Flora of North America species comparison

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Poteridium annuum

Rosaceae tribe Agrimonieae

annual burnet, prairie burnet, western burnet
Habit Plants winter-annual or biennial, glabrous; taproots 1–4(–6) dm. Herbs, perennial (annual or biennial in Poteridium) [shrubs or trees]; unarmed (hypanthia armed in Acaena).
Leaves

alternate, odd-pinnately compound;

stipules persistent (absent in Acaena), adnate to petiole (free in Poterium);

venation pinnate.
Flowers

perianth and androecium perigynous;

epicalyx bractlets absent;

hypanthium hemispheric, obconic, ovoid, urceolate, top-shaped, ellipsoid, nearly orbicular, or obtriangular;

torus absent;

carpels 1 or 2(or 3), rarely more, styles terminal, distinct;

ovule 1, apical.
Stamens

(2 or)4.

Fruits

hypanthia ridges extended into thin wings, 0.5 mm wide;

sepals tuberculose-thickened proximally.

achenes, enclosed within enlarged, often hardened, sometimes armed hypanthia;

styles deciduous, not elongate.

Poteridium annuum

Rosaceae tribe Agrimonieae
Phenology Flowering Mar–Jun; fruiting Apr–Jul.
Habitat Sandy and rocky soil, prairies, oak savannas, oak woodlands, disturbed areas (pastures, roadsides), often locally moister sites
Elevation 0–500 m (0–1600 ft)
Distribution
from FNA
AR; IA; KS; NY; OK; SC; TX; ON
[WildflowerSearch map]
[BONAP county map]
North America; Mexico; South America; West Indies (Hispaniola); Eurasia; Africa; Atlantic Islands; Indian Ocean Islands; Pacific Islands (New Zealand); Australia
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.)

Genera 12, species ca. 270 (5 genera, 17 species in the flora).

The base chromosome number for Agrimonieae is x = 7. Acaena and Sanguisorba are host to Phragmidium rusts. The tribal name Agrimonieae has priority over Sanguisorbeae, used by, among others, D. Potter et al. (2007). Agrimonieae also includes the genera Aremonia Necker ex Nestler (Europe), Cliffortia Linnaeus, Hagenia J. F. Gmelin and Leucosidea Ecklon & Zeyher (Africa), Margyricarpus Ruiz & Pavón and Polylepis Ruiz & Pavón (South America), and Spenceria Trimen (Asia) (Potter et al.).

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Key
1. Stems creeping or suberect; hypanthia spiny.
Acaena
1. Stems ascending to erect; hypanthia not spiny (rim bristly in fruit in Agrimonia)
→ 2
2. Inflorescences racemes (simple or compound); leaf blades with minor leaflet pairs between major pairs; petals 5 (yellow); hypanthial rim with 2–5 rows of bristles.
Agrimonia
2. Inflorescences spikes (cylindric, globose, or headlike); leaf blades without minor leaflet pairs between major pairs; petals 0; hypanthial rim without rows of bristles
→ 3
3. Leaflet margins pectinately pinnatisect.
Poteridium
3. Leaflet margins crenate, serrate, or incised
→ 4
4. Spikes headlike; flowers bisexual or pistillate (plants gynomonoecious); sepals distinct.
Poterium
4. Spikes ellipsoid to cylindric; flowers bisexual; sepals basally connate.
Sanguisorba
Source FNA vol. 9, p. 320. FNA vol. 9, p. 312. Author: Luc Brouillet.
Parent taxa Rosaceae > subfam. Rosoideae > tribe Agrimonieae > Poteridium Rosaceae > subfam. Rosoideae
Sibling taxa
P. occidentale
Subordinate taxa
Acaena, Agrimonia, Poteridium, Poterium, Sanguisorba
Synonyms Poterium annuum, Sanguisorba annua
Name authority (Nuttall) Spach: Ann. Sci. Nat., Bot., sér. 3, 5: 43. (1846) Lamarck & de Candolle: Syn. Pl. Fl. Gall., 333. (1806)
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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