Asclepias cordifolia

Asclepias cordifolia (Heartleaf Milkweed)

1. Identity and Botanical Classification

Scientific and Common Names

Asclepias cordifolia (Benth.) Jeps. is the currently accepted binomial name for this species. It belongs to the family Apocynaceae, subfamily Asclepiadoideae, tribe Asclepiadeae, subtribe Asclepiadinae, within the genus Asclepias. The species was originally described by George Bentham as Acerates cordifolia Benth. and later combined into the genus Asclepias by Willis Linn Jepson, whose authority abbreviation "Jeps." follows the accepted name in formal nomenclature. Additional historical synonyms include Gomphocarpus cordifolius (Benth.) Benth. ex A.Gray.

Common names include Heartleaf milkweed and Purple milkweed, the latter not to be confused with Asclepias purpurascens, which shares this vernacular name. The USDA Plants Database registers this species under the symbol ASCO.

The species name cordifolia is Latin for "heart-leaved," referring to the heart-shaped leaves, while the genus name Asclepias honors the Greek physician Asclepius.

Morphology

Heartleaf milkweed is a perennial that grows to a height of 0.3–0.6 meter, with dark red-purple flowers. The plant has an opposite leaf arrangement; leaves are clasping, large heart-shaped or lance-shaped, and bluish-green with a purplish tinge, measuring 4–7 inches (10–18 cm) in length. Leaves bear short hairs, are sessile and clasp the stem; the floral hoods are open at the top and the inner side. Blooms appear in clusters that are slightly fragrant, with a maroon and white coloration. Bloom colors range from red to purple, and flowering occurs from May through July. Fruit is a follicle containing many seeds, each with a tuft of silky white hairs adapted for wind dispersal.

The genus Asclepias, commonly known as milkweed, consists of herbaceous perennial flowering plants belonging to the dogbane family Apocynaceae (formerly classified in Asclepiadaceae), which also includes oleander, hoya, and plumeria. The Asclepias genus contains over 200 species distributed broadly across Africa, North America, and South America.

Natural Distribution and Habitat

Heartleaf milkweed is native to the western United States — California, Nevada, and Oregon — growing at elevations between 50 and 2,000 meters in the northern Sierra Nevada and Cascade ranges. Its native habitat encompasses woodland and coniferous forests, but it is most commonly found on rocky slopes. It requires coarse to medium soils and grows well in rocky ground. It is the smallest of the commonly cultivated California milkweeds, growing 1 to 2 feet tall and approximately 1 foot wide.

Relationship to the Broader Asclepias Genus and Supplementary Context

Carl Linnaeus named the plant genus Asclepias (then containing approximately 130 milkweed species) after the Greek god of healing, Asklēpiós, son of Apollo, because of its long use as a medicinal group of plants. Members of the genus are named for their latex — a milky substance containing cardiac glycosides termed cardenolides — which exudes where cells are damaged. It is critical to note at the outset that Asclepias cordifolia specifically is not registered as a dietary supplement ingredient in any regulatory database (including the U.S. FDA Dietary Supplement Ingredient Advisory List or NIH Office of Dietary Supplements databases), and no clinical trials specific to this species appear in PubMed or other major scientific literature databases. The information that follows therefore contextualizes A. cordifolia within the ethnobotanical record of the genus and the phytochemical science of Asclepias species broadly, clearly identifying which data relate specifically to A. cordifolia and which apply to the wider genus.

2. Traditional and Historical Use

Fiber and Material Culture Uses

The most thoroughly documented ethnobotanical uses of Asclepias cordifolia are not medicinal but technological. The Miwok people of northern California used heartleaf milkweed for its stems, which they dried and used for cords, strings, and ropes. The Miwok gathered heartleaf milkweed in the summer and dried it, or collected it in the autumn after it was already dry. The dry stems were combed with a loop of willow to draw out the fiber just beneath the very thin outer skin. The fiber was wound into balls for storage and later processing. The making of cordage — rope and string — was done entirely by hand, with no tools.

The scale of this industry is reflected in the ethnographic record. A single Miwok feather skirt or cape required approximately 100 feet of cordage from about 500 plant stalks, while a 40-foot-long deer net required approximately 7,000 feet of cordage and the harvesting of an estimated 35,000 plant stalks. Heartleaf milkweed was also used by the Native American Yokuts (or Mariposa) of northern and central California for string or rope.

Broadly across the genus, milkweed has been used for fiber, food, and medicine all over the United States and southern Canada. Fibers from milkweed stems have been identified in prehistoric textiles in the Pueblo region. Tewa-speaking people of the Rio Grande still make string and rope from these fibers, and at Zuni the silky seed fibers are spun on a hand-held wooden spindle and made into yarn and woven into fabric, especially for dancers.

