Flowering in dappled sunlight to medium shade with curiously interesting white flowers,  Asclepias exaltata brightens up any woodland or shade garden.  It's commonly known as "The Poke Milkweed" for its resemblance to Phytolacca americana,  "Pokeweed".   The flowers are long lasting and weep down from atop 36" - 60" tall plants.  After fertilization,  the flowers fade and 6" to 10" vertical seed pods are set that persist all Summer and well into Autumn. These seeds are easy to collect and germinate.  I like to collect them as soon as the first pods start to split open at the seams.  At this point,  it's easy to scrape them from their silky parachutes before they're dispersed into the air.

The genus name Asclepias is derived from the Greek name of Aesculapius,  an ancient god of medicine. The common name "Milkweed" is for the milky sap that flows from a snapped stem in most species. In this species,  the specific epithet exaltata refers to the tall height of the plants.

"Milkweeds" are very popular butterfly attractors.  Asclepias exaltata attracts Silver-spotted Skippers, Pearl Crescents, Cloudywings, Great Spangled Fritillaries and Tiger Swallowtails to name a few.

There's a great closeup of the flowers of Asclepias exaltata at: http://www.ionxchange.com/species%20pages/a/asclepias_exaltata.htm

It seems that a naturally occurring hybrid exists between the "Common Milkweed",  Asclepias syriaca, and Asclepias exaltata, there's a picture of it at: http://www.carolinabutterflysociety.org/june302001.htm

Taxonomic Hierarchy
Kingdom - Plantae - Plants
Subkingdom - Tracheobionta - Vascular plants
Superdivision -  Spermatophyta - Seed plants
Division - Magnoliophyta - Flowering plants
Class - Liliopsida - Monocotyledons
Subclass - Asteridae
Order - Gentianales
Family - Asclepiadaceae
Genus - Asclepias
Species - exaltata
Common name - genus -  "Milkweed"
Common name - species - "Poke Milkweed"
Synonyms - A. phytolaccoides
Native range - See - http://plants.usda.gov/cgi_bin/topics.cgi
USDA Hardiness Zone - 5, maybe 4
Light preference -  Open bright shade
Soil fertility preference -    Average to rich
Soil pH preference - neutral to slightly acidic
Soil moisture preference - Average to moist,  not wet
Bloom time -  Mid Spring to early Summer
Bloom color - White
Foliage -  Dark green
Spread - 12" - 24"
Height - 36" - 60"
Deer palatability - Seems deerproof
Landscape uses - Specimen or colonial plantings in the shade garden, butterfly garden
Related species - Many species of "Milkweed"
Medicinal uses - See: http://www.botanical.com/botanical/mgmh/a/ascle072.html