Polygonum polygaloides ssp. confertiflorum (Nutt. ex Piper) Hickman
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Family: Polygonaceae
Genus: Polygonum
Species Synonyms: Polygonum confertiflorum Nutt. ex Piper
Polygonum imbricatum Nutt.
Polygonum kelloggii var. confertiflorum (Nutt. ex Piper) Dorn
Polygonum watsonii Small
Common Names: dense-flowered knotweed
Watson’s knotweed
white-margined knotweed
Canada: southwestern Saskatchewan
Saskatchewan: southwestern Saskatchewan; Altawan – Cypress Hills
Ecoregion: Cypress Upland, Mixed Grassland
Saskatchewan: moist to dried prairie depressions, slough bottom mudflats, and drying field potholes
Associated Species: bristly mousetail, Douglas knotweed, Douglas sedge, graceful cinquefoil, meadow woollyheads, needle spikerush, onespike oatgrass, purslane speedwell, stiff goldenrod
Provincial Status According
to Harms (2003):
Nature Conservancy Status:
Saskatchewan Species at
Risk Status:
Dense-flowered knotweed is threatened because of rarity in Saskatchewan. Some local populations are small and some larger. Possible threats have been identified for this species.
Height: 6 – 20 cm
Stems: erect, branched, rarely simple, green, hairless
Leaves: basal and on the stem, basal leaves often falling off early, stem leaves uniformly distributed, sessile, 10 – 40 mm long, 1 – 2.5 mm wide, narrowly linear, base jointed with petiole, 3-veined, margin rolled; fused stipules 4 – 8 mm long, thin, membranous, 2-lobed, hairless, veins inconspicuous
Inflorescence: axillary and terminal, spike-like, oval to cylindrical, flowers 1 – 3 per sheath
Flowers: mostly closed; perianth 1.5 – 3 mm long, overlapping, white, pink or red, with conspicuous white margin; stamens 3
Fruits: single-seeded, dry brown to dark brown, shiny or dull
1 Flowers solitary or in small axillary clusters; leaves jointed at the base with the stalk, small; outer tepals may be boat-shaped; fused stipules often dry and membranous, 2-lobed
1 Flowers in spike-like clusters; leaves not jointed at the base with the stalk, large; outer tepals may be winged or unwinged, but not boat-shaped (except in P. cilinode and P. convolvulus); fused stipules papery
2 Inflorescence compact
2 Inflorescence a slender, open, unbranched
3 Fruits black, smooth and shiny; tepals rounded
P. spergulariiforme
3 Fruits yellowish to dark brown, not shiny; tepals pointed
4 Bracts definitely white-margined; stems to 20 cm tall
P. polygaloides var. confertiflorum
4 Bracts only slightly white-margined, if at all; stems less than 20 cm
P. polygaloides var. kelloggii
5 Flowers on reflexed stalks
P. douglasii ssp. douglasii
5 Flowers ascending or spreading
6 Fruits shiny; leaves linear to lance-shaped
P. ramosissimum
6 Fruits dull; leaves oval
7 Tepals bottle-shaped, outer tepal hooded
P. achoreum
7 Tepals not constricted below the tip, outer tepal not hooded
8 Leaves on the branches the same size as the ones attached directly to the stem; sepals with greenish-white or pink margins
P. arenastrum (= P. aviculare ssp. depressum)
8 Leaves on the branches much smaller than the ones attached directly to the stem; sepals with white, pink or purple margins
P. aviculare
9 Stems slender and twining; leaves broad, base arrow-shaped
9 Stems not twining; leaves linear to lance-shaped, base not arrow-shaped
10 Fused stipules with a ring of bristles
P. cilinode (= Fallopia cilinodes)
10 Fused stipules lacking bristles
11 Fruiting sepals to 5 mm long, wings small; plants annual
P. convolvulus var. convolvulus (= Fallopia convolvulus)
11 Fruiting sepals to 1.5 cm long, wings broad; plants perennial
P. scandens var. scandens (= Fallopia scandens)
12 Leaves mainly basal, stem leaves few and reduced
P. viviparum (= Bistorta vivipara)
12 Leaves mainly on the stem, well-developed
13 Fused stipules with bristles at the summit
13 Fused stipules without bristles
14 Rhizomes forking; perennials; fused stipules expanded at the top to create a rim; spikes to 2 cm thick; tepals not glandular
P. amphibium var. stipulaceum (= Persicaria amphibia)
14 Roots fibrous; fused stipules not expanded at the top; spikes slender, less than 2 cm thick; tepals glandular
P. punctatum var. confertiflorum (= Persicaria punctata)
15 Annuals, terrestrial; roots fibrous; spikes terminal and axillary, numerous
P. lapathifolium var. lapathifolium (= Persicaria lapathifolia)
15 Perennials, often aquatic; rhizomes forking; spikes terminal, solitary or paired
16 Leaf stalks attached near base of fused stipules; leaves and upper stems hairless to sparsely straight-hairy
P. coccineum var. coccineum (= Persicaria amphibia)
16 Leaf stalks attached midway on fused stipules; leaves and upper stems densely ashy-gray hairy
P. coccineum var. pratincola (= Persicaria amphibia)