General Ethnobotanical Medicinal Use Within the Genus

While the specific documented uses of A. cordifolia in the ethnobotanical record are primarily fiber-based, related species within the Asclepias genus have a long history of medicinal use among North American Indigenous peoples. Milkweeds have a long history of medicinal, everyday, and military use. The Omaha people of Nebraska, the Menominee of Wisconsin and upper Michigan, the Dakota of Minnesota, and the Ponca of Nebraska traditionally used common milkweed (A. syriaca) for medicinal purposes. Several species of the genus have been used by people from many cultures around the world to treat ailments concerning the cardiac, digestive, and respiratory systems.

The USDA National Plant Data Center's Plant Guide for Asclepias cordifolia carries an explicit warning: milkweed may be toxic when taken internally without sufficient preparation. No documented, specific medicinal preparation or application of A. cordifolia itself by any named Indigenous group has been confirmed in the reviewed literature; the species' ethnobotanical role appears to have been overwhelmingly as a fiber plant rather than a medicinal one. Claims of medicinal internal use for A. cordifolia specifically should therefore not be extrapolated from the broader genus record without explicit source documentation.

Ecological Cultural Uses

Many milkweed species contain cardiac glycoside poisons that inhibit animal cells from maintaining a proper potassium and calcium concentration gradient, and as a result, many peoples of South America and Africa used arrows poisoned with these glycosides to fight and hunt more effectively. However, this use relates to different species and continents and cannot be attributed to A. cordifolia specifically.

3. Key Constituents and Phytochemistry

Cardenolides (Cardiac Glycosides)

The genus Asclepias is characterized by its latex, which contains cardiac glycosides termed cardenolides. Most species are toxic to humans and many other species, primarily due to the presence of cardenolides. Cardiac glycosides are a large class of secondary metabolites found in plants; in the genus Asclepias, cardenolides have an established role in plant-herbivore and predator-prey interactions, based on their ability to inhibit the membrane-bound Na⁺/K⁺-ATPase enzyme.

Cardenolides consist of a steroid backbone, an unsaturated lactone, and glycoside moieties. Single species of Asclepias can contain up to 21 different cardenolides, and both compound diversity and concentration are variable among tissues. Cardenolide defenses in milkweeds can vary in terms of the total concentration, differences in the polarity of individual cardenolides, and the substitution of the steroidal structures that contribute to the molecule's reactivity.

Typically among Asclepias, there is a trans configuration of rings A and B in the steroidal skeleton — different from the cis configuration found in cardenolides from other plant genera — and a cyclic bridge to a single sugar moiety. Cardenolides also vary in structural sugar groups (the "glycoside" of cardiac glycosides) that conjugate to core aglycone steroidal structures; this can alter the chemical properties of the molecule. Cardenolides can also have reactive moieties such as aldehydes that form hydrogen bonds between the molecule and the Na⁺/K⁺-ATPase. Sugars in cyclic bridges, such as a dioxane ring, are highly resistant to acid hydrolysis. Not all cardenolides are therefore equally toxic to herbivores.

No peer-reviewed phytochemical analysis isolating and characterizing individual compounds specifically from Asclepias cordifolia was identified in the literature search. Phytochemical profiles documented for closely related California milkweed species, such as A. eriocarpa, include varying seasonal and intraplant concentrations of cardenolides, but species-specific data on A. cordifolia's exact cardenolide profile are not available in the current reviewed literature.

Latex and Other Constituents

The milky white sap that oozes from the broken stems and leaves of many types of milkweed is a latex that contains high concentrations of steroid derivatives called cardenolides, specifically cardiac glycosides. Milkweed sap also contains other compounds — alkaloids and proteolytic enzymes — that can irritate skin and mucous membranes. Milkweed latex contains about two percent latex material; during World War II both Nazi Germany and the U.S. attempted to use it as a source of natural rubber, although no record of large-scale success has been found.

Monarch butterfly caterpillars eat the Heartleaf milkweed leaves, which contain alkaloids that cause the butterfly to be unpalatable to predators. Even after the caterpillar has metamorphosed into a butterfly, the alkaloids ingested from the plant are retained in the butterfly, making it unpalatable to predators.

Seed Floss

Milkweed floss — the silky material attached to seeds — can be used in thermal and acoustic insulation. It is highly buoyant and water-repellent, but absorbs oil readily, making it potentially useful for oil spill cleanup. The fine, silky fluff attached to milkweed seeds, which allows them to be distributed long distances on the wind, is known as floss. Milkweed floss is incredibly difficult to spin due to how short and smooth the filaments are, but blending it with as little as 25% wool or other fiber can produce workable yarn. These uses apply to the genus broadly and are not specific to A. cordifolia.

