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Key to TrifoliumView taxon page for Trifolium
(For a list of species in Trifolium, use the above link.) Jepson Manual glossary definitions can be seen by moving your cursor over words underlined with dots. Key to Groups
1. Involucre bracts generally fused, generally > 1 mm, generally forming cup or bowl about base of inflorescence; inflorescence not sessile  Without a petiole, peduncle, pedicel, or other kind of stalk. in leaf  Organ arising from a stem, generally composed of a stalk (petiole) and a flat, expanded, green, photosynthetic area (blade); distinguished from a leaflet by the presence in its axil of a bud, branch, thorn, or flower; sometimes with lateral, basal appendages (stipules); either simple (toothed, lobed, or dissected but not divided into leaflets) or compound (divided into leaflets). axil  Distal, adaxial angle between an appendage or branch and a main axis (e.g., between leaf and stem, or between lateral vein and midrib on a leaf). or above 1–2 leaves ..... Group 1 1' Involucre bracts 0 or occasionally < 1 mm or forming a vestigial ring; inflorescence occasionally ± sessile in leaf axil or above 1–2 ± reduced leaves (stipules of which occasionally involucre-like) ..... Group 2
1. Calyx or banner soon inflated in fruit; involucre  Group of bracts more or less held together as a unit, subtending a flower, fruit (acorn cup), or inflorescence. bracts generally ± free 2. Calyx hairy, inflated in fruit; inflorescence in fruit ± 2 cm wide, spheric, fuzzy; banner not inflating in fruit; perennial  Completing life cycle (germination through death) in more than two years or growing seasons, generally non-woody (at least above ground) to woody; includes perennial herbs as well as subshrubs to trees; the abbreviation 'per' only refers to perennial herb, not to the word 'perennial' alone. herb, stoloned ..... T. fragiferum (2) 2' Calyx glabrous, not inflated in fruit; inflorescence not as above; banner inflating in fruit; annual, not stoloned 4. Calyx tube 1.5–2.5 mm, abaxial lobe  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. tip undivided or 2–3-branched; seed coat net-like ..... T. fucatum 5. Involucre bracts < 1 mm, fused at base; inflorescence generally 1–1.5 cm wide; corolla 6.5–9.5 mm; ScV, nw SnJV, CW ..... T. hydrophilum 5' Involucre bracts 2–2.5 mm, ± free to ± 1/2 fused; inflorescence 0.5–1 cm wide; corolla 4.5–7.5 mm; NCoR, CaRF, SNF, Teh, GV, CW, SCo, ChI, PR ..... T. depauperatum 6. Fruit 3–4 mm, oblong  Longer than wide, with nearly parallel sides; wider than linear. , stalk-like base 0 or short; involucre bracts ± free or ± 1/2 fused, margins widely scarious, toothed near tip; corolla 5–6 mm; GV, SnFrB, SCoR ..... var. amplectens 6' Fruit 2–3 mm, ovate  Egg-shaped (i.e., widest below the middle) in two dimensions (i.e., in one plane), as a leaf. or obovate, stalk-like base 0.5–1 mm; involucre bracts ± free, margins ± membranous; corolla 4.5–7.5 mm; NCoR, CaRF, SNF, Teh, GV, CW, SCo, ChI, PR ..... var. truncatum 1' Calyx, corolla not inflated in fruit (except lower part of banner in Trifolium barbigerum); involucre bracts generally fused into a cup-, bowl-, or wheel-shaped, toothed or cut ring (except generally ± free in Trifolium monanthum) 7. Involucre cup- or bowl-shaped, when pressed generally partly hiding flowers (except in Trifolium grayi) 8. Calyx 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. < 1/2 tube, not bristle-tipped ..... T. microdon 8' Calyx lobes > 1/2 tube, bristle-tipped 9. Calyx lobes, involucre lobes ± entire  Having margins that are continuous and smooth (i.e., without teeth, lobes, etc.). ; plant hairs generally finely wavy ..... T. microcephalum 9' Calyx lobes, involucre lobes, or both toothed, cut, or branched; plant hairs 0 or finely wavy or not 10. Bristle-tips of lower 3 calyx lobes generally forked  Pertaining to a hair or other structure that branches into two parts. ; involucre margin wavy, finely toothed ..... T. cyathiferum 10' Bristle-tips of lower 3 calyx lobes not divided; involucre margin