All asters look identical. They all bloom in the fall. Only a fanatic could tell them apart!
None of the above statements are true, but sometimes it sure seems that way. All asters aren’t even members of the same genus, not any more anyway. They include members of Doellingeria, Eurybia, Ionactis, Oclemena, Sericocarpus, and Symphyotrichum. There are many more flowers that might reasonably be mistaken for asters, among them the fleabanes (Erigeron).
About the only thing all asters have in common is that they are composite flowers, composed of ray flowers (petals) and a central disc comprised of tiny disc flowers.
Wild aster flowers are most often white or blue, but they grade from white to blue to deep purple and occasionally pink. Yellow centers are most common, but some flower centers are variously colored; to further confuse matters, they darken with age. The number of ray flowers is an identifier. Flowers may be sparse or dense, appearing along the stems in racemes or in clusters on top (panicles). Leaf structure varies greatly and is often a key identifying feature. Most asters do bloom in the fall—along with goldenrods, they make up most of the wildflowers visible in temperate regions at this time of year.
Symphyotrichum on www.wildflowers-and-weeds.com
Symphyotrichum on Ontario Wildflowers
Symphyotrichum on Wikipedia
Symphyotrichum on gardeninacity.wordpress.com
Symphyotrichum on fieldbioinohio.blogspot.com
Symphyotrichum on eFloras
The table below compares some among many similar-appearing asters. See also fleabanes, which look similar but have more ray flowers. The aster family is enormous, over 23,000 species, and we are only concerned here with a group that are commonly called asters, and some similar-appearing relatives. See also Arieh Tel’s well-researched and informative aster comparison guide.
Doellingeria umbellata var. umbellata
|Plant||Plants form dense, bushlike clusters up to 5' (1.5 m) in height.||Plants are 20-79" (50-200 cm) high. Stems are green, sometimes purple or yellowish-brown.||Plants are 4-35" (10-90 cm) tall, with stiff stems and sticky hairs, often branching toward the top.|
|Flowers||Each flower is a composite flower, composed of a central yellow disc with 230-400 tiny disc florets, surrounded by 45-60 white or pale purple rays. Flowers are up to 1¾" (5 cm) across, occurring in dense panicles or corymbs. They appear from August to September.||corymb. Individual flowers are up to 1½" (3.8 cm) across, with 15-35 blue to purple rays and 25-55 tiny flowers in the central disc.|
|Leaves||Leaves decrease in width until they form wings on their stems (“decurrent”). They are up to 6" (15 cm) long, and linear or lanceolate.||elliptic or lanceolate-elliptic. They have prominent veins, and pale or whitish green undersides.||Alternate, unlobed, mostly toothless, rough or hairless, and ⅜-6" (1-16 cm) × ⅛-1½" (3-40 mm). Their shapes are lanceolate or elliptic to ovate- or obovate-elliptic or spatulate. This translates roughly to rounded or spoon-shaped. Leaves may be attached directly to the stem (sessile), or on short winged petioles.|
USDA Zones: 4-8
|Habitats||Moist thickets, meadows, swamp edges||Dry, sandy woods and clearings, especially in coastal pine barrens.|
Solitary or in panicles. Flowers are ½-1" (1.3-2.5 cm) across, with 10-20 rays that are lavendar-colored, and yellow central disks that become red-brown with age. They appear Aug-Oct.
In a roughly spherical cluster at the top, of flowers that are ⅞-1½" (2.5-4 cm) in diameter. Flowers are composed of disheveled-looking white ray flowers surrounding a central disc that is yellow or purplish in color. Ray flowers are bent backward, not straight as in most other aster family flowers, and composed of about 15 (9-18) rays.
Flowerheads are panicles, roughly cone-shaped. Individual flowers are ½-¾" (1.5-1.9 cm) across, with 8-20 (usually 10-16) blue to blue-purple ray petals. Sometimes they are pale, almost white. Central disc flowers are yellow, reddening with age. They appear from Aug to Nov.