4. Mechanisms of Action of Cardenolides

Cardenolides are toxic to animals through inhibition of the enzyme Na⁺/K⁺-ATPase, which is responsible for maintaining the sodium and potassium ion gradients across cell membranes. Milkweeds contain various toxic cardenolides that have cardiotoxic effects; the cardenolides act by inhibiting Na⁺/K⁺-ATPase, thereby affecting myocardial conduction and contractility.

Cardiac glycosides disrupt proper muscle (including heart) and kidney function, the nervous system, and the body's acid-base balance. The cardenolides interfere with sodium-potassium ATPase in animal cells; this disruption alters heart muscle contractility and can cause arrhythmias at sufficient doses.

In addition to the cardiotoxic effects of cardenolides common to most milkweeds, other glycosides and resinoids identified in milkweeds have direct effects on the respiratory, digestive, and nervous systems, causing dyspnea, colic, diarrhea, muscle tremors, seizures, and head pressing.

Because it contains cardenolides, Asclepias can have digitalis-like effects and potentiate digitalis toxicity. Interference with assays of plasma digoxin concentrations is also possible.

Research into the pharmacological potential of cardenolides from related species (primarily A. curassavica) has explored their Na⁺/K⁺-ATPase-inhibitory properties in the context of cardiotonic activity. The cardiac effects of asclepin, a cardenolide glycoside from Asclepias curassavica, were studied in vitro (isolated guinea pig atrium and heart) and in vivo (anesthetized cat); asclepin showed a marked positive inotropic effect as evidenced by an increase in the force of contraction, and was found to be more active than the reference glycosides g-strophanthin, digoxin, digitoxin, and digitoxigenin. This research pertains to A. curassavica, not A. cordifolia.

5. Scientific Evidence: Areas of Claimed or Potential Activity

Absence of Clinical Evidence for Asclepias cordifolia Specifically

A systematic search of PubMed, PMC, and related scientific databases reveals no published human clinical trials, randomized controlled trials, systematic reviews, or even substantial observational studies evaluating Asclepias cordifolia as a dietary supplement, medicinal preparation, or therapeutic agent. No NIH Office of Dietary Supplements monograph, WHO monograph, ESCOP monograph, German Commission E monograph, or European Pharmacopoeia entry exists for this species. Asclepias cordifolia is therefore entirely absent from the formal evidence base for dietary supplements. The sections below describe what is known about the genus for context, clearly noting the species to which each finding actually applies.

Cardiovascular / Cardiotonic Activity (Genus-Level; Preclinical Only)

Within the genus, research interest in cardenolides' cardiotonic properties mirrors the pharmacological interest historically associated with digitalis glycosides. In a preclinical study of asclepin (from A. curassavica), the compound demonstrated a marked positive inotropic effect in isolated guinea pig heart preparations and in vivo in anesthetized cats. This pharmacodynamic activity reflects the general mechanism by which all cardenolides function — Na⁺/K⁺-ATPase inhibition leading to increased intracellular calcium and enhanced myocardial contractility — and carries the same therapeutic-to-toxic ratio concerns that have shaped the clinical use of digitalis. No human evidence from any Asclepias species supports cardiovascular benefit at any defined supplemental dose; all evidence is preclinical and from related species, not from A. cordifolia.

Potential Anticancer Activity (Genus-Level; In Vitro Only)

Cardenolide glycosides from various Asclepias species have been investigated in cell culture (in vitro) settings for antiproliferative activity. Studies of A. subulata extracts reported antiproliferative and apoptotic activity against cancer cell lines. Studies of related Apocynaceae members (such as Calotropis gigantea) found that cardenolides including uscharidin and calotropin showed cytotoxic effects at low nanomolar concentrations, with associated G2/M cell cycle arrest. These findings are all in vitro, species-specific, and conducted with related but distinct taxa — not Asclepias cordifolia. No animal or human studies of anticancer activity from A. cordifolia have been reported. Evidence strength: preclinical only (in vitro), cannot be extrapolated to clinical efficacy.

Summary of Evidence Strength

For Asclepias cordifolia specifically, there is no published clinical, animal, or substantive in vitro evidence of efficacy for any health indication. The species has not been evaluated in controlled human studies for any purpose. The broader genus has generated preclinical data on cardenolide pharmacology, but the same compounds responsible for any theoretical pharmacological activity are also the primary source of documented toxicity (see Safety section below). The current body of evidence does not support characterizing A. cordifolia as a safe or effective dietary supplement for any indication.

