Flora of the Southeastern United States
2022 Edition

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Key to Fabaceae, Key K: herbaceous legumes with pinnately trifoliolate leaves [subfamily Faboideae]

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1 Leaflets denticulate (sometimes inconspicuously so); [tribe Trifolieae].
..2 Inflorescences elongate racemes with an axis 5-15 cm long, the flowers well-spaced along the axis, the overall inflorescence much longer than its diameter
..2 Inflorescences umbellate or headlike clusters or short racemes with an axis < 2 cm long, the flowers closely clustered, the overall inflorescence little (if at all) longer than its diameter.
....3 Legumes spirally coiled or curved, often tuberculate or prickly; stems 4-angled towards the tip
....3 Legumes straight or nearly so, never tuberculate or prickly; stems terete or flattened (2-angled) towards the tip
1 Leaflets entire (and sometimes also with 1 or 2 broad lobes), or with scattered, irregular large teeth (Pachyrhizus erosus).
......4 Main stems erect or ascending, not trailing, twining, or otherwise vine-like.
........5 Flowers not papilionaceous (the wings and keel epistemonous, arising terminally or laterally from the stamen tube), barely bilaterally symmetrical; stamens 5, monadelphous; [tribe Amorpheae]
........5 Flowers papilionaceous; stamens 10, diadelphous or monadelphous.
..........6 Plants with separate leafy and flowering stems (the flowering stems naked or nearly so of leaves).
............7 Standard bright red, remaining folded, 30-50 mm long; leaves hastately lobed; fruit a torulose legume, 6-20 cm long, the seeds red; [tribe Phaseoleae]
............7 Standard white or pink, expanded, 4-8 mm long; leaves not hastate; fruit a flattened loment, < 5 cm long, the seeds drab; [tribe Desmodieae]
..........6 Plants bearing leaves and flowers on the same stems.
..............8 Leaves, stems, and/or calyces glandular-punctate.
................9 Corollas pink or lavender/purplish; leaflets estipellate; fruit 1-seeded, indeciscent; [tribe Psoraleae]
................9 Corollas yellow; leaflets stipellate; fruit 2-many-seeded, dehiscent; [tribe Phaseoleae, subtribe Cajaninae]
..................10 Corollas 15-20 mm long; seeds 3-8 per fruit; fruit 4-9 cm long, constricted between each seed; [rare introduction]
..................10 Corollas 4-14 mm long; seeds 1-2 per fruit; fruit 1-2 cm long, with no constrictions, tapering to each end; [collectively common and widespread].
..............8 Leaves, stems, and calyces lacking punctate glands.
....................11 Leaflet blades large, at least the largest terminal leaflets on a plant > 5 cm long.
......................12 Stipels absent on the petiolules of mature leaflets; stamens monadelphous.
........................13 Fruit a legume (not segmented into 1-seed dispersal units), hairy but the hairs not hooked; [plants cultivated as garden plants, rare as waifs]
........................13 Fruit a loment (separating into single-seeded segments), uncinulate (with hooked hairs, the fruits attaching to hairs or clothes as 'stick-tights'); [plants widespread, common]
......................12 Stipels present, persistent; stamens diadelphous (9 and 1).
..........................14 Fruit a loment (separating into single-seeded segments), uncinulate (with hooked hairs, the fruits attaching to hairs or clothes as 'stick-tights'); [plants widespread, common]
..........................14 Fruit a legume (not segmented into 1-seed dispersal units), hairy but the hairs not hooked; [plants cultivated as crops or garden plants, rare as waifs]
............................15 Keel of corolla coiled 1-3 turns; stipules inconspicuous; [soy beans]
............................15 Keel of corolla not coiled; stipules conspicuous, persistent, striate; [bush green beans or lima beans]
....................11 Leaflet blades smaller, all on a plant < 5 cm long.
..............................16 Stipels present, persistent.
................................17 Fruit a loment (separating into single-seeded segments), uncinulate (with hooked hairs, the fruits attaching to hairs or clothes as 'stick-tights')
................................17 Fruit a several- to many-seeded legume, glabrous to hairy (but not uncinulate)
..............................16 Stipels absent on the petiolules of mature leaflets.
..................................18 Fruits dehiscent, a legume with 2 or more seeds.
