Common Persicaria, Pink Knotweed, Smartweed – Flowers

(Polygonum Pennsylvanicum) Buckwheat family

Flowers—Very small, pink, collected in terminal, dense, narrow, obtuse spikes, 1 to 2 in. long. Calyx pink or greenish, 5-parted, like petals; no corolla; stamens 8 or less; style 2-parted. Stem : 1 to 3 ft. high, simple or branched, often partly red, the joints swollen and sheathed; the branches above, and peduncles glandular. Leaves: Oblong, lance-shaped, entire edged, 2 to 11 in. long, with stout midrib, sharply tapering at tip, rounded into short petioles below.

Preferred Habitat—Waste places, roadsides, moist soil.

Flowering Season—July—October.

Distribution—Nova Scotia to the Gulf of Mexico ; westward to Texas and Minnesota.

Everywhere we meet this commonest of plants or some of its similar kin, the erect pink spikes brightening roadsides, rubbish heaps, fields, and waste places, from midsummer to frost. The little flowers, which open without method anywhere on the spike they choose, attract many insects, the smaller bees (Andrena) conspicuous among the host. As the spreading divisions of the perianth make nectar-stealing all too easy for ants and other crawlers that would not come in contact with anthers and stigma where they enter a flower near its base, most buckwheat plants whose blossoms secrete sweets protect themselves from theft by coating the upper stems with glandular hairs that effectually discourage the pilferers. Shortly after fertilization, the little rounded, flat-sided fruit begins to form inside the persistent pink calyx. At any time the spike-like racemes contain more bright pink buds and shining seeds than flowers. Familiarity alone breeds contempt for this plant, that certainly possesses much beauty.

The Lady’s Thumb (P. Persicaria), often a troublesome weed, roams over the whole of North America, except at the extreme north—another illustration of the riotous profusion of European floral immigrants rejoicing in the easier struggle for existence here. Its pink spikes are shorter and less slender than those of the preceding taller, but similar species, and its leaves, which are nearly seated on the stem, have dark triangular or lunar marks near the centre in the majority of cases.

An insignificant little plant, found all over our continent, Europe, and Asia, is the familiar Knot-grass or Doorweed (P. aviculare), often trailing its leafy, jointed stems over the ground, but at times weakly erect, to display its tiny greenish or white pink-edged flowers, clustered in the axils of oblong, bluish-green leaves that are considerably less than an inch long. Although in bloom from June to October, insects seldom visit it, for it secretes very little, if any, nectar. As might be expected in such a case, its stem is smooth.

When the amphibious Water Persicaria (P. amphibium) lifts its short, dense, rose-colored ovoid or oblong club of bloom above ponds and lakes, it is sufficiently protected from crawling pilferers, of course, by the water in which it grows. But suppose the pond dries up and the plant is left on dry ground, what then ? Now, a remarkable thing happens: protective glandular, sticky hairs appear on the epidermis of the leaves and stems, which were perfectly smooth when the flowers grew in water. Such small wing-less insects as might pilfer nectar without bringing to their hostess any pollen from other blossoms are held as fast as on bird-lime. The stem, which sometimes floats, sometimes is immersed, may attain a length of twenty feet ; the rounded, elliptic, petioled leaves may be four inches long or only half that size. From Quebec to New jersey, and westward to the Pacific, the solitary, showy in-florescence, which does well to attain a height of an inch, may be found during July and August.

Throughout the summer, narrow, terminal, erect, spike-like racemes of small, pale pink, flesh-colored, or greenish flowers are sent upward by the Mild Water Pepper (P. hydropiperoides). It is like a slender, pale variety of the common pink persicaria. One finds its inconspicuous, but very common, flowers from June to September. The plant, which grows in shallow water, swamps, and moist places throughout the Union and consider-ably north and south of it, rises three feet or less. The cylindric sheaths around the swollen joints of the stem are fringed with long bristles—a clue to identification. Another similar Water Pepper or Smartweed (P. hydropiper) is so called because of its acrid, biting juice.

The Climbing False Buckwheat (P. scandens) straggles over bushes in woods, thickets, and by the waysides throughout a very wide range ; yet its small, dull, greenish-yellow and pinkish flowers, loosely clustered in long pedicelled racemes, are so inconspicuous during August and September, when the showy composites are in their glory, that we give them scarcely a glance. The alternate leaves, which are heart-shaped at the base and pointed at the lip, suggesting those of the morning glory, are on petioles arising from sheaths over the enlarged joints which, in this family, are always a most prominent characteristic—(Poly = many, gonum = a knee). The three outer sepals, keeled when in flower, are irregularly winged when the three-angled, smooth achene hangs from the matured blossom in autumn, the season at which the vine assumes its greatest attractiveness.

The Arrow-leaved Tear Thumb (P. sagittatum), found in ditches and swampy wet soil, weakly leans on other plants, or climbs over them with the help of the many sharp, recurved prickles which arm its four-angled stem. Even the petioles and under side of the leaf’s midrib are set with prickles. The light green leaves, that combine the lance and the arrow shapes, take on a beautiful russet-red tint in autumn. The little, five-parted rose-colored or greenish-white flowers grow in small, close terminal heads from July to September from Nova Scotia to the Gulf and far westward.

Seaside or Coast Jointweed or Knot-grass (Polygonella articulata)—Polygonum articulatum of Gray—a low, slender, wiry, diffusely spreading little plant, with thread-like leaves seated on its much jointed stem, rises cleanly from out the sand of the coast from Maine to Florida, and the shores of the Great Lakes. Very slender racemes of tiny, nodding, rose-tinted white flowers, with a dark midrib to each of the five calyx segments, are insignificant of themselves ; but when seen in masses, from July to October, they tinge the upper beaches and sandy meadows with a pink blush that not a few artists have transferred to the fore-ground of their marine pictures.