6. Body Systems and Health Areas Associated with the Genus

Based on the phytochemistry of the genus broadly, Asclepias species have historically been associated with the following body systems — though again, these associations are supported only at the genus or related-species level, not specifically for A. cordifolia, and carry established toxicity risks:

• Cardiovascular system: Several species of the genus have been used by people from many cultures to treat ailments concerning the cardiac system. Cardenolides directly affect Na⁺/K⁺-ATPase in cardiac muscle cells.
• Digestive/gastrointestinal system: Glycosides and resinoids in milkweeds have direct effects on the digestive system, capable of causing colic and diarrhea. Traditional food uses of Asclepias pods and shoots (primarily A. syriaca) required specific preparation to reduce toxicity.
• Respiratory system: Milkweed constituents have been associated with effects on the respiratory system, including dyspnea.
• Nervous system: Milkweed resinoids can affect the nervous system, causing muscle tremors and seizures.
• Integumentary system (skin and eyes): Corneal injury and defects have been documented from direct contact of milkweed sap to the eye, and any exposure should be immediately treated with copious water irrigation. Latex irritants in the sticky white sap — containing proteins and secondary metabolites — can cause dermatitis and eye irritation.

7. Dosage Forms and Reported Dosages

No dosage has been established or reported in the scientific or regulatory literature for Asclepias cordifolia as a dietary supplement or medicinal preparation in humans. The species has not been formulated into any commercially registered supplement or evaluated in dose-ranging clinical studies. The following contextual observations from the genus are provided for reference only and do not represent recommended doses:

• Cardenolides in Asclepias species are active at extremely low concentrations. Related compounds (e.g., digoxin) have narrow therapeutic windows in humans, with toxicity occurring at concentrations only slightly above therapeutic levels.
• Lethal doses of cardenolides in livestock occur at approximately 2% of body weight with fresh milkweed and 0.05% of body weight with dried milkweed. These are toxicological reference points for livestock, not human supplemental dosing guidance.
• Traditional fiber processing of A. cordifolia involved the stems only, which were dried — a method that does not constitute a medicinal preparation or dosing regimen.

In the absence of any established safe dosage, and in light of documented cardenolide toxicity, no dose of A. cordifolia material for internal consumption can be characterized as established, safe, or effective based on current evidence.

8. Safety Considerations and Toxicology

General Toxicity of the Species

The Calflora database, a California botanical authority, explicitly advises "Do not eat any part of this plant" in reference to Asclepias cordifolia. The USDA NRCS Plant Guide for A. cordifolia also carries a warning that milkweed may be toxic when taken internally without sufficient preparation.

Most Asclepias species are toxic to humans and many other species, primarily due to the presence of cardenolides. The level of toxicity varies dramatically among species and plant parts. Milkweeds are most toxic during rapid growth and retain their toxicity even when dried in hay.

Human Toxicology

Ingestion of plants containing cardioactive steroids has resulted in detectable digoxin concentrations, toxicity, and even death. A 2013 case reported a 42-year-old man experiencing cardiac symptoms and nausea after consuming fried milkweed pods; in the emergency department, he was found to have a heart rate in the 40s and a digoxin level of 1.0 ng/mL (cross-reactivity of the assay). Symptoms of milkweed poisoning may include abdominal discomfort, nausea, vomiting, diarrhea, weakness, lethargy, and confusion, progressing to seizures, heart rhythm changes, and bradycardia.

Milkweed contains cardenolides concentrated in the milky latex; symptoms from ingestion usually begin with gastrointestinal upset, while large ingestions can affect the heart and nervous system.

Dermal and Ocular Toxicity

The sticky white sap, containing proteins and secondary metabolites, can cause dermatitis and eye irritation. Corneal injury and defects have been documented from direct contact of milkweed sap with the eye, and any such exposure should be immediately treated with copious water irrigation.

Livestock Toxicity

While horses and other equines are most at risk for milkweed poisoning, all animals including chickens, cattle, sheep, dogs, cats, and even humans, as well as some insects, are susceptible to milkweed toxins. Sheep and goats are the most susceptible to poisoning as they prefer to browse on weedy species; ingestion usually occurs with overgrazing or hay contamination. All milkweeds are poisonous to some degree to all classes of livestock including poultry; poisoning is not uncommon in sheep and cattle, and occurs occasionally in horses, goats, alpacas, and rabbits.

