Arachis
Arachis hypogaea
peanut
earthroot, peanut
spreading, erect, prostrate, or creeping, sometimes subterranean, glabrous or pubescent.
spreading, erect, or prostrate, sometimes rooting at nodes, to 13 dm, glabrous or villous.
alternate, usually even-pinnate;
stipules present, adnate to petiole base;
petiolate;
leaflets usually 4, rarely 3, stipels absent, blade margins entire, surfaces glabrous or pubescent.
stipules lanceolate to subfalcate, 20–30(–50) mm;
leaflet blade elliptic to ovate or obovate, 18–60 × 15–30 mm, apex often obtuse to subacute, sometimes emarginate, surfaces glabrous, or puberulent abaxially, margins villous, sometimes bristly.
1–7-flowered, axillary, spikes, sometimes subpaniculate;
bracts present, similar to stipules;
bracteoles paired at base of elongated hypanthium.
papilionaceous;
calyx, corolla, and stamens borne at summit of an elongated, tubular hypanthium, calyx lobes 5, bilabiate, linear, 4 adaxial lobes connate to form broad lip, sometimes 2 adaxialmost lobes fused to summit and adaxial lip appearing 3-toothed;
corolla yellow to orange [brick-red or white];
stamens 10, monadelphous, with 8 functional anthers and 2 sterile filaments [9 or 10 functional and 0 or 1 sterile];
anthers alternately dorsifixed, oblong, and basifixed, globose, sometimes 1 or 2 stamens reduced to sterile filaments or absent;
ovary sessile at anthesis, base later greatly elongated on peg;
style filiform;
stigma terminal.
hypanthium elongated, (1–)2–4 cm;
calyx 10–12 mm, glabrous;
corolla bright yellow to orange, often with reddish lines toward base of banner, 10–20 mm.
geocarpic, loments, sessile, torulose, not articulate, oblong or ovoid, ± indehiscent, glabrous.
1–6, ovoid or oblong;
hilum subapical.
oblong;
testa reddish brown.
oblong, 20–60 × 10–20 mm, sometimes constricted between seeds;
pericarp reticulate.
= 10.
= 40.
Arachis
Arachis hypogaea
Species ca. 70 (2 in the flora).
Arachis is most closely related to Chapmannia and Stylosanthes, based on morphological (V. E. Rudd 1981) and molecular evidence (M. Lavin et al. 2001, 2001b). It has been divided into nine sections, with many species displaying extensive morphological variation (A. Krapovickas and W. C. Gregory 2007). Two species are cultivated in the flora area for use as food or forage. Additional species are grown in tropical climates; they may be introduced into southern Florida in the future. Some cultivated strains are difficult to identify to species and are identified only to section.
Geocarpic fruits are common to all species of Arachis. The flowers are chasmogamous and aerial, with a meristem at the base of the sessile ovary. After fertilization, the meristem elongates greatly to form a post-floral axis or the so-called peg that grows gravitropically until the developing fruit is below ground level (B. W. Smith 1950; A. Krapovickas and W. C. Gregory 2007).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Arachis hypogaea is a major cultivated crop in tropical to warm-temperate areas worldwide (R. Prescott-Allen and C. Prescott-Allen 1990); the seeds are used most notably as food or for edible oil (J. A. Duke 1981). Archaeological evidence indicates that peanuts were in cultivation by at least 1200–1500 BCE and spread as far north as Mexico prior to European contact (R. O. Hammons 1973). Peanuts occur sporadically outside of cultivation, probably spread by birds and squirrels; they are rarely self-perpetuating. The infraspecific variation of A. hypogaea in its native range is extensive; it has been divided into two subspecies and six varieties (A. Krapovickas and W. C. Gregory 2007). The variation in its native range may be useful in improving the cultivated strains (J. Smartt 1990).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Herbs annual; calyces 10–12 mm; corollas 10–20 mm; hypanthia elongated to (1–)2–4 cm; loments 20–60 × 10–20 mm. | A. hypogaea |
1. Herbs perennial; calyces 6–10 mm; corollas 15–24 mm; hypanthia elongated to 2.5–10 cm; loments 10 × 5–6 mm. | A. glabrata |
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