....................................19 Terminal leaflet very similar in size as the 2 lateral leaflets; banner petal prominently striate-veined
....................................19 Terminal leaflet 2× or more as long as the 2 lateral leaflets; banner petal evenly colored
..................................18 Fruits indehiscent: either 1-seeded, or a loment with 2 or more one-seeded (indehiscent) segments.
......................................20 Petioles fused most of length with amplexicaul stipules, the leaves thus appearing sessile or nearly so; corollas lemon to orangy yellow; flowers subsessile; fruit a loment of 2 segments, the terminal segment fertile, the lower segment either sterile or fertile
......................................20 Petioles free from stipules, leaves evidently petiolate; corollas white to pink; flowers pedicellate; fruit either 1-seeded, or a loment normally with 3+ segments
........................................21 Fruit a loment, with 1-3 segments; terminal leaflets 3-10 cm long, 1-1.5× as long as wide; stamens monadelphous
........................................21 Fruit 1-seeded; terminal leaflets 1-5 cm long, 1.2-8× as long as wide; stamens diadelphous (9 and 1)
......4 Main stems trailing, twining, creeping, or climbing or sprawling over other vegetation.
..........................................22 Leaves, stems, and/or calyces glandular-punctate; corollas yellow.
..........................................22 Leaves, stems, and calyces lacking punctate glands; corollas yellow, pink, purplish, white, red, blue.
............................................23 Leaflet blades smaller, all on a plant < 5 cm long.
..............................................24 Stipels absent on the petiolules of mature leaflets.
................................................25 Fruit a loment of 2 segments, the terminal segment fertile, the lower segment either sterile or fertile; corollas lemon to orangy yellow
................................................25 Fruit 1-seeded; corollas pink-purplish to white, or bronze to brick-red.
..................................................26 Corollas pink-purplish to white
..................................................26 Corollas bronze to brick-red
..............................................24 Stipels present, persistent (minute in Amphicarpaea).
....................................................27 Fruit a loment (separating into single-seeded segments), uncinulate (with hooked hairs, the fruits attaching to hairs or clothes as 'stick-tights').
......................................................28 Flowers in axillary or terminal racemes; leaflets rotund, broadly ovate, broadly elliptic, or narrowly elliptic, the larger > 1 cm long.
......................................................28 Flowers in axillary clusters; leaflets broadly obovate, 0.5-1 cm long
....................................................27 Fruit a legume, dehiscent (at least tardily), unsegmented, and with 2+ seeds.
........................................................29 Flowers resupinate (the pedicel twisted 180 degrees), the banner 2.5-5.5 cm long and positioned lowermost.
..........................................................30 Calyx lobes equal to or longer than the calyx tube; fruits 3-5 mm wide
..........................................................30 Calyx lobes shorter than the calyx tube; fruits 5-8 mm wide
........................................................29 Flowers not resupinate, the banner 0.7-2.5 cm long and positioned uppermost.
............................................................31 Stipules caducous
............................................................31 Stipules persistent, sometimes conspicuous, sometimes striate.
..............................................................32 Keel petal and the included style straight to gently upcurved; stems very slender, < 0.75 mm in diameter
..............................................................32 Keel petal and the included style either strongly curved upwards 90-180 degrees, or even more extensively coiled (asymmetrically and spirally) in towards the flower center; stems slender to thicker, > 0.75 mm in diameter.
................................................................33 Keel petal and the included style strongly curved upwards 90-180 degrees; corollas yellow or pink to lavender (or whitish).
..................................................................34 Corollas pink to lavender (or whitish); corolla keel usually somewhat twisted, asymmetrical; [widespread in our region]
..................................................................34 Corollas yellow; corolla keel symmetrical; [mainly outer Coastal Plain]
................................................................33 Keel petal and the included style extensively coiled > 180 degrees (asymmetrically and spirally) in towards the flower center; corollas pink, purple, maroon, purple-black (or whitish).
....................................................................35 Peduncles long, the flowers borne in clusters on a raceme axis shorter than the peduncle; plants glabrate to villous, the hairs not hooked
....................................................................35 Peduncles short, the flowers scattered along a (sometimes branched) raceme axis, the raceme axis about as long as or longer than the peduncle; plants uncinulate pubescent (use 20× magnification, or touch the plant for the 'tacky' feel)
............................................23 Leaflet blades large, at least the largest terminal leaflets on a plant > 5 cm long.
