Wild Flowers of Pittsburgh

Polygonaceae

Oriental Lady’s-Thumb (Polygonum cespitosum)

It is not easy to sort out the taxonomy of this humble weed; we are going by the listing in the USDA PLANTS database, but the species name is also spelled caespitosum (Classical Latin rather than Medieval Latin), and a whole group of related Polygonum species is often separated into the genus Persicaria, in which case this becomes Persicaria posumbu. It is one of several similar smartweeds that frequently pop up in urban areas. This one is distinguished by its dense spike of tiny pink flowers and pointed leaves without markings; the similar Lady’s Thumb (Polygonum persicaria or Persicaria maculosa) has a dark thumbprint mark on each leaf. Look also for tufts of hairs at the stem joints. These plants were growing by a fence in Beechview, where they were blooming in the middle of July.

Gray describes the genus Polygonum and the section Persicaria. He does not describe this species, because it seems to be a twentieth-century introduction; but the description we have given above should distinguish it from the other members of its genus that grow around here.

POLYGONUM [Tourn ] L. KNOTWEED. Calyx 4-6 (mostly 6)-parted; the divisions often petal-like, all erect in fruit, withering or persistent. Stamens 3-9. Styles or stigmas 2 or 3; achene accordingly lenticular or 3-angular. Embryo placed in a groove on the outside of the albumen and curved halfway around it; the radicle and usually the cotyledons slender. Pedicels jointed. — Ours all herbaceous, with fibrous roots (except in P. viviparum), flowering through late summer and early autumn. (Name composed of poly-, many, and gony, knee, from the numerous joints.)

PERSICARIA [Tourn.] L. Flowers in dense spikes, with small scarious bracts; leaves not jointed on the petiole; sheaths cylindrical, truncate, entire, naked or ciliate-fringed or margined; calyx colored, 6-parted, oppressed to the fruit; stamens 4-8; filaments filiform; cotyledons accumbent.


Giant Knotweed (Fallopia sachalinensis)

Also known as Sachalin. The lesser-known of two beautiful but pernicious Japanese invaders, Giant Knotweed closely resembles its cousin the Japanese Knotweed (F. japonica), but can be distinguished by the leaves, which are longer and pointier and have a heart-shaped base rather than the rounded base of F. japonica. Like the Japanese Knotweed, Giant Knotweed can form large colonies that completely exclude other species of vegetation. These plants grew in an old German cemetery in Beechview, where they were blooming in the middle of September.

Because this imported weed was not so weedy in Gray’s time, we turn to the on-line Flora of North America at efloras.org:

Fallopia Adanson, Fam. Pl. 2: 277, 557. 1763.
[name conserved]

False-buckwheat [for Gabriello Fallopio, 1532-1562, Italian anatomist] Craig C. Freeman, Harold R. Hinds. Bilderdykia Dumortier.

Vines or herbs, annual or perennial; roots fibrous or woody; sometimes rhizomatous. Stems erect to scandent, rarely procumbent, glabrous or pubescent. Leaves deciduous, cauline, alternate, petiolate; ocrea persistent or deciduous, chartaceous; petiole base articulated, extrafloral nectaries sometimes present; blade broadly ovate to triangular, margins entire or wavy. Inflorescences terminal and spikelike, or terminal and axillary and paniclelike or racemelike, pedunculate or not. Pedicels present. Flowers bisexual, or bisexual and unisexual, some plants with bisexual flowers, other plants with only pistallate flowers 1-5 per ocreate fascicle, base stipelike; perianth usually accrescent in fruit, pale green or white to pink, campanulate, glabrous or, rarely, with blunt, hyaline hairs; tepals 5, connate nearly completely or only basally, petaloid, dimorphic, outer 3 winged or keeled, larger than inner 2; stamens 6-8; filaments distinct, free, glabrous or pubescent proximally; anthers yellow to pink or red, ovate to elliptic; styles 3, spreading, connate basally or nearly completely; stigmas capitate, fimbriate, or peltate. Achenes included or exserted, brown to dark brown or black, not winged, 3-gonous, glabrous. Seeds: embryo straight. x = 10, 11.

Species ca. 12 (8 in the flora): North America (including Mexico), South America, Europe, Asia, Africa.

