The Southwest's Rarest Milkweed

In this episode, we arrive at perhaps one of the most intriguing and vivid habitats we have visited yet - coral-pink sand dunes comprised of weathered, 150 million year old Navajo Sandstone to document a flora that includes one of the rarest milkweeds on Planet Earth - Asclepias welshii.

Homo sapiens may be driving the world to our own specialized version of hell at the moment, but things were calm and quiet here on the Colorado Plateau yesterday. These pink sand dunes are the largest of the 8 known populations of the rare and federally-listed milkweed, Asclepias welshii. It forms large clonal colonies here in the more open and exposed areas of the dunes. It's proximal leaves nearer the stem are smooth and glabrous, but the distal leaves nearer the spherical inflorescences are covered in a thick layer of wool that picks up the orange-ish pink sand grains, weathered out of the Jurassic Navajo sandstone.


Asclepias welshii wasn't even described until 1979, based on herbarium specimens collected by Holmgren twenty years prior. It has the largest seeds of any milkweed, only 5 mm shy of an inch long (2 cm), and seeds can last in the shifting sands for years. The roots of this plant must go deep down into the dune beds. The first year seedlings have leaves that look remarkably different from adult plants - linear and narrow. The other populations are East of this one, two or three of them on Navajo land. The flowers are aromatic and smell a bit like vanilla.

Species list for this episode :

#Penstemon laevis (Plantaginaceae)
Hymenopappus filifolius (Asteraceae)
Eriogonum alatum (Polygonaceae)
#Scabrethia scabra
#Sophora stenophylla (Fabaceae)
Ladeania lanceolata (Fabaceae)
Comandra umbellata (Sanatalaceae)
#Asclepias welshii (Apocynaceae)

Much thanks to Blake Wellard for help keying out a few of these taxa down to species (ie Penstemon laevis and Ladeania lanceolata).

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