Alternate leaves are ¾-1½" (1.9-3.8 cm) × ⅛" (3.2 mm), shiny, sessile, linear, and pointed, like spruce needles. They lack teeth, but leaf edges are rough.
Oval, coarsely toothed, pointed leaves form a whorl around the stem. The arrangement of leaves resembles a pinwheel when viewed from above.
Alternate, on petioles (stalks). 1½-6" (3.8-15 cm) long, heart-shaped with deeply cleft bases, pointed, sharply toothed, rough on top, hairy on the underside.
USDA Zones: 3-8
Blooms appear from Aug to Oct. There are many flowers, but each tips a separate branch with its own leaflets and they are spread along branches, not clustered at major branch ends. The flowers therefore look evenly distributed, not densely clustered as in most asters. Individual flowers are white or pale blue/purple, ½-¾" (1.3-1.9 cm) in diameter, with 13-30 rays. Central disks are yellow, reddening with age.
Bluish to purple (rarely white), ¾-1¼" (1.9-3.2 cm) across, appearing from August to October. Central disc flowers are yellow, aging to purple. There are 13-23 (rarely up to 11-34) rays on each flower. The appear in loose panicles.
Flowerheads are panicles that may be heavily branched and densely or quite sparsely flowered. Flowers are white to pinkish or pale blue-violet, ⅜-¾" (1-2 cm) across, with 16-50 rays and usually 20-40 tiny disc florets. Central disks are yellow, aging to purple.
Smooth, bluish in color, thick and firm, usually toothless, usually hairless, and clasping.
Leaves are ⅜-3" (1-8 cm) × ⅛-¾" (5-20 mm), with serrated or scalloped edges, oblanceolate or lanceolate. Dead leaves tend to curl a lot.
USDA Zones: 3-8
In dense, highly branched clusters atop the plants. Each flower is ¾-1½" (1.9-3.8 cm) around, with a yellow-orange disk flower in the center, surrounded by 45-100 thin ray flowers that are deep, vibrant purple, pale purple, or pink. They flower from Aug to Sep.
The central disc has 28-68 tiny florets and is yellow, aging to reddish brown or purple. Flowers have 15-35 rays that are bluish to purple, rarely pink or white, are about 1-1¼" (2.5-3.2 cm) in diameter, and appear from Aug to Oct. New York aster tends to be paler in color than New England aster.
Alternate, hairy, spatula-shaped, lanceolate or oblong, with their bases slightly wrapped around the stem (“clasping”). They are usually smooth, but may have shallow teeth, and are ¾-3" (2-8 cm) × ⅛-⅞" (5-25 mm).
Thick, unlobed, ovate to lanceolate, sessile (attached directly to stems) or clasping, ⅝-2" (1.7-6 cm) × ⅛-⅜" (6-11 mm). Leaves near the bottom are already drying out and falling by flowering time, while those higher on the stem remain, becoming smaller further up. Leaves sometimes have teeth.
USDA Zones: 4-8
USDA Zones: 3-8
Openly branched panicles. Individual flowers are ⅞-1½" (2.5-3.8 cm) across, and pale to dark blue-purple, sometimes almost white, with 20-50 rays. Central discs are yellow or cream-colored, with 30-50 tiny florets (as many as 90), aging to pink or purple. They appear Aug-Nov.
Numerous flowers are clustered along long stems in racemes. The central disk is yellowish, aging to a pinkish color. Ray flowers are white to pink, with 16-20 rays, rarely as few as 12. Flowers are about ½" (1.3 cm) across, and they tend to cluster along one side of each branch. They appear from August to October.
Oblanceolate, with small teeth that are usually widely spaced and may not be present, and bases that clasp the stems. They are up to 6" (15 cm) long and 2½" (7.0 cm) wide, with an easily visible central vein.
Alternate, sometimes toothed, unlobed, ⅛-1½" (5-40 mm) × ⅛-½" (5-15 mm) in size.
USDA Zones: 2-9
Symphyotrichum description by Thomas H. Kent, last updated 12 Oct 2018.