Asters of the Ottawa region
Curator Emeritus, Botany Division, Canadian Museum of Nature
My objective in presenting this series of articles on various plant groups of this region is to try to explain how to identify them in the simplest way possible without recourse to the technical words usually associated with systematic botany. This is not always possible because technical jargon is designed to be precise and concise, an attribute difficult to assign to common English.
I believe this objective is feasible because of the nature of floras. It is evident
that it is easier to identify the lower number of species to be found in a smaller
area as opposed to the larger number in a larger area. For example. Gray's
Manual, which covers all of eastern continental USA and eastern Canada, contains a key to 67 species of Aster, Semple and Heard's treatment of the Asters
of Ontario contains 32 species. In the Ottawa-Hull region we have only 14
species. Therefore, it should be easier to separate these on gross characteristics
rather than to resort to the use of more technical characteristics that are difficult to discern. This ideal may be feasible for the more easily separated
species, but is not always possible for the separation of very similar species.
Unfortunately we have a couple of these here.
Outside of the gaudy introduced Purple Loosestrife which fills our fields and
wetlands and blooms in August, the goldenrods and the asters or Michaelmas
Daisies are among the more showy native flowers to be found in this region.
The goldenrods we covered in an earlier article (Gillett 1991). The number of
Aster species (14) is the same as for the goldenrods. The scientific name for the
genus is the same as the English name so it is very easy to remember. It should
not be confused with the "Aster" of our cultivated gardens which is really the
China Aster, Callistephiis chinensis Nees, an annual from China and Japan,
which appears in many colours excepting yellow.
Both asters and goldenrods are members of the family Asteraceae (alternate
name Compositae, i.e., if you don't like the name Asteraceae, then you can use
Compositae), characterized by flowers borne in heads, as in the daisy (Chrysanthemum). Each head is composed of tubular disc flowers (yellow) in the central
portion and usually, but not always, is surrounded on the outside with flowers
having flat strap-shaped ligulate flowers, the ray flowers to which we usually
ascribe the flower's colour. The whole group of flowers is enclosed in a ring or
involucre of green bracts (called phyllaries). This arrangement of flowers
constitutes a very efficient pollination method because the head of flowers acts
collectively like a single flower. The insect pollinator then is provided with a
landing platform and is able to visit many flowers at the same time. Thus the
arrangement works both ways; the insect obtains more pollen or nectar with
less effort and more flowers are pollinated by the insect.
Aster ptarmicoides (Nees) T. & G., the Upland White Aster [Aster Faux-ptarmica] which appears on my checklist of Ottawa District plants (Gillett and
White 1978) is now (Gillett 1991) included among the goldenrods as Solidago
ptarmicoides (Nees) Boivin, so you see it is not always easy to tell a goldenrod
from an aster!
Taxonomically the genus Aster is considered to be quite difficult. One of the
problems is to settle on borders for the genus; another is the recognition of
certain species. When the genus is studied over its entire range, there are
problems distinguishing some species from members of the genera Baccharis
or Vemonia which, fortunately for us, do not occur in this area. We do, however, have a couple of difficult-to-distinguish species.
Key to the asters of the Ottawa-Hull region
The 14 species of Aster that occur here can be keyed out as follows:
At least the lower leaves cordate (heart-shaped) or rounded at the base and
with obvious petioles (stalks).
Go to 2
Leaves not cordate and not always with petioles.
Go to 4
Inflorescence usually forming a corymb, i.e., the lower flower stalks are longer
than the upper so the entire flower cluster is more or less flat on top (as in
illustration of A. umbellatus); inflorescence branches glandular and with broad,
almost leafy, firm bracts (these are the bracts on the inflorescence stalks not
those surrounding the flower head which are called phyllaries). Flowers violet
or lavender. Aster macrophyllus
Inflorescence elongate, forming a panicle (a loosely branched compound
flower head); inflorescence branches not glandular and with narrow,
numerous, small bracts.
Go to 3
- Leaf petioles without wings; inflorescence often with more than 100 heads.
Flowers blue violet to pink.
Leaf petioles distinctly winged; inflorescence usually with less than 50 heads.
Flowers blue or violet.
