Reflecting these results in Advisory Group (NATAG) has been several genera. The Madagascan the names of the plants has resulted monitoring the adoption of the new species are referred to Madagaster, in describing new genera, resurrect­ classification by the international Aster comptonii to Afroaster, and ing old genera, and raising infragen­ botanical community over the past Aster capensis and Aster harveyanus eric taxa to generic rank, all of which 10 years. After considering the still await placement. creates unfamiliar new names. evidence and noting the widespread The North American species While this might initially give rise acceptance of the new taxonomy, form a single large grouping that to some inconvenience, it does NATAG has recommended its splits in to many genera, including reflect a more realistic classification. adoption for the 2015 edition of the the horticulturally important Plants that are genuinely similar, as RHS Plant Finder. Cross references Doellingeria, Eurybia and ➤ June 2014 121 nomenclature Symphyotrichum, the last containing There are several more genera to be (1964), Cullen et al. (2000), Picton the majority of Michaelmas daisies. separated out of it, even in Eurasia. (2004) and Shi et al. (2011). South American asters have also The only certainty is that A. amellus been divided up, with several species and its close relatives remain Doellingeria now in Symphyotrichum, and others in permanently in Aster. Helpful This genus of three species from genera such as Diplostephium, accounts of the cultivated and wild eastern North America consists of Noticastrum and Oritrophium. species can be found in Grierson hardy, herbaceous perennials. The Genera in cultivation key to replaCement Aster Genera in Cultivation The new and unfamiliar genera that 1a Plant sprawling or vine­like, shrubby habit Ampelaster carolinianus are most widespread in horticulture 1b Plant herbaceous, annual or perennial, or alpine sub­shrub 2 are discussed below, and their 2a Dwarf alpine herb with fleshy tap root Oreostemma alpigenum distinguishing features are 2b Taller herbaceous plants or alpine subshrubs 3 highlighted. The descriptions are 3a Ray florets absent 4 quite technical as the genera tend to 3b Ray florets present 5 be separated on characters 4a Leaves pubescent, glandular Galatella (Linoseris) associated with the involucral bracts, 4b Leaves hairless, without glands Tripolium pannonicum achene or pappus. The table on p123 shows the new generic placement of 5a Ray florets sterile without styles Galatella 5b Ray florets fertile, 2 styles present 6 currently cultivated asters, along with a reference to a convenient flora 6a Involucral bracts in 2 indistinct rows, all nearly equal Aster where a description can be found. 6b Involucral bracts in 3–5 rows, often very unequal 7 7a Basal and some cauline leaves petiolate, lamina base cordate to subcordate Ampelaster Eurybia This is a genus of a single species, 7b Basal and lower cauline leaves petiolate, lamina base not cordate or A. carolinianus (syn. Aster carolinianus) sometimes sessile 8 from the Florida region forming a 8a Stem with usually 10 or less capitula (flowerheads) 9 large sprawling or vining shrub with 8b Stem with more than 10 capitula (flowerheads) 11 weak stems to 4m long. It is usually 9a Capitula solitary, alpine to 15cm, achenes dimorphic Xanthisma coloradoense evergreen, but deciduous in cooler 9b Capitula several, herbaceous perennial to 70cm or more, achenes uniform 10 areas. The leaves, 3­7 x 1­2cm, are 10a Outer involucral bracts obtuse to rounded; mid to upper stem leaves alternate, thin­textured, with bases narrowed at base Aster amellus and relatives clasping the