Herbs, perennial, rhizomatous, 2-4(-5) m. Stems usually clustered, erect, sparingly branched, herbaceous, stiff, glabrous, glaucous. Leaves: ocrea persistent or deciduous, brownish, cylindric, 6-12 mm, margins oblique, face without reflexed and slender bristles at base, otherwise glabrous or puberulent; petiole 1-4 cm, glabrous; blade ovate-oblong, 15-30(-40) × 7-25 cm, base cordate, margins entire, glabrous or scabrous to ciliate, apex obtuse to acute, abaxial face minutely dotted, glaucous, with hairs along veins distinctly multicellular, 0.2-0.6 mm, tips acute to acuminate, adaxial face glabrous. Inflorescences axillary, mostly distal, erect or spreading, paniclelike, 3-8 cm, axes puberulent to pubescent; peduncle 0.1-4 cm or absent, puberulent to reddish-pubescent. Pedicels ascending or spreading, articulated proximal to middle, 2-4 mm, glabrous. Flowers bisexual or pistillate, 4-7 per ocreate fascicle; perianth accrescent in fruit, greenish, 4.5-6.5 mm including stipelike base, glabrous; tepals obovate to elliptic, apex obtuse to acute, outer 3 winged; stamens 6-8; filaments flattened proximally, glabrous; styles connate basally; stigmas fimbriate. Achenes included, brown, 2.8-4.5 × 1.1-1.8 mm, shiny, smooth; fruiting perianth glabrous, wings flat to undulate, 1.8-2.2 mm wide at maturity, decurrent on stipelike base to articulation, margins entire. 2n = 44, 66, 102, 132 (Japan, Korea).

Flowering Jul-Oct. Disturbed places; 0-500 m; introduced; B.C., N.B., Nfld. and Labr. (Nfld.), N.S., Ont., P.E.I., Que.; Calif., Conn., Del., Idaho, Ill., Ky., La., Maine, Md., Mass., Mich., Mont., N.J., N.Y., N.C., Ohio, Oreg., Pa., R.I., Tenn., Vt., Va., Wash., W.Va., Wis.; Asia (Japan); introduced in Europe.

Fallopia sachalinensis was introduced as a soil binder and garden ornamental. Like F. japonica, it spreads aggressively and has been declared noxious in California, Oregon, and Washington. It hybridizes with F. japonica, yielding F. ×bohemica. The mid-stem inflorescences of F. sachalinensis usually are shorter than the subtending leaves.


Climbing False Buckwheat (Fallopia scandens)

This ubiquitous vine looks a bit like a bindweed until it starts to bloom; then the characteristic clusters of tiny flowers of the knotweed clan reveal themselves. Like bindweeds, it likes to clamber over a fence or an arbor, or—as it did here—over the weeds and shrubbery at the edge of the woods. These vines were growing at the edge of an old cemetery in Beechview, where they were blooming in the middle of September.

Older botanists placed this genus in the large and polymorphous genus Polygonum. Gray describes that genus, the section Tinaria in which he places this species, and the species itself:

POLÝGONUM [Tourn ] L. KNOTWEED. Calyx 4-6(mostly 5)-parted; the divisions often petal-like, all erect in fruit, withering or persistent. Stamens 3-9. Styles or stigmas 2 or 3; achene accordingly lenticular or 3-angular. Embryo placed in a groove on the outside of the albumen and curved halfway around it; the radicle and usually the cotyledons slender. Pedicels jointed. — Ours all herbaceous, with fibrous roots (except in P. viviparum), flowering through late summer and early autumn. (Name composed of poly-, many, and gonu, knee, from the numerous joints.)

§ 6. TINIÀRIA Meisn. Twining (except dwarf var. of no. 29), unarmed; leaves ovate-heart-shaped; flowers in panicled racemes; outer calyx-lobes keeled or winged.

P. scándens L. (CLIMBING FALSE BUCKWHEAT.) Perennial, smooth; sheaths naked; leaves heart-shaped or slightly halberd-shaped, pointed; racemes interrupted, leafy; the 3 outer calyx-lobes strongly keeled and in fruit broadly winged, 10-15 mm. long; the wings often crisped, subentire; achene smooth and shining, 4 mm. long. (P. dumetorum, var. Gray.) — Moist thickets, common except on our northern borders. —Twining 2-4 m. over bushes. (Japan.)


Follow

Get every new post delivered to your Inbox.