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Key to Asclepias

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1 Sap clear; leaves alternate; corolla orange to yellow
1 Sap milky (the milkiness often difficult to show in A. verticillata, which has numerous, whorled, linear leaves); leaves strictly or primarily opposite, subopposite, or whorled; corolla orange, red, white, cream, green, pink, or purple.
..2 Leaves lanceolate, ovate, or elliptic, 1-5 (-10)× as long as wide.
....3 Leaves sessile, subsessile, or with petioles to 3 mm long
....3 Leaves with petioles (3-) 4-20 mm long.

Key to Asclepias, Key A: milkweeds with clear sap and alternate leaves

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1 Leaves ca. 2× as long as wide; leaf base truncate to subcordate; leaf apex broadly rounded and also often notched; [of c. FL scrub]
1 Leaves > 3× as long as wide; leaf base cordate, subcordate, truncate, rounded, or cuneate; leaf apex acuminate, acute or obtuse; [collectively widespread].
..2 Leaves > 9× as long as wide, widest near the base; leaf base broadly cuneate to truncate; apex acuminate; [e. TX and e. OK westwards and southwestwards]
..2 Leaves 3-8× as long as wide, widest near the base, near the middle, or towards the apex (or the margins parallel for >3/4 of the leaf length); leaf base cordate, subcordate, truncate, rounded, or cuneate; leaf apex acuminate, acute, or obtuse; [collectively widespread].
....3 Leaves widest near the base; leaf base cordate, subcordate, or truncate, with well-developed basal lobes broader than a 'waist' above; [PA, WV, KY, TN, and AL westwards]
....3 Leaves widest above the midpoint, near the midpoint, or with margins nearly parallel for > 3/4 of the leaf length; leaf base subcordate, truncate, rounded, or cuneate; [IN, s. IL, AR, and e. TX eastwards].
......4 Leaf base cuneate, rounded, or truncate; leaves widest above the middle or near the midpoint; [s. NH west to OH, south to Panhandle FL and e. TX widespread eastwards]
......4 Leaf base truncate or subcordate; leaves either widest above the midpoint, above a waist created by hastate basal lobes, or with margins nearly parallel for > 3/4 of the leaf length; [of se. Coastal Plain, se. VA south to s. FL, west to s. MS]

Key to Asclepias, Key B: milkweeds with milky sap, with linear leaves opposite, subopposite, or whorled

