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Aquatic and Wetland Vascular Plants of the Northern Great Plains

Polygonum L.-- Smartweed, knotweed, tear-thumb

Erect to sprawling, often weedy annuals and perennials, the stems often swollen at the nodes. Leaves sessile to short-petioled, the blades generally lanceolate to oblanceolate or elliptic (sagittate in P. sagittatum); stipules fused to form a tubular or 2-lobed ocrea which sheaths the stem above each node, the ocreae (pl.) membranous or chartaceous, often lacerate or completely broken up at older nodes, sometimes fringed with bristles. Flowers small, greenish, whitish or pinkish, usually borne in spikelike racemes, or (in P. ramosissimum) the flowers in axillary positions, with 1-few flowers in the axils of ordinary leaves; in those spp. with flowers in racemes, the racemes terminal or both terminal and axillary, loosely to densely flowered, the flowers fascicled in the axils of small bracts (ocreolae), the pedicels included by or barely surpassing the ocreolae. Sepals usually 5(4-6), petaloid throughout or at least around the margins, greenish-white to deep pink (green with yellowish or pinkish margins in P. ramosissimum), somewhat accrescent, united near or well below the middle; stamens 8 or fewer; styles 2-3. Achenes brown to black, lenticular or trigonous, sometimes both in the same inflorescence, apiculate, surrounded by the persistent sepals.

Martens, T. R. and P. H. Raven.  1965.  Taxonomy of Polygonum, 
	section Polygonum (Avicularia) in North America.  Madrono 18:85-92. 

Stanford, E. E.  1925.  The amphibious group of Polygonum, subgenus 
	Persicaria. Rhodora 27:109-112, 125-130, 146-152, 156-166.

Lead Characteristic Go To
1 Leaves sagittate; stems armed with reflexed prickles. P. sagittatum
1 Leaves generally lanceolate to oblanceolate or elliptic; stems unarmed. Lead 2
2 Flowers strictly axillary, with 1-few in the upper axils; leaves jointed at the base. P. ramosissimum
2 Flowers all or mostly in spikelike racemes; leaves not jointed at the base. Lead 3
3 Racemes strictly terminal, solitary or paired (rarely 3 or 4) at the tips of stems; plants perennial; flowers rose pink. Lead 4
3 Racemes terminal and axillary, often numerous on the stems; plants annual (except P. hydropiperoides); flowers white, greenish-white or pink. Lead 5
4 Racemes globose to short-cylindric, mostly 1-3.5 cm long; peduncles usually glabrous P. amphibium
4 Racemes cylindric, mostly 4-12 cm long; peduncles usually glandular-pubescent P. coccineum
5 Ocreae entire or lacerate. Lead 6
5 Ocreae fringed with bristles. Lead 8
6 Outer sepals strongly 3-nerved, each nerve ending in an anchor-shaped fork; racemes nodding to erect. P. lapathifolium
6 Outer sepals with faint, irregularly forked nerves; racemes erect. Lead 7
7 Stamens and styles unequal, either the stamens or styles exserted conspicuously beyond the perianth. P. bicorne
7 Stamens and styles equal or nearly so, both included in or equaling the perianth. P. pensylvanicum
8 Calyx conspicuously glandular-punctate on the outside. Lead 9
8 Calyx not glandular-punctate, or inconspicuously glandular on the inner sepals only. Lead 10
9 Ocreae gibbous, concealing cleistogamous flowers; achenes brown to dark brown, dull. P. hydropiper
9 Ocreae cylindrical; cleistogamous flowers none; achenes black, smooth and shiny. P. punctatum
10 Plants perennial; racemes slender, often interrupted, commonly exceeding 3 cm long; achenes all trigonous. P. hydropiperoides
10 Plants annual; racemes rather thick and dense, mostly continuous, rarely reaching 3 cm long; achenes mostly lenticular, some often trigonous. P. persicaria

15. Polygonaceae, the Smartweed Family
1. Polygonum L. -- Smartweed, knotweed, tear-thumb
1. Polygonum amphibium L. -- Water smartweed
2. Polygonum bicorne Raf.-- Pink smartweed
3. Polygonum coccineum Muhl. ex Willd.-- Marsh smartweed
4. Polygonum hydropiper L.-- Water pepper
5. Polygonum hydropiperoides Michx.-- Mild water pepper
6. Polygonum lapathifolium L.-- Pale smartweed
7. Polygonum pensylvanicum L.-- Pennsylvania smartweed
8. Polygonum persicaria L.-- Lady's thumb
9. Polygonum punctatum Ell.-- Water smartweed
10. Polygonum ramosissimum Michx.-- Bushy knotweed
11. Polygonum sagittatum L.-- Tear-thumb, arrow-vine

Return to Family -- Polygonaceae - The Smartweed Family
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