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See list of 19 species in this genus

Trifolium macraei Hook. & Arn. was first reported from New England by Knowlton and Deane (1918), and has been reported in other floras since (e.g., Kartesz 1999). The specimen on which this record was based was determined to be T. incarnatum by Sorrie and Somers (1999). Trifolium carolinianum Michx. was reported from VT by Atwood et al. (1973), but specimens are unknown. Reference: Coombe (1968).

  • 1a. Flowers yellow, turning brown after anthesis
    • 2a. Central leaflet sessile or on a petiolule of ± similar length as the lateral leaflets; corollas 5–7 mm long; inflorescence 10–17 (–20) mm tall; stipules ± as long as the petioles; style 1–2 mm long
    • 2b. Central leaflet borne on a petiolule conspicuously longer than those of the lateral leaflets [Fig. 653]; corollas 3.5–5 (–6) mm long; inflorescence 5–15 mm tall; stipules shorter than the petioles; style less than 1 mm long
      • 3a. Petiolule of the central leaflet up to 1 mm long; inflorescence with usually 5–15 flowers; corollas 3–3.5(–4) mm long; banner petal inconspicuously veined
      • 3b. Petiolule of the central leaflet 1–3 mm long; inflorescence with usually 20–30 flowers; corollas (3.5–) 4–5 (–6) mm long; banner petal with 10 conspicuous veins
  • 1b. Flowers white to pink to purple
    • 4a. Flowers pedicellate, the pedicels usually longer than 2 mm; petals white or white and pink
      • 5a. Stems creeping along the ground, rooting at the nodes; petals usually concolored; stipules connate to the petiole in the basal portion, then with fused margins for a distance, forming a tube that surrounds the stem
      • 5b. Stems ascending, not rooting at the nodes; petals bicolored; stipules connate to the petiole in the basal portion, then distinct, the tips completely separate and not forming a tube
    • 4b. Flowers sessile or subsessile, the pedicels (when present) up to 0.5 mm long; petals white to pink to purple
      • 6a. Basal connate portion of calyx more densely pubescent on the upper side, becoming obliquely inflated in fruit, the upper side gibbous; flowers each subtended 
by a bracteole, resupinate (i.e., twisted within the calyx such that the banner petal 
is in a lateral or lower position; not resupinate in T. fragiferum) [Fig. 655]
      • 6b. Basal connate portion of calyx uniformly glabrate or pubescent, not becoming obliquely inflated in fruit; flowers lacking bracteoles (with bracteoles in T. glomeratum), not resupinate (i.e., the banner petal uppermost)
        • 9a. Outer 2–4 (–6) flowers of each inflorescence bearing petals and fertile, the remaining flowers on the interior apetalous and sterile; inner flowers eventually elongating and producing a mass of woody, plumose stalks that surround the fruiting calyces and form a compact bur that is pushed against the soil surface or below it by downward growth of the peduncle; stems prostrate, stolon-like
        • 9b. All the flowers of each inflorescence bearing petals and fertile; fruiting inflorescence not resembling a compact bur and not pushed against soil surface or below it; stems ascending to erect (sometimes procumbent in T. echinatum and 
 T. glomeratum)

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