Recent name changes in the aster family (Asteraceae)

Recent waves of name changes have produced bewildering sets of technical-sounding Latin for old, once-familiar plants. The huge aster family (Asteraceae) has been especially prone to such change. Many long-recognized genera have been split apart, with new names for segregates and with older, widely known names no longer applied in the same way. Even professional botanists are resistant to changes and have been reluctant to use new systems of names. For the most part, though, recognition of smaller, better-defined groups has proved useful and the new names have been adopted.

Most name changes reflect a better understanding in the evolution of the plants, because most botanists find it consistent to have evolutionary lineages exactly reflected in scientific names and classifications. Increased understanding has resulted from intensive study of the plants themselves (stems, leaves, flowers, fruits) and especially from the recent ability to compare internal structure of DNA molecules. DNA comparisons provide a huge amount of evidence for construction of evolutionary trees, and one of the most common DNA discoveries has been that species long thought to be closely related actually are not. Instead, their similarities have evolved independently. For example, North American asters are more closely related to goldenrods than to native European and Asian asters.

Of course, changing a name changes nothing about the plant itself, and colloquial and horticultural names usually remain exactly the same. But reference to a scientific name opens doors to information about a species and its closest relatives. “Michaelmas Daisy” could refer to any of dozens of species. Aster novi-belgii narrows the concept to a single species. Symphyotrichum novi-belgii is the same species but even more specific in referring to the group of species most closely related to it.

Here are summaries of what’s happened recently with names in Aster, Senecio, Eupatorium, and Chrysanthemum, where radical changes have occurred.

Aster.

The concept of the genus Aster is linked by rules of scientific nomenclature to a single species, Aster amellus, native to Europe and Asia. In a 1994 study of asters world-wide, structure of chromosomes and achenes indicated that Eurasian asters stand apart from North American species. DNA study soon confirmed this and also showed that the North American species are more closely related to Solidago, Erigeron, Boltonia, and many other American genera than to Eurasian species of Aster. The large genus that had been long-recognized as Aster was identified based on unifying concept of little more than a rhizomatous, herbaceous, perennial habit and numerous white to blue rays. It’s clear now that this combination of features occurs in many distinct groups and that the evolution of Eurasian asters occurred independently of the American species.

Even the Eurasian species are not most closely related among themselves.  Aster tripolium (now placed as the single species of the genus Tripolium) is most closely related to the modern genera Crinitaria (Aster linosyris, A. oleifolius, and others) and Galatella (A. punctatus, Aster sedifolius, and others). Some botanists include Crinitaria within Galatella. As a group, these species are most closely related to the currently recognized genera Bellidiastrum (including only the single species Aster bellidiastrum), Bellis, and Bellium. The evolutionary relationship of Aster in the strict sense is closest to Australasian genera. The genus Aster is now limited to A. amellus and about 180 other species, including many beautiful species native to Europe and Asia (e.g., A. ageratoides, A. diplostephioides, A. flaccidus, A. himalaicus, A. tataricus). Among the closest relatives of A. amellus are A. pyrenaeus and A. thomsonii.

Species of the Asian genus Kalimeris (e.g., K. incisa and K. mongolica) are shown by DNA evidence to have evolved among species of Aster in the strict sense, and they already have gone in some classifications to species names within Aster. The Kalimeris species, however, remain distinct as a group, and may continue to be recognized by some botanists as the genus Kalimeris.

The approximately 180 species North American species of Aster are divided among diverse evolutionary lines. The only native North American species that remains in Aster is A. alpinus, ranging from Asia across to Alaska and southward through the Rocky Mountains. By far the largest number of the species transferred from Aster to other genera, including the majority of those cultivated in Europe, are now in Symphyotrichum. Aster ptarmicoides proves to be a white-rayed species of Solidago, where it is closely related to Solidago rigida and S. riddellii.

Commonly cultivated North American Aster segregates (with total numbers of species in each genus)

Symphyotrichum (90) - A. cordifolius, A. dumosus, A. laevis, A. lateriflorus, A. novae-angliae, A. novi-belgii

Eurybia (27) - A. divaricatus, A. macrophyllus

Doellingeria (3) - A. umbellatus

Oreostemma (3) - A. alpigenus

Solidago - A. ptarmicoides

Senecio.

Senecio has been considered to be one of the largest genera in the world, with species of vines, trees, herbs, and shrubs. But plant taxonomists have been at work since the 1970’s, creating many smaller, more uniform genera (sometimes reviving older, little-used names) from within this giant genus. Perhaps because some of these segregate names have been in use for more than three decades, they are more widely used and have become more familiar to gardeners. Even after such concentrated study and reshaping, Senecio in the strict sense (linked to the concept of S. vulgaris) still is recognized to include over 1200 species worldwide, two-thirds of them in South America and Africa, the rest mostly in Europe, Asia, Australia, and North America. Many cultivated species remain as Senecio in the narrow sense.

