Asclepias hirtella (Pennell) Woodson

Prairie Milkweed

Asclepias hirtella plant

Family - Asclepiadaceae

Habit - Perennial herb from thickened woody rootstock.

Stems - Ascending to erect, to 1.1 m, densely pubescent in upper half, mostly unbranched, with numerous nodes, with milky sap.

Asclepias hirtella plantStem and nodes.

Leaves - Alternate, occasionally subopposite, sessile or short-petiolate. Leaf blades 4-17 cm long, 0.3-1.5 cm wide, narrowly lanceolate, entire, the base narrowed or tapered, the tip tapered gradually to a sharp point, the margins flat, sparsely to moderately rough-pubescent with short, stiff hairs, especially along the veins and margins. Margins thickened and often reddish.

Asclepias hirtella stem2Stem and leaves.

Asclepias hirtella leaf1Leaf adaxial.

Asclepias hirtella leaf2Leaf abaxial.

Inflorescences - Axillary umbels, usually 2-10 per stem, short-stalked or sometimes appearing sessile, with 25-90 flowers. Peduncles and pedicels densely pubescent. Pedicels to 1.5 cm long in flower. Umbels subtended by linear bracts to 6 mm long. Bracts pubescent.

Asclepias hirtella inflorescence2Inflorescences.

Asclepias hirtella inflorescenceInflorescence.

Flowers - Calyx lobes 5, reflexed, hairy, 1.5-3.0 mm long, lanceolate to ovate. Corolla lobes 5, reflexed, glabrous, pale green, usually with purple spots or tinting, the lobes 4-6 mm long, elliptic-lanceolate. Gynostegium appearing stalked (the column visible below the bases of the hoods), pale green, the corona noticeably shorter than the tip of the anther/stigma head. Corona hoods 1.5-2.5 mm long, erect, attached most of their length, oblong-elliptic in outline, the opening oriented toward the column, the tips broadly rounded to truncate, the margins not toothed, the bases pouched, whitish with purple tint at base. Horns absent. Carpels 2, 2.1 mm long, glabrous.

Asclepias hirtella flowerFlower.

Asclepias hirtella flowersFlowers and friend.

Fruits - Follicles 7-14 cm long, erect or ascending from usually deflexed stalks, lanceolate to narrowly ovate in outline, the surface smooth, minutely hairy. Seeds with the body 7-9 mm long, the margins relatively broadly winged, the terminal tuft of hairs white or more commonly light tan, to 3 cm.

Asclepias hirtella fruitsFruits.

Flowering - May - August.

Habitat - Prairies, glades, and pastures.

Origin - Native to U.S.

Other info. - Even though its flowers are mostly white, this may still be one of the showiest milkweeds in Missouri. There are usually multiple inflorescences, which can have a brilliant, shining aspect. The plant occurs throughout much of Missouri but is uncommon or absent from most of the southeastern third of the state. It is easy to identify when flowering, with multiple light inflorescences and numerous narrow leaves. This is a striking species worthy of more widespread cultivation.

Photographs taken off Hwy 126, Barton County, MO., 7-4-03, and in Wayne Fitzgerrell State Park, IL., 8-3-05 (DETenaglia); also at Taum Sauk State Park, Iron County, MO, 8-23-2009 and 9-8-2014 (SRTurner).


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