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1 Leaves either mostly in whorls of 3-6 (sometimes some nodes with merely opposite leaves), or subopposite (the leaves more-or-less paired but separated by 0.5-3 mm); corolla whitish or greenish, usually suffused with rose-purple (especially at the tips of the corolla lobes).
..2 Leaves mostly in whorls of 3-6 (sometimes some nodes with merely opposite leaves); leaves 1.5-7 cm long, 0.5-2 mm wide; seeds ca. 5 mm long, the coma ca. 2.5 cm long; milky sap often difficult to show
..2 Leaves subopposite (the leaves more-or-less paired but separated by 0.5-3 mm); leaves (3-) 5-18 cm long, (1-) 2-10 mm wide; seeds 7-11 mm long, the coma 3-5 cm long; milky sap obvious and profuse.
....3 Umbel 1, terminal; corona 5-7 mm in diameter; horns present, about as long as the hood; hoods ca. 2-4 mm long, surpassing the anther heads; [dry pinelands of the Coastal Plain]
....3 Umbels 1-4, terminal and from upper nodes; corona 2-3 mm in diameter; horns absent; hoods ca. 2 mm long, surpassed by the anther heads; [either wet pinelands of the Coastal Plain or dry glades or woodlands].
......4 Pedicels with spreading hairs; umbels 2-10, each with up to 30-100 flowers; leaves minutely scabrous; [dry glades or woodlands, known from the Mountains of nw. GA, e. TN, w. WV westward]
......4 Pedicels with incurved hairs; umbels 1-6, each with 10-30 flowers; leaves glabrous or nearly so; [wet pinelands of the Coastal Plain]
1 Leaves opposite; corolla white, whitish, or greenish, usually suffused with rose-purple (especially at the tips of the corolla lobes), or creamy yellow, purple, or orange-red.
........5 Corolla lobes erect (vertical), creamy yellow to dull or greenish white, 7-10 mm long; leaves 2.5-4.5 cm long, puberulent beneath, sessile; corolla lobes erect, creamy yellow to dull or greenish white, 7-10 mm long; plant 1-4 dm tall; [dryish pinelands of the Coastal Plain]
........5 Corolla lobes reflexed to spreading, either orange-red, with at least some purple, or whitish or greenish, 3-7 mm long (except 8-11 mm long in the orange-red A. lanceolata); leaves 5-20 cm long, glabrous or glabrate beneath (rarely puberulent), sessile to petiolate; plant 1-15 dm tall; [collectively of various habitats].
..........6 Leaves with petioles 1-10 mm long; leaves 5-15 mm wide; plants 5-15 dm tall.
............ 7 Petiole 4-10 mm long; corolla pink (rarely white), the lobes 3-5.5 mm long; hoods 1-2 mm long; horns longer than the hoods; [mostly of the Mountains and Piedmont]
............ 7 Petiole 1-3 mm long; corolla orange-red, the lobes 8-11 mm long; hoods 5-6 mm long; horns slightly shorter than the hoods; [of the Coastal Plain]
..........6 Leaves sessile, subsessile (with petioles 0-1 mm long); leaves 1-7 mm wide; plants 1-7 dm tall.
............ ..8 Leaves 1-2 mm wide.
............ ....9 Pedicels ca. 2 cm long, arching, the flowers often nodding; horns present (somewhat longer than the hood); hoods with 2 erect, acuminate, marginal teeth on the inner side (adjoining the anther heads); corolla ashy-gray, pale violet, or pale rose; [se. NC (historically) and e. SC south to n. peninsular FL, west to s. MS]
............ ....9 Pedicels 1-1.5 cm long, ascending, the flowers facing upwards; horns absent or present; hoods lacking marginal auricles; corolla white, pale pink, or green (and often suffused with purple); [se. GA and s. AL south to s. FL]
............ ......10 Corolla white or pale pink; hoods shorter than the gynostegium; horns absent
............ ......10 Corolla green to cream, often suffused with purple; hoods longer than the gynostegium; horns present
............ ..8 Leaves 3-7 mm wide.
............ ........11 Umbel 1, terminal; corona 5-7 mm in diameter; horns present, about as long as the hood; hoods ca. 2-4 mm long, surpassing the anther heads; [dry pinelands]
............ ........11 Umbels 1-10, terminal and from upper nodes; corona 2-3 mm in diameter; horns absent; hoods ca. 2 mm long, surpassed by the anther heads; [either of wet pinelands of the Coastal Plain or dry glades or woodlands].
............ ..........12 Pedicels with spreading hairs; umbels 2-10, each with up to 30-100 flowers; leaves minutely scabrous; [dry glades or woodlands, east to nw. GA, TN, and WV]
............ ..........12 Pedicels with incurved hairs; umbels 1-6, each with 10-30 flowers; leaves glabrous or nearly so; [wet pinelands of the Coastal Plain]

Key to Asclepias, Key C: milkweeds with milky sap, with sessile, nonlinear leaves