wavy or not, generally coarsely toothed or cut 1/2 to involucre base 11. Calyx lobes finely toothed, bristle at tip 1–1.5 mm, glabrous; involucre generally glabrous; banner not inflated ..... T. buckwestiorum 11' Calyx lobes entire, bristle at tip 3–4 mm, plumose  Plume-like, usually with the parts arrayed in three dimensions around an axis, or in tufts held together at the base; usually pertaining to small, finely divided structures, such as certain stigmas and pappus elements. (or lower lobes divided to near base into 2–3 bristles, each 3–4 mm, generally plumose); involucre generally puberulent  Minutely hairy. ; banner inflated below, persistent as twisted beak above 12. Corolla gold- to sulphur-yellow; leaves, stems glabrous; seeds > 3 mm; ScV (North Table Mtn Plateau, Butte Co.) ..... T. jokerstii 12' Corolla purple, pink-purple, white, or 2-colored; leaves, stems generally hairy; seeds < 3 mm; NW, SN, GV, CW 13. Corolla 5–10 mm, <= (rarely ± >) calyx; stalk-like fruit base < 1 mm; inflorescence generally bristly from calyx lobes ..... T. barbigerum 13' Corolla 8–16 mm, > calyx; stalk-like fruit base 1–3 mm; inflorescence not bristly ..... T. grayi 7' Involucre wheel-shaped or bracts ± free, when pressed hiding only bases of flowers 14. Involucre vestigial or bracts 2–5, inconspicuous, generally ± free, 1–3 mm; inflorescence 1–6-flowered ..... T. monanthum 15. Rhizomes thin, white; plant mat-forming, not from central crown or thickened taproot; plant glabrous to ± hairy 16. Flowers 1–5, peduncle  Stalk of an individual flower borne singly, not in an inflorescence, or of an entire inflorescence, or the corresponding structure in fruit; the stalk subtending an involucre (e.g., in Asteraceae, Polygonaceae). bent upward at tip; leaflet  A leaf-like unit of a compound leaf; distinguished from a leaf by the absence in its axil of a bud, branch, thorn, or flower; lacking lateral, basal appendages (stipules); either simple (leaf 1-compound, with primary leaflets) or compound (leaf 2-compound, with primary and secondary leaflets; 3-compound, with primary, secondary, and tertiary leaflets, etc). tips generally acute  Having a short-tapered, sharp tip, the sides convex or straight and converging at less than a right angle. ; SnGb, SnBr, SnJt ..... subsp. grantianum 16' Flowers 1–4, peduncle straight; leaflet tips generally rounded or truncate  Abruptly (not gradually) narrower or smaller at base or tip, as if cut straight across or nearly so. ; CaR, SN, SNE ..... subsp. monanthum 15' Rhizomes 0; plant not mat-forming, from central crown or thickened taproot; plant densely hairy 14' Involucre generally conspicuous, bracts indefinite in number, generally > 5 mm, fused, if inconspicuous (e.g., 2–3 mm in Trifolium oliganthum) fused at least at base; inflorescence generally 8–many-flowered 18. Perennial herb; involucre generally 2–3 cm wide; seeds 2–4 19. Thickened fusiform  Elongate, widest at the middle, tapered to both ends. root present; rhizomes 0; KR ..... T. siskiyouense 18' Annual; involucre < 2 cm wide; seeds generally 1–2 20. Calyx lobes ± <= tube, often toothed or shouldered below tapered  Gradually (not abruptly) narrower or smaller at base or tip. tip; calyx tube splitting between upper lobes 21. Flower 5–8 mm; involucre 2–3 mm, generally cut > 1/2 to base; inflorescence 6–10 mm wide, 5–15-flowered ..... T. oliganthum 21' Flower 9–18 mm; involucre > 3 mm, cut < 1/2 to base; inflorescence generally 12–30 mm wide, often > 15-flowered 22. Calyx glandular-hairy or bumpy (occasionally in age glabrous), lobes generally entire; leaflets sharply serrate  Having margins with sharp, fine to coarse teeth generally pointing tipward, not outward; margins with such teeth on such primary teeth are doubly serrate. , longer teeth ± 1 mm ..... T. obtusiflorum 20' Calyx lobes generally > tube, generally entire (occasionally ± forked in Trifolium trichocalyx), not shouldered below tapered tip; calyx tube not splitting between upper lobes 23' Calyx generally ± glabrous; involucre generally well developed, cut to middle 24' Calyx bell-shaped, lobes entire or toothed
