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California knotweed

knotweed, sharp-fruit knotweed

Habit Herbs. Plants green to blue-green, homophyllous.
Stems

erect, green, simple or divaricately branched, ± wiry, 4–40 cm, papillose-scabridulous.

prostrate to ascending, branched at proximal and middle nodes, not wiry, 20–100 cm.

Leaves

uniformly distributed, not articulated to ocreae, basal leaves usually caducous, distal leaves abruptly reduced to bracts;

ocrea 5–10 mm, glabrous or papillose-scabridulous, proximal part cylindric, distal part white or tawny, disintegrating into ± bristly-fringed fibers;

petiole absent;

blade 3-veined, without pleats, linear, 5–25(–30) × 0.5–2 mm, margins revolute, papillose-denticulate or smooth, apex mucronate or weakly spine-tipped.

ocrea 6.5–12 mm, proximal part cylindric, pruinose, distal part hyaline, soon disintegrating into brown fibers or nearly completely deciduous;

petiole 0–1 mm;

blade green to bluish green, elliptic-lanceolate to linear, 10–35 × 1.5–15 mm, margins flat or narrowly revolute, apex acute;

middle stem leaves slightly larger than adjacent branch leaves, distal leaves overtopping flowers.

Inflorescences

axillary;

cymes in distal axils, 1-flowered.

axillary, cymes uniformly distributed, 2–7-flowered.

Pedicels

absent.

exserted from ocreae, 2.5–5(–7) mm.

Flowers

open or closed;

perianth 2.5–3.5 mm;

tube 10–20% of perianth length;

tepals overlapping, uniformly white to pink, petaloid, elliptic, navicular, apex acute to acuminate;

midveins unbranched;

stamens 8.

semi-open;

perianth 3.5–5.5 mm;

tube 28–39% of perianth length;

tepals slightly overlapping, green, margins white to pink, petaloid, not keeled, oblong to obovate, not cucullate;

veins branched;

stamens 8.

Achenes

enclosed in or slightly exserted from perianth, brown, narrowly elliptic, 1.8–2.2 mm, faces subequal, shiny, smooth.

exserted from perianth, pale brown to dark brown, ovate, 3-gonous, (3.5–)4.1–5.5(–6.5) mm, faces subequal, apex not beaked, edges straight, shiny, smooth or with fine tubercles especially toward apex; late-season achenes unknown.

Polygonum californicum

Polygonum oxyspermum

Phenology Flowering May–Sep.
Habitat Open places, including serpentine
Elevation 40-1200 m (100-3900 ft)
Distribution
from FNA
CA; OR
[WildflowerSearch map]
[BONAP county map]
from FNA
ME; NB; NF; NS; PE; QC; Europe
[BONAP county map]
Discussion

Subspecies 3 (2 in the flora).

The treatment by D. A. Webb and A. O. Chater (1963) of the Polygonum oxyspermum complex is followed here. T. Karlsson (2000) accepted P. raii and P. oxyspermum as distinct species.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Key
1. Ocreae with prominent veins, distal part disintegrating, veins persistent; leaf blades 5-8 times as long as wide; achenes 4.1-5.5(-6.5) mm, exserted 1-2.5 mm from perianth
subsp. oxyspermum
1. Ocreae without prominent veins, distal part disintegrating, nearly completely deciduous; leaf blades 3.5-5 times as long as wide; achene (3.5-)4-5 mm, exserted 0.5-1.3(-1.8) mm from perianth
subsp. raii
Source FNA vol. 5, p. 564. FNA vol. 5, p. 554.
Parent taxa Polygonaceae > subfam. Polygonoideae > Polygonum > sect. Duravia Polygonaceae > subfam. Polygonoideae > Polygonum > sect. Polygonum
Sibling taxa
P. achoreum, P. argyrocoleon, P. austiniae, P. aviculare, P. bidwelliae, P. bolanderi, P. cascadense, P. douglasii, P. engelmannii, P. erectum, P. fowleri, P. glaucum, P. heterosepalum, P. hickmanii, P. humifusum, P. majus, P. marinense, P. minimum, P. nuttallii, P. oxyspermum, P. paronychia, P. parryi, P. patulum, P. plebeium, P. polygaloides, P. ramosissimum, P. sawatchense, P. shastense, P. spergulariiforme, P. striatulum, P. tenue, P. utahense
P. achoreum, P. argyrocoleon, P. austiniae, P. aviculare, P. bidwelliae, P. bolanderi, P. californicum, P. cascadense, P. douglasii, P. engelmannii, P. erectum, P. fowleri, P. glaucum, P. heterosepalum, P. hickmanii, P. humifusum, P. majus, P. marinense, P. minimum, P. nuttallii, P. paronychia, P. parryi, P. patulum, P. plebeium, P. polygaloides, P. ramosissimum, P. sawatchense, P. shastense, P. spergulariiforme, P. striatulum, P. tenue, P. utahense
Subordinate taxa
P. oxyspermum subsp. oxyspermum, P. oxyspermum subsp. raii
Synonyms Duravia californica, P. greenei
Name authority Meisner: in A. P. de Candolle and A. L. P. P. de Candolle, Prodr. 14: 100. (1856) C. A. Meyer & Bunge ex Ledebour: Index Seminum (Dorpat) 1824: 5. (1824)
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