four-leaved milkweed (Asclepias quadrifolia)
SCIENTIFIC SYNONYMS: There are no scientific synonyms for
CONFIRMATION STATUS: Pending confirmation.
TAXONOMY: The currently accepted scientific name for four-leaved
milkweed is Asclepias quadrifolia Jacq.
NATIVE STATUS: Native, United States and Canada.
GENERAL BOTANICAL CHARACTERISTICS:
Habit: Four-leaved milkweed is an erect, slender, simple, herbaceous,
from rhizomes, perennial, woodland plant and one of the smallest in the
Milkweed (Asclepiadaceae) Family. It typically grows a single, unbranch-
ed stem from a long and fleshy rootstock, with the stem growing 1 to 2.5
feet. The stem is purplish at the base and apex, with one flat side, mostly
glabrous but with hairs in distinct vertical lines on margins of flat side ex-
tending down from leaf bases, with milky sap.
Leaves: Leaf arrangement is in opposite pairs with two pairs separated by
a short internode, giving the appearance of being in a whorl of four (often
referred as a false whorl). Upper leaves are paired, thin (1/2 to 2.8 inches
wide), egg to lance-shaped, entire, with curly hairs on veins on both sur-
faces, 2 to 6 inches long with long-pointed tips. A pair of leaves typically
subtend the inflorescence. Stalks are 1/5 to 4/5 inch long.
Flowers: Flowers are arranged terminally in upper leaf axils, with one to
four umbels, each containing 5 to 25 (sometimes more) small, pinkish-
white flowers. Flower stalks thread-like, 1/5 to 1.6 inch long and are mi-
nutely pubescent. There are 5 calyx lobes, lanceolate to ovate, green to
purplish, smooth, without hairs. There are also 5 corolla lobes corolla
lobes 5, elliptic-lanceolate, 1/5 to 1/4 inch long, pale pink to pinkish-
white, bent abruptly downward. Hoods are narrowly oblong, about 1/6
inch long, white to pinkish tinged, attached near bases, spreading, with
prominent lateral teeth above base. The horns are short, flattened, sickle-
shaped, curved inward, attached to lower 1/2 of hood. Two pistils are
green, about 2 mm long, and smooth, without hairs. There are many
Fruit/Seeds: Seeds are borne in a pod which is slender, 3.2 to 5.6 inches
long, 1/4 to 1/3 thick, minutely-hairy to smooth, usually with 20 to 35
brown, flattened, teardrop-shaped seeds per pod. To aid in dispersal, the
seeds have dense tufts of long, silky white hairs at the top. Mature plants
produce one or two, rarely three, pods per plant.
Roots: Insufficient information.
REGENERATION PROCESS: Four-leaved milkweed propogates itself
by reseeding. Fourleaved milkweed is threated in several regions of the
United States and Canada (where it occurs in small, isolated populations
in southern Ontario). Research suggests several reasons why this particular
milkweed is not thriving; three of the most important and consistent reasons
1) Milkweed is relatively slow to mature, estimating that plants do not pro-
duce seed until at least from 5 to 10 years depending on resources such as
soil depth, moisture and sunlight.
2) Plants reproduce only from seed, not vegetatively. This means four-
leaved is vulnerable to factors that limit sexual reproduction such as herb-
ivory, late frosts, or lack of pollinators.
Pollinator dependency is based mainly on bees and butterflies. Four-
leaved milkweed is not pollinated by wind or animals. Reductions in pol-
linator species could limit plant reproduction; studies have found more
than 50% of insects carrying pollinaria were of one species. In general,
research studies have found very low rates of pollination four-leaved milk-
HABITAT TYPES: Four-leaved milkweed naturally occurs in dry open
woods and thickets, generally on upland slopes and ridges, often with
rocky, chert soils. Can also be found in some disturbed areas, such along roadsides.
SITE CHARACTERISTICS: Four-leaved milkweed prefers shade to
partial sun, and typically occur on dry to mesic, shallow or rocky soils
over limestone or, sometimes sandstone, bedrock on or near steep slopes
within a semi-open, mature deciduous forest, usually comprised of oak
and hickory. Soil characteristics typically found are gravel and rock, but
it also grows in loamy and clay situations.
SEASONAL DEVELOPMENT: Four-leaved milkweed generally
blooms from late spring to early summer (April into July).
GENERAL DISTRIBUTION: Four-leaved milkweed naturally occurs
throughout most of the eastern United States, ranging from Georgia north
into Vermont and New Hampshire, and extending west to the Mississippi
River states into Oklahoma and Kansas and north to Minnesota. It also
occurs in Ontario, Canada. It generally does not occur in the Gulf Coast
region, the southwest, upper Plains states or Provinces, or the far west
and northwest states or provinces.
SKY MEADOWS DISTRIBUTION: To be determined.
IMPORTANCE AND USES: Four-leaved milkweed is attractive to many
insects because of the copious amounts of nectar produced by the flowers
(although not all are effective pollinators). As many as 22 species of insects
have been observed carrying four-leaved milkweed pollin, virtually all of
which were species of Hymenoptera (bees and wasps) and Lepidoptera
(butterflies, moths and skippers). Of the six major potential pollinators, the
main species was a bee, Melissodes desponsa (Hymenoptera). The five
other major species were skippers (family Hesperiidae) – Zabulon skipper
(Poanes zabulon), hobomok skipper (Poanes hobomok), tawny-edged
skipper (Polites themistocles) and Peck’s skipper (Polites coras/Polites
peckius) and a Nymphalid butterfly – pearl crescent (Phyciodes tharos).
Other species of bees and butterflies are known pollinators of a similar
species of milkweed (see following entry for swamp milkweed for a more
comprehensive discussion of importance and uses).
Native Americans used an infusion of the root to treat backaches and
venereal disease. They also used the plant as a laxative, rubbed it on warts
to remove them, and used fibers from the plant to make bowstrings.
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