Polygonum cascadense |
Polygonum glaucum |
|
---|---|---|
Cascade knotweed |
seabeach knotweed, seaside knotweed |
|
Habit | Herbs. | Plants silvery, homophyllous. |
Stems | spreading to erect, zigzagged, green, simple or branched from base, wiry, 5–12(–15) cm, glabrous. |
prostrate to ascending, branched from base, not wiry, 20–70 cm. |
Leaves | uniformly distributed, articulated to ocreae, basal leaves persistent, distal leaves abruptly reduced to bracts; ocrea 2–5 mm, glabrous, proximal part funnelform, distal part lacerate; petiole essentially absent; blade 1-veined, not pleated, oblanceolate to obovate, 5–20 × 2–5 mm, margins revolute, never touching along midrib, sparsely papillose-denticulate, apex rounded or apiculate. |
ocrea persistent, 7–15 mm, proximal part cylindric, pruinose, distal parts silvery, margins overlapping, entire or lacerate; petiole 0.5–3 mm; blade bluish green, lanceolate, 10–30 × 2–8 mm, coriaceous, margins revolute, apex obtuse or acute, rugulose when fresh, markedly rugulose when dried, glaucous; middle stem leaves slightly larger than adjacent branch leaves, distal leaves overtopping flowers they subtend. |
Inflorescences | axillary and terminal, spikelike, dense; cymes congested at tips of stems and branches, 3–5-flowered. |
axillary; cymes uniformly distributed, 1–3-flowered. |
Pedicels | enclosed in ocreae, erect to spreading, 2–3 mm. |
enclosed in ocreae, 3–5 mm. |
Flowers | open; perianth 2–2.5 mm; tube 12–25% of perianth length; tepals overlapping, uniformly white, petaloid, oblong to obovate, cucullate, navicular in distal 1/4, apex rounded; midveins unbranched; stamens 8. |
semi-open; perianth (2–)3–4 mm; tube 12–26% of perianth length; tepals ± recurved, overlapping, white, margins white or pink, petaloid, not keeled, oblong-obovate to spatulate, not cucullate; midvein usually unbranched; stamens 8. |
Achenes | enclosed in or exserted from perianth, black, ovate to ovate-oblong, 1.8–2.1 mm, faces subequal, shiny, smooth. |
exserted from perianth, reddish brown to dark brown, ovate, 3-gonous, 2.5–3(–4) mm, faces subequal, apex not beaked, edges straight, shiny, smooth; late-season achenes common, 3–5 mm. |
2n | = 40. |
|
Polygonum cascadense |
Polygonum glaucum |
|
Phenology | Flowering Jun–Sep. | Flowering Jul–Nov. |
Habitat | Dry, usually rocky slopes, often on serpentine | Coastal beaches, sand dunes, margins of salt ponds |
Elevation | 1600-1800 m (5200-5900 ft) | 0-10 m (0-0 ft) |
Distribution |
OR
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CT; DC; DE; FL; GA; MA; MD; NC; NJ; NY; RI; SC; VA |
Discussion | Polygonum glaucum is restricted to maritime beaches along the Atlantic coast from Massachusetts south to Georgia. Over most of its range it is rare and declining; populations on coastal islands of Massachusetts and along the shore of Long Island appear to be secure. Seabeach knotweed appears to be related to P. oxyspermum. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
|
Source | FNA vol. 5, p. 571. | FNA vol. 5, p. 553. |
Parent taxa | Polygonaceae > subfam. Polygonoideae > Polygonum > sect. Duravia | Polygonaceae > subfam. Polygonoideae > Polygonum > sect. Polygonum |
Sibling taxa | ||
Name authority | W. H. Baker: Madroño 10: 62, plate 1, fig. 1. (1949) | Nuttall: Gen. N. Amer. Pl. 1: 254. (1818) |
Web links |