Key to Asclepias

View taxon page for Asclepias

(For a list of species in Asclepias, use the above link.)

Jepson Manual glossary definitions can be seen by moving your cursor over words underlined with dots.

1. Leaves ephemeral (stem generally leafless), narrow-linear

2. Hoods exceeded by anther 

head 

1. A dense, often spheric inflorescence of sessile or subsessile flowers.
2. In Asteraceae and some other groups, a head-like inflorescence is one in which sessile or subsessile inflorescence units (e.g., heads in Asteraceae, umbels enclosed by involucres in Eriogonum), instead of individual flowers, are attached in a short dense cluster without an evident axis or branches.

..... A. albicans

2' Hoods much exceeding anther head ..... A. subulata

1' Leaves persistent, narrow-linear to wide-ovate or -elliptic

3. Leaves 1 per 

node 

Position on a stem from which one or more structures (especially leaves, buds, branches, or flowers) arise.

(alternate or subwhorled) ..... A. asperula subsp. asperula

3' Leaves > 1 per node (opposite or whorled)

4. Horn 0 or 

included 

Not protruding out of surrounding structure(s) (e.g., stamens included in corolla).

in hood

5. Hoods not or ± exceeded by anther head

6. Leaf 

sessile 

Without a petiole, peduncle, pedicel, or other kind of stalk.

, 

blade 

Expanded portion of a leaf, petal, or other structure, generally flat but sometimes rolled, cylindric, wavy, or cupped.

base clasping stem; corolla dark red-purple ..... A. cordifolia

6' Leaf short-petioled or sessile, blade base rarely clasping stem; corolla green-yellow or white

7. Leaf ± 

cordate 

Heart-shaped; often pertaining to a leaf in which the blade base on both sides of the petiole is rounded and convex.

or 

ovate 

Egg-shaped (i.e., widest below the middle) in two dimensions (i.e., in one plane), as a leaf.

to ± round; corolla green-yellow, 

lobes 

1. A major expansion or bulge, such as on the margin of a leaf, sepal, or petal, or on the surface of an ovary. 2. The free tips of otherwise fused structures, such as sepals or petals; larger than teeth.

10–15 mm; fruit glabrous, prickles 0 ..... A. cryptoceras

7' Leaf 

linear 

Elongate, with nearly parallel sides; narrower than elliptic or oblong.

or narrow- to oblong-lanceolate, 

acuminate 

Having a long-tapered, sharp tip, the sides concave.

; corolla white, lobes 7–8 mm; fruit 

puberulent 

Minutely hairy.

, with thread-like prickles ..... [A. fruticosa]

5' Hoods exceeded by anther head

8. Stem 

decumbent 

lying mostly flat on the ground but with tips curving up.

to ± 

ascending 

Curving or angling upward from base, or about 30-60 degrees less than vertical or away from axis of attachment.

; plant dense-hairy, ± white (appearing woolly at arm's length); tops of hoods exceeding base of anther head (hoods, anther head overlapped) ..... A. californica

8' Stem 

prostrate 

Lying flat on the ground.

(and ± flat); plant ± hairy, green (appearing glabrous at arm's length); tops of hoods exceeded by base of anther head (hoods, anther head not overlapped) ..... A. solanoana

4' Horn 

exserted 

Protruding out of surrounding structure(s) (e.g., stamens exserted from corolla).

from hood

9. Horn generally exceeding hood ..... A. fascicularis

9' Horn at ± same level as to much exceeded by hood

10. Hoods exceeding anther head by at least 1/2 their lengths

11. Hoods at ± same level as exserted horns, ± 

erect 

Upright; vertically oriented.

, tips rounded ..... A. nyctaginifolia

11' Hoods much exceeding exserted horns, ± ascending, tips 

acute 

Having a short-tapered, sharp tip, the sides convex or straight and converging at less than a right angle.

..... A. speciosa

10' Hoods not exceeding anther head by at least 1/2 their lengths

12. Inflorescences at 

nodes 

Position on a stem from which one or more structures (especially leaves, buds, branches, or flowers) arise.

sessile or nearly so ..... A. vestita

12' Inflorescences at nodes peduncled

13. Leaves generally broad-elliptic, rarely 

lanceolate 

Narrowly elongate, widest in the basal half, often tapered to an acute tip.

to ovate, tip 

obtuse 

Having a short-tapered, blunt tip or base, the sides convex or straight and converging at more than a right angle.

to 

truncate 

Abruptly (not gradually) narrower or smaller at base or tip, as if cut straight across or nearly so.

or notched. (Extirpated) ..... A. latifolia

13' Leaves 

elliptic 

In the shape of a flattened circle or ellipse; wider than linear

, lanceolate, or ovate, tip obtuse to acuminate

14. Leaves 

opposite 

1. Arranged in pairs along an axis - e.g., two leaves per node. 2. Occurring in the same rank, directly above or below, as 'stamens opposite petals'. 3. Located directly across from.

or 

whorled 

Arranged in groups of three or more at nodes or positions along an axis (e.g., three leaves per node).

, short-petioled to sessile, blade bases 

tapered 

Gradually (not abruptly) narrower or smaller at base or tip.

to obtuse, rarely cordate, margins generally not wavy, generally 

entire 

Having margins that are continuous and smooth (i.e., without teeth, lobes, etc.).

; hoods exceeded by to at ± same level as anther head; seed 8–9 mm ..... A. eriocarpa

14' Leaves opposite, generally sessile, blade bases tapered to cordate, margins generally ± wavy and/or ± jagged; hoods ± exceeding anther head; seed 10–13 mm ..... A. erosa

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