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Trifolium
See list of 19 species in this genusTrifolium 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).
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1a. Flowers yellow, turning brown after anthesis
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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
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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
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3a. Petiolule of the central leaflet up to 1 mm long; inflorescence with usually 5–15 flowers; corollas 3.5–4 mm long; banner petal inconspicuously veined
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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
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1b. Flowers white to pink to purple
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4a. Flowers pedicellate, the pedicels usually longer than 2 mm; petals white or white and pink
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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
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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
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4b. Flowers sessile or subsessile, the pedicels (when present) up to 0.5 mm long; petals white to pink to purple
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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]
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7a. Flowers not resupinate; peduncles (20–) 40–80 (–200) mm long; plants perennial, usually stoloniferous
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7b. Flowers resupinate; peduncles up to 50 mm long; plants annual, not stoloniferous
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8a. Inflorescence mostly 10–20 mm in diameter, lobulate in fruit, borne on elongate peduncles 20–50 mm long; stems 10–40 (–60) cm tall
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8b. Inflorescence mostly 5–10 mm in diameter, hemispheroid to spherical in fruit, subsessile or borne on a peduncle shorter than 20 mm; stems 5–15 cm tall
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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)
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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
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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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10a. Corollas 3–4 mm long, definitely shorter than the calyx; leaflets narrow-oblanceolate to oblanceolate or narrow-oblong, 3–5.5 times as long as wide [Fig. 652]
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10b. Corollas 4–16 mm long, ± as long as or longer than the calyx; leaflets of lower leaves obovate or obcordate to elliptic, 0.8–3 times as long as wide (sometimes oblanceolate and up to 4 times as long as wide in T. dichotomum)
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11a. Corollas 4–6 mm long, ± as long as or shortly exceeding the calyx; inflorescences sessile or subsessile
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12a. Flowers subtended by bracteoles; basal connate portion of the calyx glabrous
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12b. Flowers without bracteoles; basal, connate portion of the calx pubescent
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11b. Corollas (6–) 8–25 mm long, definitely longer than the calyx; inflorescences sessile or pedunculate
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13a. Inflorescence sessile or on peduncles to 20 (–30) mm long, subtended either by a pair of opposite leaves or their expanded stipules or by an involucre (i.e., a ring of fused bracts); plants perennial (annual in T. dalmaticum)
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14a. Inflorescence subtended by an involucre; corolla 8–10 mm long, pink; plants annual
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14b. Inflorescence subtended by a pair of opposite leaves or their expanded stipules [Fig. 654]; corolla 12–20 mm long, red-purple to purple-red (very rarely cream-white in T. pratense); plants perennial
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15a. Distinct portion of the stipule broad-triangular, shorter than the connate portion; leaflets ovate or obovate to elliptic, 1.2–2.5 times as long as wide, frequently with light mottles on the adaxial surface
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15b. Distinct portion of the stipule lanceolate, longer than the connate portion; leaflets elliptic to oblong, 2–3 times as long as wide, usually without light mottles
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13b. Inflorescence borne on peduncles 10–70 mm long, not subtended by a pair of opposite leaves or an involucre (i.e., all the leaves alternate; except T. echinatum); plants annual
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16a. Corollas 16–25 mm long; leaflets linear to elliptic-oblong, 20–50 ×2.5–5 mm
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16b. Corollas 5–12 mm long; leaflets oblanceolate or elliptic to obovate or obcordate, 8–30 ×3–12 mm
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17a. Peduncles subtended by a pair of opposite leaves; calyx lobes stiff and spinose, especially in fruit
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17b. Peduncles subtended by a single leaf; calyx lobes pliable, not spinose
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18a. Corollas red (rarely white); inflorescence conic to cylindric, (20–) 30–60 mm tall, at least the taller ones greater than 3 times as tall as wide; leaflets obovate to obcordate, 0.8–1.2 times as long as wide
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18b. Corollas purple with white near the apex (or with the reverse coloration); inflorescence ovoid to short-cylindric, up to 30 mm tall, less than 3 times as tall as wide; leaflets oblanceolate or obovate to elliptic, 1.5–4 times as long as wide
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Each photo represents one species in this genus.