Asclepias perennis Walt. - Perennial Milkweed

Asclepias perennis plant

Family - Asclepiadaceae

Stems - Multiple from a woody crown, erect to ascending, herbaceous, glabrescent below, with a longitudinal line of antrorse hairs in the internodes above, to +40cm tall, typically simple, terete to somewhat compressed.

Asclepias perennis stem

Leaves - Opposite, petiolate, typically about 6-8 pairs below the inflorescence. Petioles to +1.5cm long, with an adaxial groove formed by decurrent blade tissue, glabrous. Blades narrowly elliptic to elliptic-lanceolate, dull green above, light-green below, essentially glabrous except for a few antrorse hairs on the midrib below, entire, acute to acuminate, to +12cm long, +2cm broad. Midrib impressed adaxially, expressed abaxially.

Asclepias perennis leaves

Inflorescence - Pedunculate umbels from the upper leaf axils with +/-25 flowers per umbel. Lower peduncles longer than the upper thus creating a flat-topped inflorescence. Peduncles to +2cm long, pubescent. Rays of inflorescence subtended by linear bracts. Bracts 2-4mm long, -1mm broad, sparse pubescent. Rays sparse antrorse pubescent, +1cm long, light purplish to greenish.

Asclepias perennis inflorescence

Flowers - Petals 5, white, spreading with the tips slightly incurved, 3-4mm long, +/-2mm broad, elliptic, sub-acute at the apex. Hoods white, glabrous, -2mm long. Horns white, exserted from the hoods for +2mm and arched over the anther column. Anther column light-purple, 2mm tall, 1.5mm in diameter, white at the apex. Pollinia total length 1.5mm long. Pollen sacs 1mm long. Terminator dark purple. Pistils 2, glabrous, green, enclosed by and subtending the anther column. Sepals 5, alternating with the petals, light-green, linear to linear-lanceolate, -3mm long, -1mm broad, sub-acute. Fruits not seen.

Asclepias perennis flowers

Asclepias perennis flowerIndividual flower.

Flowering - Late May - September.

Habitat - Low, wet woods, cypress swamps, lake and pond margins, slow streams, wet ditches.

Origin - Native to U.S.

Other info. - This attractive species can be found only in the south-east corner on Missouri and is more common in states to the south and east. The plant can be identified by its many, mostly glabrous stems, elliptic, opposite leaves, and many clusters of small, white flowers. The only other white-flowered species of milkweed in Missouri are A. variegata L. and A. verticillata L. and neither resembles A. perennis.
Many species of Asclepias are harmful if ingested becasue they contain many cardiac glycosides and other secondary compounds. The sap from these plants should not be rubbed in the eyes or nose as it can be dangerous also.

Photographs taken off Hwy 65, Craighead County, AR., 6-12-05.


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