Either the involucral bracts (phyllaries), or even the seeds, distinctly glandular, sometimes the rest of the plant as well. To see this you are going to need the 10× lens that I suggested you buy in an earlier article
Go to 5
Plants not glandular
Go to 7
Leaves strongly clasping at the base. Flowers dark purple to pink or white
Leaves tapered, not clasping at the base
Go to 6
Leaves 2-6 cm wide, with prominent teeth, long slender tips and forming
apparent whorls due to shortening of the stem nodes; 10 to 20 leaves below the
inflorescence. Flowers white to faintly pinkish
Leaves linear-lanceolate, 0.5 to 1.2 cm wide, without teeth; 25-40 leaves below
the inflorescence. Flowers pink or lilac-purple
Leaves clasping at the base. Flowers pale mauve to dark purple or white
Leaves not at all or scarcely clasping
Go to 8
Annuals with the ray flowers shorter than the mature pappus. (The pappus is a
cluster of hairs found on the tip of the seed or achene in Asteraceae). In this
species the pappus is visible at any stage because of its abundance and length
Perennials with long well-developed ray flowers longer than the mature
Go to 9
Flowers with white rays borne in a somewhat flat-topped corymb; plants up to
2 m tall, often forming dense stands; in marshy areas
Smaller plants with flower heads forming a more elongate inflorescence; plants
not in marshy areas
Go to 10
Flower heads usually on a simple raceme (unbranched pedicels for each flower
head); heads 2.0 to 2.5 cm wide, purple or white
Heads smaller, borne in obvious panicles (with branched pedicels)
Go to 11
Heads very numerous, often borne on one side of the branches; leaves extremely numerous and narrow, about 1 cm long and 0.1 to 0.2 cm wide, spine
tipped, (as are the involucral bracts); ray flowers white
Heads fewer, not borne on one side of the branches; leaves fewer, larger,
averaging 10 cm long and about 1 cm wide; neither leaves nor involucral bracts
spine-tipped; ray flowers white to pink
Go to 12
You may not want to go any further with this key as the next two species
A. lanceolatus and A. lateriflorus are considered by Semple and Brammall
(1982) to be able to hybridize. Probably A. ontarionis is a product of this
hybridization. In other words, these three species are not clearly separable
and are only recognizable by a combination of characteristics rather than
any single character. However, I have included the obvious "eye-ball" characteristics. There are others using differences in the disc flowers which are
difficult to express here.
Principle stem leaves 8 to 15 cm long, 0.3 to 0.4 cm wide, lanceolate to linear,
tapering at both ends, nearly clasping at the base, glabrous below (without
hairs), but with fine hairs along the margins; plants forming colonies by extensive underground stems or rhizomes
Principle stem leaves wider than 0.5 cm near the centre
Go to 13
Leaves generally hairy below over the surface; plants with creeping rhizomes;
inflorescence usually elongate; rays white to occasionally pink
Leaves hairy only along the midrib; plants without creeping rhizomes; inflorescence may be elongate also or it may be more ovate; rays white
These last two species are superficially almost identical. In order to distinguish
them you must use that hand lens. The creeping rhizomes are rarely seen on
herbarium specimens. The leaf pubescence is a fairly good character. Aster
ontarionis has short, rough, (scabrous) hairs between the veins and longer hairs
on the central vein, but Semple and Brammall indicate that the leaves could be
quite glabrous! The ray of flowers are definitely shorter in A. ontarionis than in
A. lateriflorus, and both may turn purplish with age.
Notes on individual species
Aster acuminatus Michx.
Whorled Wood Aster
In Gatineau Park and Albert Dugal found it in the Leitrim wetlands. It is primarily an eastern plant found throughout the Maritimes but occurs throughout
southern and eastern Ontario in woods. The ray flowers are white to faintly
pinkish. Whorled Wood Aster is, as the name implies, a woodland species.
Flowering is from August to October.
[photos of Aster acuminatus]
Aster borealis (Torr. & Gray) Prov. (syn. A. junciformis Rydb.)
Found in wet places such as bogs, fens and marshes but has
been found on limestone pavements. I have seen it as far north as James Bay
but it extends right across Canada. Ray flowers are violet or white and bloom
from July to September.
[photos of Aster borealis]
Aster brachyactis Blake
Aster à courts rayons
sandy or gravelly disturbed ground. It seems to be abundant in the Mer Bleue
area on the dry ridge. Dried herbarium specimens show no sign of the short ray
flowers but have clumps of somewhat silvery pappus subtended by tapered
strap-like green involucral bracts. This blooms in September and October.
Aster ciliolatus Lindl.
One of our most
abundant and beautiful fall wildflowers found in fields, in woods, on slopes
and along roadsides. It is easily distinguished from the equally handsome
A. cordifolius by the winged leaf petioles. Ray flowers are blue or violet and
blooming is from August to October.
[photos of Aster ciliolatus]
Aster cordifolius L,
Aster à feuilles cordées
lacks the winged leaf petioles; the heart-shaped leaves alone are not always
enough to distinguish this species from A. ciliolatus. Common at the edge of woods
and in thickets, along river banks. Flowers blue or violet and bloom from July
Aster ericoides L. (syn. Virgulus ericoides (L.) Reveal & Keener)
Not overly common in our area. I have seen it in the eastern
part of Ottawa and it is known from Burritt's Rapids, North Gower and
Prospect. This aster is easily recognized by the numerous small bract-like
leaves. It is found in pastures, along roadsides and in dry meadows. Flowers are
white and bloom from August until October.
