What this is

Milkweed USA profiles 70 of the roughly 73 Asclepias species native to North America, together with 2 naturalised relatives that monarchs also use, with identification characters, generalized state-level ranges, cultivation notes and monarch guidance. It exists because the information gardeners need is scattered across academic floras, agency databases and forum threads, and rarely answers the two questions that matter: does this belong where I live, and how do I grow it.

Where the data comes from

• Distribution. Generalised to state level from the USDA PLANTS Database and the Biota of North America Program county maps.
• Taxonomy and nomenclature. Flora of North America and Plants of the World Online.
• Cultivation and germination. Regional native plant societies, Cooperative Extension publications and the practical literature on prairie restoration.
• Monarch ecology. The peer-reviewed literature on monarch host use, OE prevalence and migration, together with Monarch Watch, the Monarch Joint Venture and the Xerces Society.

Photographs

Every photograph on this site comes from Wikimedia Commons, filtered to licenses that permit commercial reuse: public domain, CC0, CC BY and CC BY-SA. NonCommercial and NoDerivatives files are rejected by the script that gathers them. Each photograph carries its photographer, its license and a link to the Commons file page, which is what those licenses require.

Photographs are downloaded and hosted here rather than linked from someone else's server, so they cannot break when a remote file moves, and the pages do not depend on anyone else's uptime.

Commons does not hold a usable photograph of every species. Where it does not, the page falls back to the plate described below.

The plates

Alongside the photographs, each species carries a diagnostic plate drawn programmatically from that species' own recorded characters: leaf shape, leaf arrangement, plant habit, mature height, flower color and hood color. A plate is a schematic summary of what separates one species from another, not a picture of one individual plant, and it exists for every species including the obscure ones nobody has photographed.

The trade-off is worth stating plainly. A plate will help you narrow a plant to two or three candidates. It will not replace a photograph or a herbarium specimen for a difficult determination.

Limits

• State-level ranges are coarse. A species listed for your state may occur only in three counties at the far end of it.
• Editorial ratings for garden value, monarch value and nectar value are judgements, not measurements.
• Nothing here is veterinary, medical or legal advice. For suspected poisoning contact a vet or poison control; for rare species law, contact your state natural heritage program.
• Rare and protected species are described so that people can recognize and report them, not collect them.

Corrections

Range errors, identification mistakes and outdated names are all worth reporting. Regional botanists know their floras better than any national compilation, and this guide improves when they say so.

Organisations worth supporting

• Monarch Watch for tagging, waystation certification and milkweed distribution.
• The Xerces Society for invertebrate conservation and regional milkweed seed initiatives.
• Monarch Joint Venture for habitat, monitoring and research coordination.
• Your state native plant society, which runs the plant sales worth going to.