1. Leaflets 3–9 (at least some leaves with > 3 leaflets) 2' Leaflets 3–7; inflorescence 1–2.5 cm wide 3. Plant silvery or gray, soft-hairy or tomentose  Covered with densely interwoven, generally matted hairs. ; calyx lobe 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. hairs ± 1 mm ..... T. andersonii 4. Longer petiole  Leaf stalk, connecting leaf blade to stem; sometimes more or less indistinct. hairs 1.5–2 mm; peduncles Stalk of an individual flower borne singly, not in an inflorescence, or of an entire inflorescence, or the corresponding structure in fruit; the stalk subtending an involucre (e.g., in Asteraceae, Polygonaceae). generally << petioles Leaf stalk, connecting leaf blade to stem; sometimes more or less indistinct. , inflorescence not or ± exceeding leaves ..... subsp. andersonii 4' Longer petiole hairs 0.4–1.2 mm; peduncles generally > petioles; inflorescence much exceeding leaves ..... subsp. beatleyae 3' Plant green, strigose  With stiff, straight, sharp, appressed hairs. , puberulent Minutely hairy. , or hairy; calyx lobe hairs < 1 mm 5. Leaflet generally elliptic  In the shape of a flattened circle or ellipse; wider than linear , serrate Having margins with sharp, fine to coarse teeth generally pointing tipward, not outward; margins with such teeth on such primary teeth are doubly serrate. , teeth 0.1–0.3 mm; inflorescence generally included  Not protruding out of surrounding structure(s) (e.g., stamens included in corolla). , 1–1.5 cm wide ..... T. gymnocarpon 5' Leaflet obovate, coarsely serrate, larger teeth 0.4–0.5 mm; inflorescence generally exserted  Protruding out of surrounding structure(s) (e.g., stamens exserted from corolla). , 1.5–2.5 cm wide ..... T. lemmonii 6. Flowers of inflorescence, except for outer 2–8, sterile, with calyx stalk-like, without petals, forming bur, delivered to ground by growing peduncle Stalk of an individual flower borne singly, not in an inflorescence, or of an entire inflorescence, or the corresponding structure in fruit; the stalk subtending an involucre (e.g., in Asteraceae, Polygonaceae). ; plant prostrate  Lying flat on the ground. or creeping ..... T. subterraneum 6' Flowers of inflorescence fertile, with calyx not stalk-like, with petals, not forming bur, not delivered to ground by peduncle; plant prostrate or creeping or not 7. Calyx inflated in fruit; inflorescence in fruit spheric or star-shaped, red, brown, green, or white, ± woolly, 0.8–2.5 cm 8. Perennial herb, creeping and rooting or cespitose  Having a densely clumped, tufted, matted, or cushion-like growth form. ; bracts of lower flowers forming involucre Group of bracts more or less held together as a unit, subtending a flower, fruit (acorn cup), or inflorescence. , ± 2 mm, green; corolla not becoming reflexed  Abruptly bent or curved downward or backward. ..... T. fragiferum (2) 8' Annual, decumbent  lying mostly flat on the ground but with tips curving up. to ± erect  Upright; vertically oriented. , not rooting; bracts of lower flowers generally not forming involucre, < 1 mm, white; corolla becoming reflexed 7' Calyx rarely inflated in fruit (if inflated then << 2 cm wide); inflorescence in fruit not as at 7. 10. Leaf pinnately compound; corolla bright yellow 11. Corolla striate; inflorescence 0.8–1.3 cm wide, generally > 20-flowered; petioles of mid-leaves > leaflets ..... T. campestre 11' Corolla weak-striate; inflorescence 0.4–0.8 cm wide, 5–10(20)-flowered; petioles of mid-leaves generally << leaflets ..... T. dubium 10' Leaf palmately compound; corolla not bright yellow (except Trifolium aureum) 12. Leaflets 4–10 cm, stipules 1–2.5 cm, green; calyx glabrous; corolla green-white to pink ..... T. howellii 12' Leaflets or stipules (or both) << above, stipules generally not green; calyx hairy or glabrous; corolla green-white to pink or not 13. Flowers generally 1–5 per inflorescence, bracts generally inconspicuous; corolla white to lavender-striate; plant generally small (see Group 1, couplet 13 for subspecies) ..... T. monanthum (2) 13' Flowers generally > 5 per inflorescence unless plant stressed; corolla white to lavender-striate or not; plant small or not 14. Pedicels 1–6 mm, flowers generally becoming reflexed 15. Corolla bright yellow, 5–7 mm; calyx 1.5–2 mm; stalk-like fruit base 2–3 mm ..... T. aureum 15' Corolla not bright yellow, generally > 6 mm; calyx generally > 2 mm; stalk-like fruit base 0 or < 2 mm 16. Leaflet lanceolate  Narrowly elongate, widest in the basal half, often tapered to an acute tip. ; leaves mostly basal  At or near the base of a plant or plant part. Especially said of leaves clustered near the ground or of a placenta confined to the base of an ovary. , occasionally 2–3 cauline; plants of s SNH, SNE ..... T. dedeckerae 16' Leaflet wider than lanceolate, if lanceolate then leaves not mostly basal or plants not of s SNH, SNE 17. Stem creeping, rooting, turf-forming; petioles from ground level, ± equal; corolla white ..... T. repens 17' Plant not creeping, not rooting, not turf-forming; petioles not or some from ground level, lower > upper; corolla white or not 18. Calyx tube puberulent or hairy, occasionally ± so 19. Corolla 5–8 mm; pedicel  Stalk of an individual flower in an inflorescence, or the corresponding structure in fruit. 2–5 mm ..... T. breweri 20' Longer petals acute Having a short-tapered, sharp tip, the sides convex or straight and converging at less than a right angle. to acuminate  Having a long-tapered, sharp tip, the sides concave. but not beaked; 1200–2700 m 21. Stems generally well developed, not cespitose; petals generally white, short-tapered, acute, or obtuse  Having a short-tapered, blunt tip or base, the sides convex or straight and converging at more than a right angle. ; 1200–1800 m; KR, NCoR ..... subsp. oreganum 21' Stems often poorly developed, generally cespitose; petals lavender to purple, longer ones acute to acuminate; 1400–2700 m; KR, CaR ..... subsp. shastense 22. Calyx 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. ciliate  Having generally straight, conspicuous hairs along margins or edges. with short, flat bristles (or, through breakage, bristle bases); bracts inconspicuous, often in a ring at base of inflorescence ..... T. ciliolatum 22' Calyx lobes not ciliate; bracts subtending individual flowers or 0 23' Leaves cauline; corolla 5–11 mm 24. Inflorescence 1.5–3 cm wide; bracts conspicuous but soon falling; calyx lobes sharply tapered but not bristle-tipped ..... T. hybridum 24' Inflorescence 0.5–1.5 cm wide; bracts 0; calyx lobes bristle-tipped 25. Calyx lobes ± 0.5 mm wide at base, glabrous, tube 1.5–2.5 mm 25' Calyx lobes ± 0.2 mm wide at base, with generally few hairs, tube 0.8–1.4 mm ..... T. bifidum 14' Pedicels < 2 mm, flowers becoming reflexed or not 27. Inflorescence sessile Without a petiole, peduncle, pedicel, or other kind of stalk. at end of stem or in leaf Organ arising from a stem, generally composed of a stalk (petiole) and a flat, expanded, green, photosynthetic area (blade); distinguished from a leaflet by the presence in its axil of a bud, branch, thorn, or flower; sometimes with lateral, basal appendages (stipules); either simple (toothed, lobed, or dissected but not divided into leaflets) or compound (divided into leaflets). axils, or in leaf axils on short peduncles 6–10 mm, << leaves; corolla 2.5–6 mm 28. Inflorescence axillary  Pertaining to or within an axil, especially a leaf axil. or at end of stem, peduncles 0 28' Inflorescence axillary, peduncles short or short below, 0 above 30' Corolla < calyx lobes; banner tip occasionally ± toothed but not notched; peduncles short below, 0 above ..... T. retusum 27' Inflorescence peduncled (or immediately above 1–2 reduced leaves), peduncle generally > 10 mm, generally > leaves; corolla generally > 5 mm 31' Banner not inflated in fruit; involucre 0; corolla 6–9 mm or not 32. Flowers generally reflexed soon after opening; inflorescence often turned to side or downward 33. Calyx hairy, lobes twisted or bent, plumose Plume-like, usually with the parts arrayed in three dimensions around an axis, or in tufts held together at the