Flora Pittsburghensis

Bohemian Knotweed (Fallopia x bohemica)

Photographed September 9.

Father Pitt is about to make a botanical pronouncement that is likely to be controversial, and even likely to be wrong. He believes that most of the “Japanese knotweed” that has become such a plague around Pittsburgh is actually Bohemian Knotweed, a hybrid between Fallopia japonica and Fallopia sachalinensis. He has two mean reasons:

1. The leaves are usually intermediate between F. japonica and F. sachalinensis, with bases that are not quite heart-shaped like the leaves of F. sachalinensis, but more shovel-like than the leaves of F. japonica.

2. The rapid spread of the weed can only be accounted for by seed dispersal, and reliable authorities tell us that the hybrid is much more likely to produce viable seeds than either of its parents. Thus, once the hybrid gains a foothold in the area, it is likely to become the most common of the three in a very short time.

If any botanists out there can help him verify or correct this identification, Father Pitt would be very grateful.

These plants were growing along a street in Beechview, where shady woods did not discourage them at all.

Taxonomically the Japanese monster knotweeds are in a mess. The Flora of North America puts them in Fallopia. Wikipedia, following many current botanists, places them in Reynoutria, explaining, “As with many species in the family Polygonaceae, the taxonomic boundaries of Reynoutria have been much confused; in particular, it has been repeatedly merged with and separated from Fallopia.” The USDA PLANTS Database lumps everything together in the giant genus Polygonum. Father Pitt had to pick one of those possibilities almost at random.
Moss Rose (Portulaca grandiflora)

Photographed September 8.

One of the garden favorites that have become occasional urban weeds, Moss Rose can pop up just about anywhere. This one was growing out of the asphalt along the curb on a back street in Brookline. We can see its family resemblance to the much more common Purslane (Portulaca oleracea): both are succulent plants, mostly flopped along the ground (“prostrate,” as the botanists would say), with five-petaled flowers. But the flowers of P. grandiflora are, as the name implies, very large in proportion to the rest of the plant, and they come in many colors; volunteers are most commonly electric magenta like this one. The leaves of P. grandiflora are more linear, as opposed to the elliptical leaves of P. oleracea.
Sneezeweed (Helenium autumnale)

Photographed August 26.

We last looked at Helenium autumnale in 2015. Since then it has become very well established in that meadow in Schenley Park. We repeat the text of the earlier article:

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; this one was growing in Schenley Park, in a section of former lawn that is being allowed to grow into a meadow for better water retention. It was blooming in the middle of September.

Gray describes the genus and the species:

HELÈNIUM L. SNEEZEWEED. Heads many-flowered, radiate; rays several, wedge-shaped, 3-6-cleft, fertile, rarely sterile. Involucre small, reflexed; the bracts linear or awl-shaped. Receptacle globose or ellipsoid. Achenes top-shaped, ribbed; pappus of 6-8 thin 1-nerved chaffy scales, the nerve usually extended into a bristle or point. — Erect branching herbs with alternate leaves, often sprinkled with bitter aromatic resinous globules; heads yellow, rarely purple, terminal, single or corymbed. (The Greek name of some plant, said to be named after Helenus, son of Priam.)

Leaves broad, decurrent on the angled stem.

H. autumnàle L. Perennial, nearly smooth, 0.2-2 m. high; leaves mostly toothed, lanceolate to ovate-oblong; heads larger (2-4 cm. broad); disk yellow; rays fertile, yellow. — Alluvial river-banks and wet ground, w. Que. and w. Mass. to Man., southw. and westw. Aug.-Oct.
Morning Glory (Ipomoea purpurea), Pale Blue Form

Photographed September 2.

Morning Glories are very common weeds here; they can be quite rampant, but they reward us with gorgeous flowers. By far the majority are in deep purple or pink, but the genetics of the species are variable enough to have produced a wide variety of cultivated colors, and we sometimes see unusual colors in the wild. Here is a wild pale-blue form that grew in Beechview.
Wild Senna (Senna hebecarpa)

Photographed August 26.

A tall and showy plant found at the edges of woodlands and in meadows; these were growing in a meadow in Schenley Park. The flowers are golden yellow with black-headed stamens, and they are delicious to bumblebees.

Until the 1930s this was apparently regarded as a stout form of the generally smaller and more delicate Senna marilandica.

Bohemian Knotweed (Fallopia x bohemica)

Moss Rose (Portulaca grandiflora)

Sneezeweed (Helenium autumnale)

Morning Glory (Ipomoea purpurea), Pale Blue Form

Wild Senna (Senna hebecarpa)