Notes on Asclepias species identification

Notes on Asclepias species identification

This page last modified on 26 November, 2005

Jepson key and descriptions pg 171-172

Main distinction between the three species known to grow in the right areas is the length and/or presence of the "horns", and the height of both horns and "hoods" relative to the top of the "anther head" (illustrated in Jepson drawing on pg 191). The extent to which the plant is "hairy" or "glabrous" (i.e lacking hairs) is also significant.

In A.californica, the horns are either missing, or out of sight inside the "hoods", and the hoods don't quite reach top of the anther head. Plant densely hairy
In A.eriocarpa, the horn is exserted from the hood, and may extend roughly to the tip of the hood. Corolla reflexed to ascending, cream-colored or sometimes tinged pink. Plant very hairy (sometimes becoming less so.)
In A.fascicularis the horn is exserted from and extends beyond the hood. Corolla greenish to pale yellow, sometimes tinged purple. Plant generally glabrous.

Beauchamp pg 87 describes A.eriocarpa as "frequent", and the other two as "occasional". Three other Asclepias species found in San Diego county occur only in the desert areas.

Asclepias californica - California/Round-hood Milkweed
These flowers don't show the horns, and the hoods don't quite reach up to the top of the anther head. The flower heads are densely hairy, but the leaves are at most just fuzzy, or have sparsely distributed appressed hairs.

Asclepias eriocarpa - Indian Milkweed
These flowers have horns that extend well beyond the hoods, and reach the edge of the top of the anther head. The flower heads are obviously hairy. The leaves look fuzzy (more-so than those I've labelled A.californica), but if hairy then the hairs are very short.

Asclepias fascicularis - Narrow-leaf Milkweed
These flowers have horns that extend beyond the hoods and reach the edge of the top of the anther head. The exteriors of the corolla lobes (as seen on the still unopened buds) are mostly glabrous. The leaves are almost completely glabrous (i.e smooth surface, not hairy).

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