base; usually pertaining to small, finely divided structures, such as certain stigmas and pappus elements. ..... T. eriocephalum subsp. eriocephalum 33' Calyx glabrous, lobes not twisted or bent, not plumose 34. Inflorescence 1–2 cm wide; calyx 3.5–4.5 mm, generally dark or purple-black; corolla 10–12 mm ..... T. bolanderi 34' Inflorescence 1.5–3 cm wide; calyx 3–7 mm, not dark or purple-black; corolla 10–17 mm 35' Calyx 3–4 mm; inflorescence generally turned to side or downward, axis exserted, generally forked Pertaining to a hair or other structure that branches into two parts. ..... T. productum 32' Flowers generally not reflexed after opening; inflorescence generally ± erect 36. Inflorescence ± sessile above a pair of reduced leaves, stipules, or both (in Trifolium macraei, occasionally 1 of a pair of inflorescences short-peduncled) 37. Inflorescence generally paired, ± sessile or occasionally 1 short-peduncled above (1)2 leaves ..... T. macraei 37' Inflorescence single above subtending leaves 38. Corolla 2-colored (purple with white tips); locally uncommon, s NCoR, n CCo, SnFrB ..... T. amoenum (2) 38' Corolla not 2-colored (red-purple or pink); sporadic or locally common, CA-FP, GB 39. Calyx lobes densely to sparsely plumose, lower one ± 1–1.5 × others; corolla pink 40. Inflorescence spheric, ± 1.5–2 cm; calyx lobes >> tube, densely plumose, 4–6 mm ..... T. hirtum 40' Inflorescence ± short-cylindric, 0.5–1.5 cm; calyx lobes <= tube except lower one, sparsely plumose, 1–2.5 mm ..... T. striatum 39' Calyx lobes sparsely plumose, straight, lower one ± 2 × others, or calyx lobes glabrous, curved, ± equal; corolla red-purple or pink 41. Leaflets elliptic to obovate, ± entire Having margins that are continuous and smooth (i.e., without teeth, lobes, etc.). ; calyx hairy, veins 10, lobes straight; corolla generally red-purple ..... T. pratense 41' Leaflets generally lanceolate to elliptic, teeth bristle-like; calyx glabrous, veins 24, lobes straight to curved; corolla pink to purple ..... T. vesiculosum 36' Inflorescence peduncled 42. Corolla <= calyx; calyx lobes > tube, plumose 43. Leaflets oblanceolate to obovate, length 1.2–3 × width; corolla 2-colored (purple with white tips) 43' Leaflets linear  Elongate, with nearly parallel sides; narrower than elliptic or oblong. to narrow-lanceolate, -oblong, or -oblanceolate, length 3–8 × width; corolla 1-colored (pale pink to white) 42' Corolla > calyx; calyx lobes > tube or not, plumose or not 46. Perennial herb; calyx lobes glabrous or hairs few, curved or wavy 47. Inflorescence < 1 cm wide, flowers generally 1–5, erect (see Group 1, couplet 13, for subspecies) ..... T. monanthum (2) 48. Calyx lobes 3–5 × tube; leaflet A leaf-like unit of a compound leaf; distinguished from a leaf by the absence in its axil of a bud, branch, thorn, or flower; lacking lateral, basal appendages (stipules); either simple (leaf 1-compound, with primary leaflets) or compound (leaf 2-compound, with primary and secondary leaflets; 3-compound, with primary, secondary, and tertiary leaflets, etc). length generally 6–10 × width; KR, NCoR, CaR ..... subsp. elmeri 48' Calyx lobes 1–3 × tube; leaflet length 2–6 × width in CA-FP, to 10 × in GB; KR, NCoR, CaR, SN, SnBr, SnJt, GB 49. Roots thickened, fusiform Elongate, widest at the middle, tapered to both ends. ; rhizomes ± 0; calyx lobes densely long-hairy ..... subsp. atrorubens 46' Annual; calyx lobes ± plumose, hairs generally straight 50. Corolla 2-colored (purple with white tips) 50' Corolla 1-colored (purple, crimson, pink, white, or cream) 52. Corolla cream; inflorescence ovate Egg-shaped (i.e., widest below the middle) in two dimensions (i.e., in one plane), as a leaf. to spheric, 1–2.5 cm; leaflets elliptic to oblanceolate; stipules long-tapered ..... [T. alexandrinum] 52' Corolla crimson or white; inflorescence ± cylindric  Elongate, with parallel sides and, at any point, round in transverse section. or ± conic, 2–6 cm; leaflets obovate to obcordate; stipules widely rounded ..... T. incarnatum
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