Arachis

Herbs, annual or perennial, sometimes woody basally, unarmed. Stems spreading, erect, prostrate, or creeping, sometimes subterranean, glabrous or pubescent. Leaves 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. Inflorescences 1–7-flowered, axillary, spikes, sometimes subpaniculate; bracts present, similar to stipules; bracteoles paired at base of elongated hypanthium. Flowers 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. Fruits geocarpic, loments, sessile, torulose, not articulate, oblong or ovoid, ± indehiscent, glabrous. Seeds 1–6, ovoid or oblong; hilum subapical. x = 10.

Distribution

Introduced; South America (Argentina, Brazil, Paraguay, Uruguay), introduced also in Mexico, West Indies, Central America, Asia, Africa, Australia.

Discussion

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).

Selected References

None.

Lower Taxa

Arachis glabrata, Arachis hypogaea

Key

1	Herbs annual; calyces 10–12 mm; corollas 10–20 mm; hypanthia elongated to (1–)2–4 cm; loments 20–60 × 10–20 mm.	Arachis hypogaea
1	Herbs perennial; calyces 6–10 mm; corollas 15–24 mm; hypanthia elongated to 2.5–10 cm; loments 10 × 5–6 mm.	Arachis glabrata