Trifolium subterraneum |
Trifolium oliganthum |
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burrowing clover, subclover, subterranean clover, subterranean trefoil |
few-flower clover, few-flowerered clover |
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Habit | Herbs annual, 10–80 cm, glabrous or appressed-pubescent. | Herbs annual, 10–50 cm, glabrous. |
Stems | prostrate to ascending, branched. |
erect, dichotomously branched. |
Leaves | palmate; stipules ovate, 0.5–3 cm, margins entire or slightly toothed, ciliate, apex acute to acuminate; petiole 1–20 cm; petiolules 1 mm; leaflets 3, blades broadly obcordate, 0.8–2.8 × 1–3 cm, base cuneate, veins delicate, widely spaced, margins mostly entire, slightly dentate distally, apex emarginate, surfaces appressed-sericeous. |
palmate; stipules lanceolate, 0.4–1.2 cm, margins lacerate, apex subulate; petiole 0.5–4 cm; petiolules to 0.5 mm; leaflets 3, blades linear, oblong, oblanceolate, or elliptic, 0.5–2.5 × 0.1–0.5 cm, base cuneate, veins fine or moderately thickened, margins entire, spinulose, or dentate, apex rounded or truncate, mucronate, surfaces glabrous. |
Inflorescences | axillary, elongate and reflexed, pushing into substrate after anthesis, fertile flowers 2–7, sterile flowers 0–80, globose or cylindric, 0.5–1.5 × 0.8–1.5 cm; involucres absent. |
axillary or terminal, 3–15-flowered, obconic, 0.3–1.2 × 0.3–0.8 cm; involucres flattened to bowl-shaped, 1–2 mm, when folded, not hiding flowers except proximally, incised 4/5–9/10 their length, lobes lanceolate-subulate. |
Peduncles | 2–6.5 cm. |
2.5–7.5 cm. |
Pedicels | reflexed after anthesis, 0.2–0.4 mm; bracteoles absent. |
erect, 0.5–2 mm; bracteoles absent. |
Flowers | fertile ones 7–15 mm; calyx tubular, 5–6 mm, glabrous or hairy, veins indistinct, tube 3–4 mm, lobes subequal, pubescent or glabrous, spreading, orifice open; corolla white, pink, or pink-striped, 7–10 mm, banner ovate-elliptic, 7–10 × 1.5–2 mm, apex rounded; sterile flowers 4–7 mm; calyx teeth linear; corolla absent. |
11–16 mm; calyx campanulate, slit between adaxial lobes, 4–5 mm, glabrous, veins 10, tube 2.5–5.2 mm, lobes triangular-subulate, 3-fid or shouldered below apex, orifice open; corolla lavender with white tips, keel petals purple, 6–8 mm, banner narrowly ovate-oblong, 6–8 × 2 mm, apex narrowly rounded, erose. |
Legumes | subterranean, obovoid, 3–4 mm. |
sessile, oblong, 2.1–3.2 mm. |
Seeds | 1, purplish black, ellipsoid, 2.6–3 mm, smooth, dull. |
1 or 2 (or 3), reddish brown, mottled, lenticular or reniform, 1.2–1.3 mm, smooth. |
2n | = 16. |
= 16. |
Trifolium subterraneum |
Trifolium oliganthum |
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Phenology | Flowering Mar–May. | Flowering Mar–Jul. |
Habitat | Open, disturbed sandy soils. | Stream banks, grassy, rocky slopes, meadows, fields. |
Elevation | 0–1000 m. (0–3300 ft.) | 0–1100 m. (0–3600 ft.) |
Distribution |
CA; GA; LA; MA; MS; NC; NJ; OR; SC; WA; BC; w Europe; w Asia; n Africa [Introduced in North America; introduced also in s South America, s Africa, Pacific Islands (Hawaii, New Zealand), Australia]
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CA; OR; WA; BC
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Discussion | Trifolium subterraneum was first introduced by the USDA about 1921 as a pasture crop; it is utilized as such in the western and southern United States (W. S. McGuire 1985). Inflorescences of T. subterraneum consist of intermixed sterile and fertile flowers; after fetilization, the inflorescence is pushed underground, where the fruits develop. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Trifolium oliganthum is relatively common throughout much of its range in California; it is found in a few scattered sites northward into Oregon, Washington, and British Columbia. Even though it closely resembles T. variegatum, it is placed near T. bifidum in molecular studies (N. W. Ellison et al. 2006). Trifolium hexanthum Greene ex A. Heller, which pertains here, is not a validly published name. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 11. | FNA vol. 11. |
Parent taxa | ||
Sibling taxa | ||
Synonyms | T. pauciflorum, T. filipes, T. oliganthum var. sonomense, T. triflorum | |
Name authority | Linnaeus: Sp. Pl. 2: 767. (1753) | Steudel: Nomencl. Bot. ed. 2, 2: 707. (1841) |
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