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1 Leaves 2-5 cm long, 0.3-1.0 cm wide; corolla lobes erect, creamy yellow to greenish white, 7-10 mm long; plant 1-4 dm tall; [of dryish pinelands of the Coastal Plain, e. NC to s. FL, west to FL Panhandle]
1 Leaves 3-30 cm long, 0.5-11 cm wide (not simultaneously < 5 cm long and < 1 cm wide); corolla lobes reflexed, either orange-red, purple, pink, greenish-yellow, or green, 5-15 mm long; plant 2-10 dm tall; [collectively widespread].
..2 Leaves cordate-clasping at base, 3-10 cm wide, 1-2.5× as long as wide; stem and leaves glabrous and usually also glaucous; flowers primarily pink-colored.
....3 Plant prostrate or decumbent; leaves blue-green with conspicuous pink veins throughout; inflorescence usually with numerous axillary umbels present (occasionally plants with a solitary terminal umbel); [dry pinelands of the southeastern coastal plain; NC to FL, w. to e. LA]
....3 Plant erect, not falling over and laying on the ground; leaves green, not blue-tinted, with pink midribs but lacking conspicuous secondary or tertiary pink veins; umbels solitary and terminal or with a few umbels concentrated terminally or in the upper most leaf axils; [collectively widespread]
......4 Leaves usually spreading (although also sometimes upright or oriented dowmward), with strongly undulate margins; peduncles long, the terminal umbel usually strongly exerted past the upper leaves; [widespread in our region]
......4 Leaves usually ascending, without (or with only slightly) undulate margins; peduncles short, slightly exerted, the terminal umbels usually not surpassing the upper-most leaves; [south to sc. OH, s. IN, s. IL, MO, and OK]
..2 Leaves cuneate, rounded, or cordate at base; rarely cordate-clasping; 1-6 cm wide, (1-) 1.5-6× as long as wide; stem and leaves pubescent to glabrate (or glabrous in A. meadii); flowers cream, green, or pink-colored (if pink colored then leaves lanceolate and acuminate-tipped).
........5 Corolla lobes 12-15 mm long, greenish-yellow (sometimes suffused with some purple); flowers 3-6 (-8) per umbel; hoods strongly inward-arching over the gynostegium, almost touching at their tips.
........5 Corolla lobes 6-9 mm long, reddish-purple, pink, pale green, or greenish-yellow; flowers > 7 per umbel; hoods erect, or slightly spreading at their tips.
..........6 Leaves lanceolate, acuminate at the apex; corolla reddish purple to pink, the lobes 7-9 mm long; [of wetlands, Coastal Plain and very rarely inland]
............ 7 Flowers primarily green-colored; plants usually with solitary terminal umbels nodding; [upland prairies; rare from s. MO and s. IL n. to nw. IN and sw. IA]
............ 7 Flowers primarily pink-colored; plants often with more than one umbel and usually oriented upright; [wet habitats and seepages of the Coastal Plain; NJ to FL, w. to TX]
..........6 Leaves orbicular to oblong, rounded at the apex; corolla pale green (sometimes suffused with some purple), the lobes 6-7 mm long; [of dry habitats, widespread]
............ ..8 Hood with a narrowly falcate horn, sometimes suffused pink, margins of the hood strongly curved inward, conspicuous; corolla lobes usually flaring outward
............ ..8 Hood without a horn, sometimes suffused purple, all portions of the hood strongly appressed, somewhat inconspicuous (not curved inward marginally); corolla lobes strongly reflexed, appressed to the pedicel

Key to Asclepias, Key D: milkweeds with milky sap, with petiolate, nonlinear leaves, in flower

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1 Corolla (not the corona) greenish, either pale green or yellowish green.
..2 Leaves subopposite (to alternate upwards); corolla lobes 7-17 mm long.
....3 Corolla lobes 7-12 mm long; leaves mostly 4-7× as long as wide, acuminate at the apex; [e. OK and e. TX and westwards]
....3 Corolla lobes 13-17 mm long; leaves mostly 2-4× as long as wide, obtuse at the apex; [c. TX and c. OK and eastwards]
..2 Leaves opposite; corolla lobes 6-10 mm long.
......4 Corona 2-3 mm across; corolla lobes pale green, 5-7 mm long; [of various provinces, Coastal Plain and also especially inland]
........5 Corolla lobes reflexed-rotate; corona white to pink, with purple markings; [ne. FL to s. peninsular FL]
........5 Corolla lobes strongly reflexed, appressed to the pedicel; corona green, white, or yellowish, with purple markings; [widespread in our area, but not ne. FL and peninsular FL]
......4 Corona 5-9 mm across; corolla lobes yellowish green, 9-10 mm long; [strictly of the Coastal Plain, of NC and SC, and southward].
..........6 Hoods ca. 6 mm long, about 2× as long as the gynostegium; stem and leaves densely tomentulose
..........6 Hoods ca. 4 mm long, scarcely exceeding the gynostegium; stem and leaves softly puberulent
1 Corolla (NOT the corona) pink, purple, crimson, orange, or white.
............ 7 Hoods about as long as the anther heads; horns 1-2× as long as the hood, exserted slightly to well beyond the hood.
............ ..8 Hood opening truncate, the hood therefore beaker-shaped; corolla lobes 8-12 mm long; [primarily of mesic forests of the Mountains]
............ ..8 Hood opening very oblique, the hood therefore scoop-shaped; corolla lobes 2.5-10 mm long; [primarily of wetlands of various provinces].
............ ....9 Corolla bright orangey red, the lobes 5-10 mm long; corona orangey yellow; gynostegium orangey yellow
............ ....9 Corolla white, pink, rose, or purple, the lobes 2.5-6 mm long; corona white, pink, or rose; gynostegium white or pale pink.
............ ......10 Plants 3-5 dm tall; corolla lobes usually white (rarely slightly pink); corona white; leaves glabrous beneath; [of the Coastal Plain of SC]
............ ......10 Plants 5-15 dm tall; corolla lobes rose to purple (rarely white); corona pink or rose; leaves pubescent to glabrate beneath; [collectively widespread].
............ ........11 Stems and leaves sparsely pubescent to glabrescent; leaves narrow, the base obtuse to truncate, the apex long-acuminate; plants usually much branched
............ ........11 Stems and leaves moderately to densely pubescent; leaves broader, the base rounded to subcordate, the apex acute to short-acuminate; plants usually relatively strict
............ 7 Hoods distinctly longer than the anther heads; horns 0.5-1× as long as the hood, not conspicuously exserted beyond the hood.
............ ..........12 Lower leaf surface pubescent over the surface.
............ ............ 13 Hood margin irregular but not with a sharp tooth; corolla purplish-rose; plants 4-10 dm tall
............ ............ 13 Hood margin with a single, ascending, triangular tooth; corolla rose or greenish-white; plants (5-) 8-20 dm tall
............ ..........12 Lower leaf surface glabrous to sparsely pubescent along the midvein only.
............ ............ ..14 Hood opening very oblique, the hood therefore scoop-shaped, and also with 2 prominent lateral teeth; corolla pink to greenish (rarely white); plants 2-5 dm tall
............ ............ ..14 Hood opening truncate and constricted, and lacking prominent teeth; corolla white (often pink at the "waist"); plants 3-12 dm tall