Drug Interactions

Because Asclepias species contain cardenolides, they can have digitalis-like effects and potentiate digitalis toxicity. Interference with assays of plasma digoxin concentrations is also possible. Any concurrent use of cardiac medications — particularly digoxin, antiarrhythmics, or other cardioactive agents — alongside milkweed-derived preparations would carry pharmacodynamic interaction risk based on the shared Na⁺/K⁺-ATPase inhibition mechanism. This concern is pharmacologically well-grounded at the genus level, though not specifically tested with A. cordifolia extracts in human subjects.

Treatment of Poisoning

There is no specific treatment for milkweed poisoning. Management is supportive. Animals that consume a sublethal dose should recover within a few days; if an animal is known to have consumed milkweed, it should be moved from the plant source, given fresh water, good quality hay, and shelter. In humans, the clinical approach parallels management of cardiac glycoside toxicity generally.

9. Ecological Significance and Conservation Context

A noteworthy feeder on milkweeds is the monarch butterfly, which uses and requires certain milkweeds as host plants for its larvae. Monarch butterfly caterpillars eat the Heartleaf milkweed leaves, which contain alkaloids that cause the butterfly to be unpalatable to predators. In a phylogenetic study of 49 Asclepias species for geographic clines in cardenolide production, it was found that Asclepias species from tropical regions are better defended by cardenolides than more temperate species. Heartleaf milkweed is noted as an important plant for monarch conservation in California and serves as a host plant for multiple pollinator species. Its ecological value as a native California plant is well established, even as its potential for human internal use remains unsupported and potentially hazardous.

10. Summary and Conclusions

Asclepias cordifolia is a botanically well-characterized perennial herb native to the western United States, belonging to a medically historically significant genus. Its documented uses in the ethnobotanical record are primarily material-cultural: the Miwok, Yokuts, and related California tribes valued its stem fibers for cordage production, not for internal medicinal use. The genus Asclepias broadly carries a long history of medicinal application by North American Indigenous peoples, but species-specific medicinal use of A. cordifolia is not established in the reviewed literature.

The plant's primary active compounds — cardenolide cardiac glycosides — are well characterized at the genus level and function as Na⁺/K⁺-ATPase inhibitors. These compounds are responsible for both the pharmacological interest in the genus (cardiotonic activity, preclinical anticancer studies) and its documented toxicity in humans and animals. For Asclepias cordifolia specifically, no species-specific phytochemical profile has been published in peer-reviewed literature, no clinical trials have been conducted, no established safe dosage exists, and no regulatory body has recognized it as a dietary supplement ingredient. Multiple authoritative botanical sources explicitly warn against ingesting any part of the plant. The evidence base, in summary, does not support characterizing A. cordifolia as a dietary supplement; its primary documented relationships to human use are fiber-based (historical, traditional) and toxicological.

References

• Calflora: Asclepias cordifolia (Benth.) Jeps. — Taxon Page
• Calscape (CNPS): Heartleaf Milkweed — Asclepias cordifolia
• Lady Bird Johnson Wildflower Center: Asclepias cordifolia (Heartleaf milkweed)
• USDA NRCS National Plant Data Center: Plant Guide for Asclepias cordifolia
• Wikipedia: Asclepias cordifolia
• Wikipedia: Asclepias (genus)
• Wikispecies: Asclepias cordifolia — Taxonomy and Synonymy
• Rubiano-Buitrago P, et al. (2022). New Structures, Spectrometric Quantification, and Inhibitory Properties of Cardenolides from Asclepias curassavica Seeds. Molecules. PMC9822358.
• Agrawal AA, et al. (2012). Toxic cardenolides: chemical ecology and coevolution of specialized plant–herbivore interactions. New Phytologist. 194(1):28–45.
• PNAS (2021): Cardenolides, toxicity, and the costs of sequestration in the coevolutionary interaction between monarchs and milkweeds.
• ScienceDirect: Asclepias — Encyclopedia of Toxicology (overview)
• Colorado State University Guide to Poisonous Plants: Milkweed (Asclepias spp.)
• University of Wisconsin Extension: Milkweed and Milkweed Toxicity
• University of Illinois Extension / ERC: Milkweed Toxicity to Livestock — Management Recommendations
• Colorado State University Extension: Managing Western Whorled Milkweed
• ACEP Now: Toxicology Answer — Milkweed (Asclepias)
• PubMed: Pharmacological investigation on asclepin — a new cardenolide from Asclepias curassavica. PMID 380581.
• CNPS Jepson Chapter: Asclepias spp. — Plant of the Month (February 2021)
• U.S. Fish & Wildlife Service: Spreading Milkweed, Not Myths
• Frontiers in Ecology and Evolution (2023): Differential accumulation of cardenolides from Asclepias curassavica by large milkweed bugs.