......................................................................36 Stipels absent on the petiolules of mature leaflets; stamens monadelphous
......................................................................36 Stipels present, persistent (minute in Amphicarpaea); stamens diadelphous (9 and 1) or monadelphous (Pueraria).
........................................................................37 Stamens monadelphous; robust herbaceous vine with stems to 30 m long; flowers purple, when fresh smelling like artificial grape flavoring.
........................................................................37 Stamens diadelphous (9 and 1); herbacous vines with stems usually < 5 m long; flowers various in color, not 'grapy' in odor.
..........................................................................38 Flowers resupinate (the pedicel twisted 180 degrees), the banner (standard) petal lowermost; banner (standard) 25-50 mm long, much larger than the other petals.
............................................................................39 Calyx lobes equal to or longer than the calyx tube; fruits 3-5 mm wide
............................................................................39 Calyx lobes shorter than the calyx tube; fruits 5-8 mm wide
..........................................................................38 Flowers not resupinate, the banner (standard) uppermost; banner (standard) < 25 mm long, or if up to 30 mm then not much llonger than the other petals.
..............................................................................40 Fruit a loment (separating into single-seeded segments), uncinulate (with hooked hairs, the fruits attaching to hairs or clothes as 'stick-tights')
..............................................................................40 Fruit a several- to many-seeded legume, glabrous to hairy (but not uncinulate).
................................................................................41 Keel incurved < 90 (-120) degrees; style glabrous or pubescent.
..................................................................................42 Stipules inconspicuous or obsolescent.
....................................................................................43 Leaflets coarsely toothed; roots tuberous
....................................................................................43 Leaflets with entire margins (sometimes with 1-2 rounded lobes); roots slender
......................................................................................44 Corolla 3-4 cm long; fruits constricted between the seeds; fruits with stinging hairs
......................................................................................44 Corolla < 2 cm long; fruits constricted or not; fruits glabrous or hairy, the hairs not stinging.
........................................................................................45 Bracteoles below the calyx persistent; ventral suture of the fruit bumpy-nodose; style bearded
........................................................................................45 Bracteoles caducous; ventral suture of the fruit not bumpy-nodose; style glabrous.
..........................................................................................46 Leaflets (2-) 4-8 cm long, 0.8-1.5 cm wide, 5-6× as long as wide; leaflet apices acute to obtuse; fruits not flanged or winged
..........................................................................................46 Leaflets 6-14 cm long, 4-10 cm wide, 1-1.3× as long as wide; leaflet apices strongly acuminate; fruits with a flange or wing along the ventral suture
..................................................................................42 Stipules persistent and conspicuous.
............................................................................................47 Legume quadrangular in ×-section, 4-winged
............................................................................................47 Legume circular, elliptic, or oblong in ×-section, not winged.
..............................................................................................48 Flowers clustered 3 or more at the inflorescence nodes; upper calyx lobes fused.
..............................................................................................48 Flowers arrayed differently; upper calyx lobes separate.
................................................................................................49 Keel petal and the included style straight to gently upcurved; stems very slender, < 0.75 mm in diameter
................................................................................................49 Keel petal and the included style strongly curved upwards 90-180 degrees; stems slender to thicker, > 0.75 mm in diameter
................................................................................41 Keel petal and the included style either strongly curved upwards 90-180 degrees, or even more extensively coiled (asymmetrically and spirally) in towards the flower center; style or stigma pubescent.
..................................................................................................50 Plants uncinulate pubescent (use 20× magnification, or touch the plant for the 'tacky' feel)
..................................................................................................50 Plants glabrate to villous, the hairs not hooked.
....................................................................................................51 Keel petal and the included style strongly curved upwards 90-180 degrees
......................................................................................................52 Corolla keel symmetrical; [mainly outer Coastal Plain]
......................................................................................................52 Corolla keel usually somewhat twisted, asymmetrical; [widespread in our region]
....................................................................................................51 Keel petal and the included style even more extensively coiled (asymmetrically and spirally) in towards the flower center.
