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American jointweed, southern jointweed

october-flower

Habit Subshrubs, perennial, synoecious, 5.5–9 dm. Subshrubs, perennial, dioecious, 1.5–7 dm.
Stems

erect, branched proximally and basally, glabrous.

erect or decumbent, usually branched proximally and distally, glabrous or minutely pubescent.

Leaves

persistent;

ocrea margins not ciliate;

blade linear to spatulate, (4–)5–12(–19) × 0.5–0.9(–1.2) mm, base barely tapered, margins not hyaline, apex obtuse to acute, often erose, glabrous.

persistent;

ocrea margins not ciliate;

blade linear to narrowly clavate or broadly spatulate, (3–)4–16(–36) × (0.3–)0.6–3.6(–5) mm, base barely tapered to attenuate, margins hyaline at least along distal 1/2, apex obtuse, glabrous.

Inflorescences

(7–)18–30(–60) mm;

ocreola encircling rachis, only the base adnate to rachis, apex acuminate.

(2–)4–20(–33) mm;

ocreola encircling rachis, only the base adnate to rachis, apex acute to acuminate.

Pedicels

spreading in anthesis and fruit, 0.4–2.3 mm, usually much longer than subtending ocreola.

spreading in anthesis, spreading to reflexed in fruit, 0.2–0.9 mm, as long or much longer than subtending ocreola.

Flowers

bisexual;

outer tepals sharply reflexed early in anthesis and in fruit, white to pink, elliptic to ovate, 1.2–2.2 mm in anthesis, margins erose;

inner tepals loosely appressed in anthesis and fruit, white to pink, ovate to suborbiculate, 1.7–2.9 mm in anthesis, margins erose;

filaments dimorphic;

anthers yellow or pink;

styles and stigmas 0.5–1 mm in anthesis.

functionally unisexual;

filaments dimorphic;

anthers pink, orange, or yellow;

styles and stigma ca. 0.1 mm in anthesis.

Staminate flowers

outer tepals loosely appressed in anthesis, reflexed in fruit, white, broadly elliptic, 0.9–1.8 mm in anthesis, margins entire;

inner tepals appressed in anthesis and fruit, white, elliptic, 0.9–1.7 mm in anthesis, margins entire.

Pistillate flowers

outer tepals loosely appressed in anthesis, usually reflexed in fruit, white to pink, often drying yellow, broadly elliptic to ovate, 0.5–1.3 mm in anthesis, margins entire;

inner tepals appressed in anthesis and fruit, white to pink, often drying yellow or red, broadly elliptic to ovate, 0.6–1.5 mm in anthesis, margins entire.

Achenes

included, reddish brown, 3(–4)-gonous, 2.5–4 × 1.3–2.3 mm, shiny, smooth.

mostly included, brown to yellow-brown, 3-gonous, 1.3–2.1 × 0.7–1.2 mm, shiny, smooth.

2n

= 36.

= 28.

Polygonella americana

Polygonella polygama

Phenology Flowering Jun–Oct.
Habitat Sandy roadsides, fields, riverbanks, scrub forests, waste places
Elevation 10-200 m (0-700 ft)
Distribution
from FNA
AL; AR; GA; LA; MO; NM; OK; SC; TX
[WildflowerSearch map]
from FNA
AL; FL; GA; MS; NC; SC; TX; VA
[WildflowerSearch map]
Discussion

Varieties 3 (3 in the flora).

J. H. Horton (1963) found considerable intergradation among characters used by J. K. Small (1933) to separate Polyonella polygama, P. brachystachya, and P. croomii. He included the latter two taxa in P. polygama. R. P. Wunderlin (1981) as well as G. L. Nesom and V. M. Bates (1984) discussed morphological variation among these geographically distinct entities and recognized three varieties.

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

Key
1. Ocreae with apex acuminate, tip 1-1.5 mm; leaf blades usually 0.5-1 mm wide
var. croomii
1. Ocreae with apex obtuse to acute, tip 0.1-0.5 mm; leaf blades 0.5-6 mm wide
→ 2
2. Leaf blades 0.5-1 mm wide
var. brachystachya
2. Leaf blades (2-)3-6 mm wide
var. polygama
Source FNA vol. 5, p. 539. FNA vol. 5, p. 538.
Parent taxa Polygonaceae > subfam. Polygonoideae > Polygonella Polygonaceae > subfam. Polygonoideae > Polygonella
Sibling taxa
P. articulata, P. basiramia, P. ciliata, P. fimbriata, P. gracilis, P. macrophylla, P. myriophylla, P. parksii, P. polygama, P. robusta
P. americana, P. articulata, P. basiramia, P. ciliata, P. fimbriata, P. gracilis, P. macrophylla, P. myriophylla, P. parksii, P. robusta
Subordinate taxa
P. polygama var. brachystachya, P. polygama var. croomii, P. polygama var. polygama
Synonyms Gonopyrum americanum Polygonum polygamum
Name authority (Fischer & C. A. Meyer) Small: Mem. Torrey Bot. Club 5: 141. (1894) (Ventenat) Engelmann & A. Gray: Boston J. Nat. Hist. 5: 231. (1845)
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