Flora Pittsburghensis.

Compositae or Asteraceae.

Composite, Daisy, or Aster Family.

Tall Ironweed (Vernonia gigantea). No photograph can convey the vivid purple color of ironweed, one of our most spectacular late-summer flowers. A field of mixed ironweed and goldenrod is a sight not easily forgotten. Two species are common in our area, and they hybridize; Tall Ironweed is, as its name implies, taller than New York Ironweed (Vernonia noveboracensis), but otherwise very similar.

Tall Thoroughwort (Eupatorium altissimum). Long stands of this dusty white thoroughwort line our highways. The narrow grey-green three-ribbed leaves (sometimes there are five ribs) are distinctive, and the mounds of white flowers are very attractive to honeybees.

White Snakeroot (Ageratina altissima). One of our most decorative late-summer and autumn flowers, White Snakeroot lights up the edge of the woods and can form a perfect ornamental border around a field. The flowers are pure white, with projecting white stamens, As a member of the Composite family, this species is especially interesting for the way the individual little five-parted flowers are easily distinguishable in the heads. It’s a good plant for demonstrating the construction of a Composite flower to children.

Wreath Goldenrod (Solidago caesia). A more contemplative sort of goldenrod. Its showier cousins brighten fields and meadows, but the Wreath or Blue-Stemmed Goldenrod is happiest in an open woodland, thriving in deeper shade than almost any other other fall flower. Its arched stems of golden flowers have a restrained elegance that seems appropriate to the dim religious light of the woods.

Zigzag Goldenrod (Solidago flexicaulis). A distinctive goldenrod that likes clearings in the woods or the banks of a stream. Its broad rounded toothy leaves are distinctive, and it takes its common name from the angled stems, which zigzag from one leaf to the next. (“Zigzag” is a technical term in botany.) The flowers grow in a wand at the top of the stem, with more flowers filling in the leaf axils.


Fleabane (Erigeron annuus). A very common but always delightful weed; its multiple heads of cheery daisy-like flowers bear large numbers of delicate white rays. It can be found on roadsides, at the edges of parking lots, in vacant lots, or in lawns given half a chance. Its peak blooming season is in June.






Elecampane (Inula helenium). Elecampane is a tall and striking flower, imported from Europe, recognizable by its thick stems of sunflower-like flower heads with narrow, shaggy rays. It is not particularly common around here, but abundant where it does take up residence.


Ragweed (Ambrosia artemisiifolia). The bane of allergy-sufferers everywhere, Common Ragweed is wind-pollinated: instead of large attractive flower heads, it relies on myriad small pollen-dispensers. The plant in full bloom passes nearly unnoticed, even in large drifts. It grows everywhere—in cracks in the pavement, in vacant lots, at the edge of a yard, in the middle of your garden.

Giant Ragweed (Ambrosia trifida). A heaping helping of ragweed, easily growing to 9 feet (3 m) if it likes the location (Gray says to 6 m or 18 feet), and letting loose a raging torrent of allergenic pollen in early September. The harmless and beautiful goldenrods that bloom at the same time often take the blame for hay fever, but this huge yet somehow inconspicuous weed, and its even more common little cousin A. artemisiifolia, are the real culprits.







Wingstem (Verbesina alternifolia). A tall and cheerful native flower that may be abundant in some areas and absent in others. It likes the edge of the woods, and seems to be happiest on a hillside. The disk florets are unusually large, arranged pincushion-fashion. The drooping rays are irregular and rather sloppy; there may be only two of them, or up to eight, and they be be significantly different in size and shape.


Spanish Needles (Bidens bipinnata). This is one of those flowers that reward a close look. The flowers are like tiny marigolds, and indeed they’re sometimes called bur-marigolds. The seeds, long and narrow like marigold seeds, have hooks that stick in animal fur or people’s clothes.

Pittsburgh Pest (Galinsoga parviflora). Obviously this is not known as Pittsburgh Pest everywhere in its nearly global range, but the name seems to be well established here, and it is frequently used elsewhere in the United States. The flowers are like tiny five-rayed daisies; the plant is low and hairy, and can grow from any crack in the pavement. It is very much an urban weed, ubiquitous in the city of Pittsburgh, but much rarer in the near suburbs, and unknown in all the other counties of the metropolitan area but one (Washington County).

Sneezeweed (Helenium autumnale). Sneezeweed is an attractive composite flower with distinctively notched rays that make it easy to identify. (A similar species, Purple-Headed Sneezeweed, Helenium flexuosum, has been introduced in a few locations; it is easy to distinguish by the dark brownish button in the center.) The plant likes damp areas.

Yarrow (Achillea millefolium). Also called Milfoil, “thousand-leaf,” from the finely divided leaves. A European import that has become a common wildflower all over the East. Still a popular garden flower; in recent years many colors have been bred, but the wild ones are almost always white, or more rarely pink. The blooming season is long, from June through October.


Ox-Eye Daisy (Leucanthemum vulgare). Considered a noxious weed in some parts, but around here it seldom takes over enthusiastically enough to be a problem. This is the flower commonly known as “daisy” to Americans, and it is more beloved than hated almost everywhere it grows. It holds its daisies up proudly on long stems perfect for cutting. In most of our older references, this species is placed in the genus Chrysanthemum.

Tansy (Tanacetum vulgare). A rayless Composite: that is, a flower head with only disc flowers and no rays, like a daisy with no “petals.” The yellow button-like discs and lacy fernlike foliage are distinctive. Tansy came over here as a garden staple, but it has made itself at home. It is never abundant enough in Pittsburgh to qualify as a pest; it is only a pleasant visitor popping up in unexpected places.


Coltsfoot (Tussilago farfara). Coltsfoot is one of our earlier spring flowers. The cheery and shaggy yellow flower heads top a short stalk that pops straight out of the ground; there are no leaves until later on. The plant’s favorite habitat seems to be a damp hillside at the edge of the woods, often beside a street or highway. Coltsfoot was, as its generic name suggests, a popular cough remedy; but it has been known to cause serious liver damage, so it’s not as popular as it used to be.



Groundsel (Senecio vulgaris). This ubiquitous weed is found in temperate latitudes throughout the world. The tight little flower heads never open up any wider than what you see here. This plant has one of the longest blooming seasons of all our weeds: on this page we have pictures from late June and from early February.


Bull Thistle (Cirsium vulgare). This is the big, spiny thistle that always pops up just where you don’t want a thistle. On the other hand, goldfinches love the seeds so much that it’s hard to imagine how the birds survived before Europeans introduced the plant to this continent. Architecturally, the whole plant is very elegant, and the flower heads are superbly artistic, with a tuft of pure magenta erupting from a prickly urn. The flowers begin in July and continue on and off till frost.


Chicory (Cichorium intybus). The distinctive sky-blue flowers make Chicory unmistakable. Varieties of Chicory are used as salad greens and as a coffee substitute or additive. It grows along roadsides, often in the company of Queen Anne’s Lace (Daucus carota), and seems especially happy in a crack in the asphalt at the edge of a parking lot.




Dandelion (Taraxacum officinale). Dandelions can bloom almost any time of the year; they prefer the cool weather of spring, but will bloom sporadically through the summer, with another burst of enthusiasm in the fall, and occasional appearances even in the winter if we have a warm spell. No matter how much suburbanites hate dandelions in their lawns, anyone with any aesthetic sense must grudgingly admit that the common dandelion is one of our most perfectly beautiful flowers.