Key to Asclepias, Key E: milkweeds with milky sap, with petiolate, nonlinear leaves, in fruit (or sterile)

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1 Leaves subopposite
1 Leaves opposite (or apparently whorled in A. quadrifolia).
..2 Follicle pendant; seeds without a coma; [of swamp forests of SC and southward]
..2 Follicle erect; seeds with a coma; [collectively widespread].
....3 Leaf-bearing nodes 3-4, the upper and lower opposite, the middle with a whorl of 4 leaves
....3 Leaf-bearing nodes 3-many, all opposite.
......4 Follicle slightly to strongly muricate
......4 Follicle smooth.
........5 Lower leaf surface glabrous, or pubescent on the midrib only
..........6 Leaves 1-3 cm wide; follicles 6-10 cm long
..........6 Leaves 3-11 cm wide; follicles 12-14 cm long
........5 Lower leaf surface pubescent.
............ 7 Leaves lanceolate, 4-10× as long as wide.
............ ..8 Leaves coriaceous, 3-10 cm long, 1.5-4.5 cm wide; [of dry upland situations]
............ ..8 Leaves herbaceous, 6-15 cm long, 2-7 cm wide; [of moist to wetland situations].
............ ....9 Stems and leaves sparsely pubescent to glabrescent; leaves narrow, the base obtuse to truncate, the apex long-acuminate; plants usually much branched
............ ....9 Stems and leaves moderately to densely pubescent; leaves broader, the base rounded to subcordate, the apex acute to short-acuminate; plants usually relatively strict
............ 7 Leaves ovate to elliptic, 1.5-4× as long as wide.
............ ......10 Stem moderately to densely pubescent; plants 1.5-5 (-7) dm tall; [of xeric pinelands of the Coastal Plain of from NC to s. FL, west to OK, AR, and TX].
............ ........11 Stem and leaves densely tomentulose; leaves mucronate
............ ........11 Stem and leaves softly puberulent; leaves apiculate
............ ......10 Stem glabrous to pubescent in lines only; plants 2-12 dm tall; [collectively of various habitats throughout our area].
............ ..........12 Lower leaf surface densely puberulent; [primarily of moist to wet habitats]
............ ..........12 Lower leaf surface glabrous or slightly pubescent; [of moist or dry habitats].
............ ............ 13 Leaves 4-9 cm wide, acuminate at the apex
............ ............ 13 Leaves 1-6 cm wide, mostly obtuse at the apex.
............ ............ ..14 Leaves with subcordate, truncate, or broadly rounded bases; [ne. FL to s. peninsular FL]
............ ............ ..14 Leaves with cuneate or rounded bases; [widespread in our area, but not ne. FL and peninsular FL]
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