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Key to families | Table of families and genera

Specimen numbers are hyperlinked to records in the Consortium of California Herbaria data view where possible. Taxa are hyperlinked to entries in the Jepson Interchange via the "[Online Interchange]" link.

 

ASCLEPIAS MILKWEED

Thomas J. Rosatti & Carol A. Hoffman


Annual, perennial herb, shrub. Stem: prostrate to erect. Leaf: generally opposite (alternate, whorled), each pair at right angles to those below, above, generally persistent; blade narrow-linear to ovate or cordate. Inflorescence: terminal or at generally upper nodes, umbel-like cyme. Flower: ring of tissue at base of corolla 0; filament column appendages (hoods) free, elevated above corolla base or not, each often with an elongate projection (horn) attached to inside, margins converging and meeting or nearly meeting adaxially but not fused; anthers fused into anther head around and fused to pistil head, pollen in pollinia; pistil head flat or conic on top; nectaries in stigmatic chambers. Fruit: erect (but generally on pendent pedicel) or pendent, lance-ovoid to ovoid, smooth or with tubercles.
In narrow sense of genus, 100 species: North America, Central America, perhaps South America. (Greek physician Aesculapius) Fresh flowers generally better for determining relative positions of parts; hoods may have near anther head 2 ± sickle shaped lobes each that may ± resemble horns. A. linaria not outside cultivation in California, so deleted here; previous inclusion in TJM2 (2012) based on faulty locality data.
Unabridged references: [Liede-Schumann & Meve 2006 http://www.uni-bayreuth.de/departments/planta2/research/databases/delta_as/www/asclep.htm; Woodson 1954 Ann Missouri Bot Gard 41:1–211]

Key to Asclepias

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

2. Hoods exceeded by anther head ..... 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 (alternate or subwhorled) ..... A. asperula subsp. asperula

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

4. Horn 0 or included in hood

5. Hoods not or ± exceeded by anther head

6. Leaf sessile, blade 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 or ovate to ± round; corolla green-yellow, lobes 10–15 mm; fruit glabrous, prickles 0 ..... A. cryptoceras

7' Leaf linear or narrow- to oblong-lanceolate, acuminate; corolla white, lobes 7–8 mm; fruit puberulent, with thread-like prickles ..... [A. fruticosa]

5' Hoods exceeded by anther head

8. Stem decumbent to ± ascending; 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 (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 from hood

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

9a. Filament column ± 2 mm; leaves opposite, without clusters of smaller leaves in axils; corolla bright crimson, rarely yellow or white ..... [A. curassavica]

9a' Filament column ± 1 mm; leaves opposite (and reduced, on sterile branches) or whorled, often with clusters of smaller leaves in axils; corolla green-white, purple-tinged or not ..... 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, tips rounded ..... A. nyctaginifolia

11' Hoods much exceeding exserted horns, ± ascending, tips acute ..... A. speciosa

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

12. Inflorescences at nodes sessile or nearly so ..... A. vestita

12' Inflorescences at nodes peduncled

13. Leaves generally broad-elliptic, rarely lanceolate to ovate, tip obtuse to truncate or notched. (Extirpated) ..... A. latifolia

13' Leaves elliptic, lanceolate, or ovate, tip acute to acuminate

14. Leaves opposite or whorled, short-petioled to sessile, blade bases tapered to obtuse, rarely cordate, margins generally not wavy, generally entire; 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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Citation for the whole project: Jepson Flora Project (eds.) [year] Jepson eFlora, http://ucjeps.berkeley.edu/IJM.html [accessed on month, day, year]
Citation for an individual treatment: [Author of taxon treatment] [year]. [Taxon name] in Jepson Flora Project (eds.) Jepson eFlora, [URL for treatment]. Accessed on [month, day, year].
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