Astragalus purshii Dougl. ex Hook.
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TAXONOMY
 
Family: Fabaceae
Genus: Astragalus
 
Species Synonyms: none
Common Names: Pursh’s milkvetch
Pursh locoweed
woollypod milkvetch
 
DISTRIBUTION
 
Canada: southern British Columbia – southern Alberta – southwestern Saskatchewan
Saskatchewan: southwestern Saskatchewan; Great Sand Hills – Watrous
Ecoregion: Cypress Upland, Mixed Grassland, Moist Mixed Grassland
 
HABITAT
 
Saskatchewan: eroded, short grassland and mixed prairie
 
RARITY STATUS
 
Provincial Status According
to Harms (2003):
Threatened
Nature Conservancy Status:
G5 S2
Saskatchewan Species at
Risk Status:
Threatened
COSEWIC Status:
None
 
Pursh’s milkvetch is threatened in Saskatchewan because it is rare or uncommon and somewhat regionally restricted in the province. Local population sizes vary. Possible threats have been identified for this species.
 
SPECIES DESCRIPTION
 
Roots: taproot
Stems: caudex branched; stems densely tufted, cushion-like or short-creeping, usually < 5 cm tall, densely long-hairy and woolly
Stipules: 3 – 15 mm long, exceeding internodes, membranous
Leaves: stalk slender; leaves 1 – 12 cm long, odd-pinnate, hairs white and silky
Leaflets: 5 – 17, elliptic to oval, silky hairy
Inflorescence: unbranched, short, 2 – 10-flowered; inflorescence stalk 0 – 10 cm long
Flowers: sepal tube 9 – 13 mm long, cylindrical; petals ca. 2 cm long, yellowish white; banner 19 – 26 mm long; wing 17 – 22 mm long; keel 15 – 21 mm long, purple-tipped; stamens 10, 9 + 1 arrangement; ovary superior
Fruits: pod sessile, spreading, densely long-hairy and woolly; seeds 2 – 3 mm long, brown, often purple-spotted, smooth
 
ASTRAGALUS KEY FOR GENERA FOUND IN SASKATCHEWAN
 
1 Leaves needle-like, distinctly spine-tipped
A. kentrophyta var. kentrophyta
1 Leaves not needle-like or spine-tipped
2
   
2 Plants without a distinct stem, < 10 cm tall, densely tufted; flowers often included among leaves
3
2 Plants with a distinct stem, > 10 cm tall, may be erect or creeping, stem not well defined in A. missouriensis; flowers in distinct inflorescences
6
 
3 Leaves simple or with 1 or 2 linear leaflets
A. spatulatus
3 Leaves pinnate or with 3 leaflets
4
 
4 Leaves with 3 leaflets
A. gilviflorus var. gilviflorus
4 Leaves pinnate
 
5 Leaf hairs attaching in the middle, with one side longer than the other; leaflets 4 – 5x as long as wide, tip acute
A. lotiflorus
5 Leaf hairs attaching at the base; leaflets 2x as long as wide, tip rounded
A. purshii var. purshii
 
6 Leaf hairs attaching in the middle, with one side longer than the other
7
6 Leaf hairs attaching at the base
9
 
7 Petals greenish-white or creamy; plants green
A. canadensis var. canadensis
7 Petals purplish; plants covered in greyish or silvery hairs
8
 
8 Leaflets in up to 12 pairs; plants with a definite stem; stipules fused
A. adsurgens ssp. robustior
8 Leaflets fewer than or equal to 7 pairs; stem not well-defined; stipules not fused
A. missouriensis var. missouriensis
 
9 Petals yellow, cream or orange, keel occasionally blue-tinged
10
9 Petals blue, pink, or purple
18
 
10 Leaves and stems gray-hairy, hairs 1 – 2 mm long, widely spreading
A. drummondii
10 Hairs of leaves and stem variable but hairs shorter than 1 mm long
11
 
11 Pods hairless or nearly to
12
11 Pods distinctly hairy
15
 
12 Pods sessile or nearly so, stalk < 1 mm long; pods very fleshy, walls thick, hard and bony when dry
A. crassicarpus
12 Pods stalked, stalk equal to or exceeding sepals; pods not fleshy, walls thin
13
 
13 Pods linear
A. racemosus var. racemosus
13 Pods broader
14
 
14 Leaflets 2 – 4 cm long; pods inflated and nearly round in cross section
A. americanus
14 Leaflets < 2 cm long; pods very strongly flattened
A. tenellus
 
15 Flowers small, sepal tube 1.5 – 4.5 mm long, banner 4 – 12.5 mm long
16
15 Flowers large, sepal tube > 4.5 mm long, banner > 13 mm long
17
 
16 Pods hanging down, stalked
A. alpinus var. alpinus
16 Pods erect, short-stalked
A. bodinii
 
17 Leaflets without stalks; pods sessile
A. pectinatus
17 Leaflets with stalks; pods stalked
A. agrestis
 
18 Pods 1 – 3 cm long
19
18 Pods generally less than 1.1 cm long
20
 
19 Pods with two deep grooves on upper side
A. bisulcatus
19 Pods lacking two deep grooves
A. flexuosus var. flexuosus
 
20 Pods spreading to erect
21
20 Pods spreading to deflexed
22
 
21 Flowers small, sepal tube < 4.5 mm long, banner < 13 mm long
A. bodinii
21 Flowers large, sepal tube > 4.5 mm long, banner > 13 mm long
A. agrestis
 
22 Pods plump
A. gracilis
22 Pods strongly flattened laterally
23
 
23 Inflorescences at most loosely 10-flowered; inflorescence stalks shorter than or only slightly surpassing leaves
A. vexilliflexus var. vexilliflexus
23 Inflorescences usually more than 10-flowered; inflorescence stalks longer than leaves
A. eucosmus