Flora of North America species comparison

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Orbexilum

Orbexilum pedunculatum

leather-root, snakeroot or leather-root

Sampson's snakeroot
Habit Herbs, perennial, unarmed; with lignescent rhizome, tuber, or fusiform taproot. Herbs 6–8 dm; with ligneous, often tuberous, taproot or slender rhizome.
Stems

erect to ascending, usually gland-dotted, pubescent or glabrous.

densely strigose to glabrate.
Leaves

alternate, unifoliolate, palmate, or odd-pinnate;

stipules present, persistent or caducous;

petiolate;

stipels absent;

leaflets 1–7, blade margins entire, surfaces glandular-punctate or eglandular, pubescent or glabrous.

pinnately 3-foliolate;

stipules lanceolate to linear, 6–10 mm;

petiole 3–65 mm;

leaflet blades lanceolate to elliptic, 20–70 × 6–22 mm, surfaces eglandular or sparsely glandular-punctate, strigose.
Inflorescences

pedunculate, 5–50-flowered, terminal, spicate;

bracts present;

bracteoles absent.

columnar, 2–13 cm;

bracts lanceolate to narrowly ovate, 5–8 × 1–2.5 mm, eglandular.
Peduncles

4–16 cm.
Flowers

papilionaceous;

calyx tubular-campanulate, lobes 5, lobes 2–3 times tube length;

corolla violet, purple, or purplish blue, banner, wings, and keel well developed, keel connate apically;

stamens 10, diadelphous or proximally monadelphous;

anthers in 2 series, proximal dorsifixed, distal basifixed, introrse.

5–7 mm;

calyx 4–7 mm, eglandular, strigose;

corolla violet to purple, banner ovate.
Fruits

loments, dark brown to black, subsessile, asymmetric or curved, flattened, round-obovate to obovate, 0.4–1.2 cm, indehiscent, thickly leathery, rugose or papillose, glandular-punctate or eglandular, glabrous.

Legumes

3–5 × 3–4 mm, eglandular, rugose.
Seeds

1, reniform, obovate, depressed-obovate, or round-obovate.

round-obovate, 3–3.5 mm.
x

= 11.

2n

= 22.

Orbexilum

Orbexilum pedunculatum
Phenology Flowering May–Jul.
Habitat Open woods, grasslands.
Elevation 200–500 m. (700–1600 ft.)
Distribution
from USDA
c United States; se United States; Mexico
[BONAP county map]
from FNA
AL; AR; FL; GA; IL; IN; KY; LA; MO; MS; NC; NE; OH; OK; SC; TN; TX
[WildflowerSearch map]
[BONAP county map]
Discussion

Species 11 (8 in the flora).

As treated by J. W. Grimes (1990), Orbexilum comprises closely related species confined to North America, this largely confirmed by DNA data (A. N. Egan and K. A. Crandall 2008). B. L. Turner (2008b) proposed three additional species known from Mexico [O. chiapasanum B. L. Turner, O. melanocarpum (Bentham) Rydberg, and O. oliganthum (Brandegee) B. L. Turner], bringing to 11 the number of species recognized for the genus.

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

Orbexilum pedunculatum is allopatric with its closest relative, O. psoralioides, and the two taxa show little evidence of intergradation in regions of near contact (R. L. Wilbur 1963b; J. W. Grimes 1990; D. Isely 1990).

The combination Psoralea pedunculata (Miller) Vail (1894), which pertains here, is a later homonym of P. pedunculata Ker Gawler (1817) [= Otholobium sericeum (Poiret) C. H. Stirton (C. H. Stirton 1986)].

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Key
1. Leaves unifoliolate.
O. virgatum
1. Leaves 3–7-foliolate (sometimes unifoliolate in O. simplex).
→ 2
2. Leaves mostly palmately (3–)5–7-foliolate.
O. lupinellus
2. Leaves pinnately 3-foliolate (sometimes unifoliolate or palmately 5–7-foliolate in O. simplex).
→ 3
3. Leaflet blades: base cordate.
O. macrophyllum
3. Leaflet blades: base not cordate.
→ 4
4. Herbs eglandular; stipules narrowly oblong, 10–13 mm.
O. stipulatum
4. Herbs ± glandular-punctate, at least adaxial leaflet surfaces; stipules long-triangular, lanceolate, or linear, 3–10 mm.
→ 5
5. Legumes papillose or warty.
O. onobrychis
5. Legumes rugose.
→ 6
6. Flowers 8–10 mm.
O. simplex
6. Flowers 4–7 mm.
→ 7
7. Bracts, calyces, and legumes markedly glandular-punctate; bracts ovate, 5–8 × 2–4 mm; Atlantic Coastal Plain.
O. psoralioides
7. Bracts, calyces, and legumes eglandular; bracts lanceolate to narrowly ovate, 5–8 × 1–2.5 mm; sc United States.
O. pedunculatum
Source FNA vol. 11. Author: Billie L. Turner†. FNA vol. 11.
Parent taxa Fabaceae > subfam. Faboideae Fabaceae > subfam. Faboideae > Orbexilum
Sibling taxa
O. lupinellus, O. macrophyllum, O. onobrychis, O. psoralioides, O. simplex, O. stipulatum, O. virgatum
Subordinate taxa
O. lupinellus, O. macrophyllum, O. onobrychis, O. pedunculatum, O. psoralioides, O. simplex, O. stipulatum, O. virgatum
Synonyms Rhytidomene Hedysarum pedunculatum, Desmodium pedunculatum, O. pedunculatum var. eglandulosum, Psoralea eglandulosa, P. psoralioides var. eglandulosa
Name authority Rafinesque: Atlantic J. 1: 145. (1832) (Miller) Rydberg in N. L. Britton et al.: N. Amer. Fl. 24: 7. (1919)
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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