Commonly cultivated species of Senecio segregates (with total numbers of species in each genus)

Brachyglottis (11) - S. grandifolius, S. hectoris, S. monroi

Kleinia (45) - S. amaniensis, S. articulatus, S. elegans, S. fulgens, S. kleinia, S. stapeliiformis

Ligularia (125+) - S. palmatifidus, S. sibiricus, S. stenocephalus, S. veitchianus

Packera (64) - S. aurea

Pericallis (15) - S. citriformis, S. cruentus

Senecio (1000+) - S. cineraria, S. doronicum, S. ficoides, S. incanus, S. jacobaea, S. pendulus, S. radicans, S. scaposus, S. sylvaticus

Tephroseris (ca. 50) - S. aurantiacus, S. cacaliaster, S. helenitis

Many species of Pseudogynoxys (vines with orange-yellow to reddish florets) and Roldana (yellow-flowered shrubs mostly from Mexico) are beautiful and surely will find their way to cultivation. The well-known genera Euryops and Gynura also are close relatives of Senecio.

Eupatorium.

Eupatorium, like Senecio, was long considered to be a huge genus. Unlike Senecio, though, Eupatorium came to include many species widely unrelated to it (even including species of Vernonia, Baccharis, and Pluchea)––united by a concept based on leaves usually opposite, rays absent, disc florets white to blue or pink (not yellow), and a pappus of capillary bristles. Also unlike Senecio, species of Eupatorium in the broad sense are mostly restricted in native range to the American continents. A small group of species is native to eastern Asia, its ancestors arriving there through migration from North America.

Beginning in the late 1960’s, when Eupatorium was considered to be a genus of 2300 species, botanists from the Smithsonian Institution were able to discover many species clusters and began to separate out smaller, more uniform groups. By 1989 they had described anew or reinstated 105 additional genera from within the genus, and Eupatorium in the narrow sense (linked to the concept of E. cannabinum) became a genus of only about 40 species. DNA evidence has supported many of the new segregates, although many problems remain and much reseach is underway.

Examples of commonly cultivated species of Eupatorium (with total numbers of species in each genus)

Ageratina (250) - E. aromaticum, E. ligustrinum, E. rugosum

Bartlettina (35) - E. atrorubens

Conoclinium (4) - E. coelestinum

Eutrochium (5) - E. purpureum, E. maculatum, the spectacular joe-pye weeds

Fleischmannia (80) - E. incarnatum

Mikania (450) - E. scandens

Many beautiful species have yet to be cultivated.

Chrysanthemum.

For almost 250 years, Chrysanthemum was a genus of about 200 species, including mums and florists’ chrysanthemums, marguerites, Paris daisies, Shasta daisies, and others. In 1993 European botanists were able to arrange the species of the Chrysanthemum complex into a number of distinct groups, recognizing each of the groups as a separate genus and providing each with a name. In this new system of more narrowly defined names, the florists’ chrysanthemum (Chrysanthemum indicum) was linked to the concept of the genus Dendranthema, and so, according to nomenclatural rules, Dendranthema became the correct name for what had long been known as Chrysanthemum (though in a much narrower sense than previously). Correct names for mums were Dendranthema indicum, D. japonicum, D. xgrandiflorum, etc.

So intense and general was the dislike of this solution for Chrysanthemum names that in 1999, by vote of an official international nomenclatural rules committee, the concept of the genus Chrysanthemum was formally linked to C. indicum, so that the generic name would refer to florists’ chrysanthemums. Even so, the narrower view of genera has prevailed and many species are still distributed among genera with relatively new and unfamiliar names. Most of the cultivated species now are in these genera of the Chrysanthemum complex.

Commonly cultivated species of the Chrysanthemum complex segregates (with total numbers of species in each genus)

Arctanthemum (arctic chrysanthemum, 1 species) - C. arcticum

Argyranthemum (marguerites and Paris daisies, 23 species) - C. anethifolium, C. foeniculaceum, C. frutescens

Chrysanthemum (florists’ mums, ca. 40 species) - C. xgrandiflorum, C. indicum, C. japonicum

Glebionis (corn chrysanthemums and crown daisies, 3 species) - C. segetum, C. coronarium

Heteranthemis (sticky ox-eye daisy, 1 species) - C. viscidehirtum

Ismelia (tricolor chrysanthemum, 1 species) - C. carinatum = C. tricolor

Leucanthemella (high-daisy, giant-daisy, 2 species) - C. serotinum

Leucanthemopsis (alpine marguerites, 6 species) - C. alpinum, C. pallidum

Leucanthemum (ox-eye daisy and Shasta daisies, ca. 26 species) - C. leucanthemum, C. maximum, C. lacustre, C. xsuperbum

Rhodanthemum (Moroccan daisies, 12 species) - C. hosmariense, C. gayanum, C. atlanticum).