Asclepias tuberosa L. - Butterfly Milkweed

Asclepias tuberosa plant

Family - Asclepiadaceae

Stems - To +/-60cm tall, erect or ascending, herbaceous, hirsute and also with vertical lines of hairs from leaf bases, (the hairs small and curled), typically simple but branching near apex, from a woody crown.

Asclepias tuberosa stem

Leaves - Mostly alternate but sometimes opposite by inflorescence, dense on the stems, short-petiolate. Petioles to 3mm long. Blades linear-oblong to linear-lanceolate, entire, acute, truncate at the base, often with slightly revolute margins, pubescent above, more so below, green above, lighter green below, to 10cm long, +/-2.5cm broad.

Asclepias tuberosa leaves

Inflorescence - Terminal and axillary umbellate cymes with +/-25 flowers. Pedicels subtended by linear bracts to 1cm long, 1.2mm broad. Pedicels +/-2cm long, with antrorse pubescence, light green.

Asclepias tuberosa inflorescence

Flowers - Petals 5, orange, reflexed, 8-9mm long, 2.2mm broad, glabrous, acute. Hoods orange, glabrous, 5-6mm long, 1.5mm broad, distinct. Horns to 3mm long, orange. Column 3mm long(tall), greenish. Pollinia 2mm long, translator deep purple. Pistils 2, 2.1mm long, with a few antrorse hairs at apex. Follicles erect, to 15cm long, 1.5cm wide, pubescent. Seeds oval, to +5mm long, with coma.

Asclepias tuberosa flowersFlowers close-up.

Flowering - May - September.

Habitat - Prairies, glades, open woods, disturbed sites, waste ground, roadsides, railroads. Also cultivated.

Origin - Native to U.S.

Other info. - This plant is used much by gardeners wishing to attract butterflies to the area. The flowers produced copious amounts of nectar and the plant itself is eaten by the larva of Monarchs (Danaus plexippus) which indeed belong to the group of butterflies known as the "Milkweed Butterflies", family Danaidae. The butterflies store the cardiac glycosides produced by the plant and hence become distasteful and even dangerous to predators.
Asclepias tuberosa is the only species of the genus in Missouri not to have the milky white juice so commonly associated with the genus.
The subspecies most commonly found in this state is subsp. interior Woods., pictured above, which has leaves which are mostly cordate at the base. This subspecies has two forms. The red-flowered from (shown above) is form interior. Form lutea has yellow flowers and is rare in the state. This striking form is shown below:

Asclepias tuberosa yellow

Photographs taken off Hwy 106, Shannon County, MO., 6-6-03 and at Devil's Well, MO., 6-27-03, and off County Road 2010, Lawrence County, MO., 6-16-05.