Aster lanceolatus (syn. A. simplex Willd., A. paniculatus Lam.)
Aster à feuilles lanceolée
This plant occurs throughout Ontario and is abundant in this district. It is found in open fields and ditches, alvars, dry or moist
meadows. The white flowers bloom from August to early October.
[photos of Aster lanceolatus]
Aster lateriflorus (L.) Britt.
Common in fields,
edges of woods, river banks, rocky shores, alvars, and cedar swamps. The white
flowers bloom from August until October.
This is found in woods, in
thickets, rock outcrops, and alvars. Often you will find large colonies of leaves
without flowering stalks. The lilac-tinged ray flowers will only occur at intervals
but the leaves are distinctive. It blooms from August until October.
[photos of Aster macrophyllus]
Aster nemoralis Ait.
Aster des bois
As the name implies, Bog Aster is
restricted to acidic bogs. Semple and Heard (1987) indicated that the species is
found in the Algoma Highlands and Algonquin Highlands of Ontario. In our
area the Bog Aster is found in bogs in Gatineau Park. Flowers are pink or lilac-purple and bloom from July to September.
Aster novae-angliae (syn. Virgulus novae-angliae (L.) Reveal & Keener)
New England Aster or Michaelmas Daisy
Aster de la Nouvelle-Angleterre
is considerable variation in flower colour in this species, ranging from dark
purple to pink or white. Some have been given cultivar names. New England
Aster is common in fields throughout the region. I have transplanted a few
plants to my garden which were rescued from housing developments. These
asters blend well with my cultivated plants, forming a tall backdrop to the
flower beds. Flowering is from August to October.
[photos of Aster novae-angliae]
Aster ontarionis Wieg.
This species is listed
among our rare plants of Ontario. Habitats include river banks, swamps, rocky
ridges, sandy fields and roadsides. Flowers are usually white but may be pink,
and blooming is from August until October.
Aster puniceus L.
Purple-stemmed aster, Pitnagen, Teaflower
This is a species of swamps, wet cedar woods, along streams and river banks.
Flower colour is extremely variable, from pale mauve to dark purple or white.
This is a very handsome species, flowering from August to October.
Aster umbellatus Mill.
Flat-topped white aster or Umbellate aster
Aster à ombelles
A common species of bogs, wet places, swamps, and depressions in fields. Ray
flowers are white. Flowering is from August to October.
[photos of Aster umbellatus]
There is a possibility that one other Aster occurs in this region. This is
A. oolentangiensis Riddell. It has been collected in Lanark County, Pakenham
Township and has been reported from near Arnprior, and also reported, but
not confirmed, from the talus slopes of the quarry near Lapierre Avenue,
Ottawa. In the key presented here, this species would be among the heart-shaped leaf group of A. ciliolatus and A. cordifolius. The quarry site has a number of native species on the top, such as Symphoricarpos, and since originally a
number of alvars existed there, a common habitat for A. oolentangiensis, it is
possible that it survives man's destructive activities. It is mostly a southern Ontario species and was formerly known as A. azureus. Due to application of the
rules of priority this name had to be changed. Distinguishing characters include
the blue flowers and leaves which are entire (not toothed) or undulate (wavy
margins) and the leaf blades are ovate-lanceolate to oblong, only slightly cordate at the base.
There is one point that I should like to emphasize. A number of native plant
species have great horticultural potential. As I have already mentioned, I
transplanted Aster novae-angliae into my garden. But many of the goldenrods
would also enhance the garden. I have not tried them yet but intend to do so
(I'll check for new housing developments!). Native plants tend to make themselves at home and can often spread more than is desirable. A little careful
weeding will take care of this problem.
As in my previous articles the drawings are by Sally Gadd done many years ago
for my Gatineau Park Flora (unpublished). Because this article covers a larger
area and includes additional habitats, four more drawings by Marcel Jomphe
- Gillett, John M. 1991. Goldenrods. Trail & Landscape 25(4): 114-121.
- Gillett, John M. and David J. White. 1978. Checklist of vascular plants of the Ottawa-Hull region, Canada/Liste des plantes vasculaires de la région d'Ottawa-Hull, Canada. 155 pp. + map.
- Semple, John C. and Ronald A. Brammall. 1982. Wild Aster lanceolatus × lateriflorus hybrids in Ontario and comments on the origin of A. ontarionis (Compositae: Astereae). Can J Bot 60: 1895-1906.
- Semple, John C. and Stephen B. Heard. 1987. The asters of Ontario: Aster L. and virugulus Raf. (Compositae: Astereae). University of Waterloo Biology Series 30. 88 pp.