........................................................................................................53 Corolla 2.5-4 cm long, the wings about as long as the other petals; leaflets not lobed
........................................................................................................53 Corolla 1.5-2 cm long, the wing petals longer than the other petals; leaflets lobed

Key to Fabaceae, Key A: woody legumes with all leaves 1-, 2-, or 3-foliolate, or reduced to flattened phyllodia or phyllodial spines

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1 Stamens numerous; inflorescences of many flowers arranged in a closely packed sphere or cylinder; leaves replaced by phyllodes, these leathery in texture and often crescent-shaped; [Mimosoid clade]
1 Stamens 10 (or fewer); inflorescences various, the flowers larger and more diffuse; leaves 1-, 2-, or 3-foliolate, or reduced to phyllodial apines; [subfamily Faboideae or Cercidioideae]
..2 Leaves 1- or 2-foliolate and > 2 cm wide; trees, shrubs, or lianas.
....3 Seeds 1-2 (-4) per fruit; corolla pale yellow, pale pink, or white; longest petals 7-10 mm long; [subfamily Faboideae]
....3 Seeds > 5 per fruit; corolla purplish-pink, bright pink, or white; longest petals 10-100 mm long [subfamily Cercidioideae]
......4 Leaves with a rounded to apiculate apex; flowers strongly bilaterally symmetrical, “pseudopapilionoid”; petals 0.8-1.5 cm long; legumes 4-10 cm long; [natives and aliens, and widely cultivated]
......4 Leaves either unifoliolate with a deeply notched apex or 2-foliolate; flowers slightly bilaterally symmetrical; petals 1.5-8 (-10) cm long; legumes 7-30 cm long; [aliens, of FL peninsula].
........5 Shrub or tree; petals 3-8 (-10) cm long
........5 Liana (climbing by twining and by tendrils); petals 1.5-2.0 cm long
..2 Leaves 3-foliolate, or reduced to phyllodial spines, or 1-foliolate (but then < 2 cm wide); shrubs or woody vines (rarely trees in Erythrina); [subfamily Faboideae].
..........6 Woody vine (Pueraria, a robust herbaceous vine, is also keyed here as a failsafe).
............7 Terminal leaflet 1.5-2.5× as long as wide; legume 4-6 cm wide; seeds 2-3 cm wide; corolla yellow
............7 Terminal leaflet 0.8-1.3× as long as wide; legume 0.8-1.3 cm wide; seeds < 1 cm wide; corolla purplish or red.
..............8 Calyx 4.5-6 mm long; leaflets unlobed; [tribe Phaseoleae]
..............8 Calyx 10-12 mm long; leaflets generally lobed; [tribe Phaseoleae]
..........6 Shrub or tree.
................9 Shrub with angled or flanged green twigs; leaves palmately trifoliolate, unifoliolate, or reduced to spine-tipped phyllodes; [introduced]; [tribe Genisteae].
..................10 Flowers red-purple; calyx 2-3 mm long; [tribe Galegeae]
..................10 Flowers bright yellow; calyx 3-15 mm long; [tribe Genisteae]
....................11 Leaves all reduced to phyllodial spines; flowers axillary; calyx 10-15 mm long
....................11 Leaves with normal lamina, either 1-foliolate or 3-foliolate; flowers in terminal racemes; calyx 3-6 mm long.
......................12 Leaves 3-foliolate lower on the stem, often 1-foliolate above; corolla 15-22 mm long
......................12 Leaves 1-foliolate throughout; corolla either 10-14 mm or 20-25 mm long
........................13 Corolla 10-14 mm long; fruits 1.5-3 cm long
........................13 Corolla 20-25 mm long; fruits 5-10 cm long
................9 Shrub or tree with twigs various, but not conspicuously green or flanged; leaves pinnately trifoliolate or unifoliolate.
..........................14 Leaflet margins toothed; [rare waif]; [tribe Trifolieae]
..........................14 Leaflet margins entire; [collectively common and widespread].
............................15 Leaves unifoliolate; [tribe Genisteae]
............................15 Leaves trifoliolate.
..............................16 Corolla 30-50 mm long, scarlet; legume with several seeds; leaflets lobed or not; [tribe Phaseoleae]
..............................16 Corolla 8-15 mm long, purplish, pink, or white; legume 1-seeded; leaflets not lobed.
................................17 Foliage glandular-punctate; [tribe Psoraleae]
................................17 Foliage eglandular; [tribe Desmodieae]