milkweeds

genus Asclepias

Member of milkweeds (subfamily Asclepiadoideae)
dogbane family (family Apocynaceae)
dicots (class Magnoliopsida)
flowering plants (subphylum Angiospermae)

Except for old historical records and extremely rare examples that I don't expect to encounter, there are no other wild species of this genus in the bay area.

The petals and sepals are reflexed, revealing the gynostegium, which is a blunt plug composed of fused stamens and styles. The gymnostegium is surrounded by five hoods, each (at least partially) hiding a horn.

A labeled photo of the milkweed flower parts.

Key features for all local milkweeds:

visible hood and horn characteristics
inflorescence sessile or with peduncle

california milkweed
Asclepias californica

hoods closed at top
horns hidden
leaves opposite; petiole short to 0; blade ovate
rare in east bay and south bay

woollypod milkweed
Asclepias eriocarpa

hoods closed at top
horns barely peeking out to ± height of hood and gymnostegium
hoods not exceeding anther tip by at least ½ their lengths
inflorescences at nodes peduncled
leaves opposite or whorled in 3s or 4s; petiole short to 0; blade elliptic, lanceolate, or ovate, base tapered to obtuse (to cordate), tip obtuse to short-acuminate, margins generally not wavy, generally entire
not confirmed in the bay area?

narrowleaf milkweed
Asclepias fascicularis

hoods open at top
horns sticking out above hood and gymnostegium
leaves opposite or whorled generally in 3s to 5s, often with clusters of smaller leaves in axils; petiole short; blade narrow-lanceolate, base tapered
common, but not west of Skyline Blvd.

woolly milkweed
Asclepias vestita

hoods open at top, short (not exceeding anther tip by at least ½ their lengths)
horn exserted from hood, at ± same level as to much exceeded by hood
inflorescences at nodes sessile or nearly so
Pinnacles

showy milkweed
Asclepias speciosa

hoods open at top, very long (exceeding anther tip by at least ½ their lengths)
horn exserted from hood
Mt. Tam, Briones, Los Trampas

Toxicity of indian paint brush, milkweed (Asclepias spp.):
4 – Ingestion of these plants, especially in large amounts, is expected to cause serious effects to the heart, liver, kidneys or brain. If ingested in any amount, call the poison center immediately.

3 observed taxons / 2 unobserved taxons / 1 key

Chris’s observations: 14 (13 are research grade)

Locations:

Coyote Lake / Harvey Bear Ranch CP: 5
Almaden Quicksilver CP
Dimond Canyon Trail, Oakland
Dry Creek Pioneer RP
Ed R. Levin CP
Edgewood Park & Natural Preserve
Henry Coe SP
Mission Peak RP
Pinnacles NP
Ulistac Natural Area, Santa Clara

Months:

Apr.: 2
May: 1
Jun.: 6
Jul.: 4
Aug.: 0
Sep.: 0
Oct.: 1

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Not all sites include this taxon:

genus Asclepias → iNaturalist – Calflora – Jepson eFlora
not yet listed → FNA

Bay Area species: iNaturalist – Calflora