Flora of North America species comparison

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Poteridium annuum

Poteridium occidentale

annual burnet, prairie burnet, western burnet

annual burnet, western burnet
Habit Plants winter-annual or biennial, glabrous; taproots 1–4(–6) dm. Plants winter-annual, glabrous; taproots 3–10 dm.
Stamens

(2 or)4.

2(or 4).
Fruits

hypanthia ridges extended into thin wings, 0.5 mm wide;

sepals tuberculose-thickened proximally.

hypanthia ridges rounded, thickened;

sepals not thickened proximally.

Poteridium annuum

Poteridium occidentale
Phenology Flowering Mar–Jun; fruiting Apr–Jul. Flowering May–Jul; fruiting Jun–Aug.
Habitat Sandy and rocky soil, prairies, oak savannas, oak woodlands, disturbed areas (pastures, roadsides), often locally moister sites Prairies, sandy open ground, sagebrush flats, vernal pools, drawdown shorelines of streams and lakes, grassy clearings, roadsides, particularly with surficial or subterranean moisture
Elevation 0–500 m (0–1600 ft) 10–2100 m (0–6900 ft)
Distribution
from FNA
AR; IA; KS; NY; OK; SC; TX; ON
[WildflowerSearch map]
[BONAP county map]
from FNA
AZ; CA; ID; MT; NM; NV; OR; WA; WY; BC
[WildflowerSearch map]
Discussion

The eastern records (Ontario, Iowa, Massachusetts, New York, and South Carolina) all appear to represent adventives or non-persistent waifs. A record from Maryland (J. B. S. Norton and R. G. Brown 1946) is plausible; no specimen is known to the author.

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

The taxonomic status of Poteridium occidentale has been controversial. Most floristicians of the twentieth century accepted it as distinct from the more eastern P. annuum (usually treating the two in Sanguisorba); but in recent decades a trend developed to merge the two taxa. While superficially similar, they seem to represent independent evolutionary lineages, as indicated by morphologic distinctions and allopatric distributions.

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Source FNA vol. 9, p. 320. FNA vol. 9, p. 320.
Parent taxa Rosaceae > subfam. Rosoideae > tribe Agrimonieae > Poteridium Rosaceae > subfam. Rosoideae > tribe Agrimonieae > Poteridium
Sibling taxa
P. occidentale
P. annuum
Synonyms Poterium annuum, Sanguisorba annua Sanguisorba occidentalis
Name authority (Nuttall) Spach: Ann. Sci. Nat., Bot., sér. 3, 5: 43. (1846) (Nuttall) Rydberg: in N. L. Britton et al., N. Amer. Fl. 22: 388. (1908)
Web links 
Unless otherwise noted, all data comes from the online version of the Flora of North America, who have made most of their content available via a Creative Commons license (CC BY 4.0).



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