Prosopis L., Mantissa Pl. 68: 10. 1767.

Figs 135, 137

Lagonychium M. Bieb., Fl. Taur.-Caucas. 3: 288. 1819. Type: Lagonychium stephanianum M. Bieb. [= Prosopis farcta (Banks & Sol.) J.F. Macbr.]

Prosopis sect. Adenopis DC., Prodr. [A.P. de Candolle] 2: 446. 1825. Type: Prosopis spicigera L. [= Prosopis cineraria (L.) Druce]

Pleuromenes Raf., Sylva Tellur.: 144. 1838. Type: Pleuromenes heterocarpa (Delile) Raf. [≡ Acacia heterocarpa Delile (= Prosopis farcta (Banks & Sol.) J.F. Macbr.)]

Type.

Prosopis spicigera L. [= Prosopis cineraria (L.) Druce]

Description.

Prickly subshrubs, shrubs, small trees (Fig. 135D) or occasionally lianescent ( P. farcta), 0.3-6.5 (-10) m, deep-rooted and sometimes invading via root suckers, prickles internodal, scattered, straight, somewhat acroscopic, conical with broad bases (Fig. 135E), stipular spines or axillary thorns absent; brachyblasts absent. Stipules inconspicuous and caducous. Leaves bipinnate, an obscure gland between lower pair of pinnae; pinnae 1-6 (7) pairs, opposite/alternate; leaflets 7-15 pairs per pinna, opposite/alternate, mid-vein excentric. Inflorescences spiciform racemes, axillary, solitary or in fascicles (Fig. 135G), peduncle sometimes with an amplexicaul bract, this caducous and leaving an oblique scar. Flowers yellow, yellowish-white, green, or creamish-green; calyx truncate, sepals 5, valvate; petals 5, valvate, nearly free, reflexed; stamens 10, free, anthers with a minute caducous incurved claviform gland arising from the connective; pollen in tricolporate monads, pores without costae, exine irregularly areolate-verrucose, columellae present; ovary sessile or shortly stipitate, stigma porate. Fruits indehiscent, slender, cylindrical to sub-cylindrical in cross-section, torulose, mesocarp spongy, endocarp segments thin, little developed, seed chambers longitudinal or transverse (Fig. 135I). Seeds well separated, compressed, pleurogram present, not closed, testa hard.

Chromosome number.

2 n = 28 (Goldblatt 1981b), polyploidy reported in P. koelziana: 2 n = 28, 52 (Zaeifi et al. 2002).

Included species and geographic distribution.

Three species distributed across arid parts of north Africa (but apparently the genus rare at its western limits in Libya and Tunisia), the Middle East, Pakistan and north-western India (especially Punjab and Rajasthan) and reaching its northern limits in Azerbaijan (Fig. 137).

Ecology.

Abundant in dry and arid parts of north-western India, where P. cineraria is sometimes the most common tree in parts of Punjab and Rajasthan (Fig. 135D) and abundant in arid thorn scrub in parts of the Middle East, where P. farcta (Banks & Sol.) J.F. Macbr. can spread via root suckers, and is sometimes considered weedy, tolerating saline soils. The fruits are eagerly consumed by herbivores, including livestock and this facilitates endozoochorous seed dispersal.

Etymology.

Pasiecznik et al. (2001) suggested the name to be derived from pros - (Greek = towards) and - Opis (wife of Saturn, the Greek goddess of abundance and agriculture), hence 'towards agriculture’ referring to the widespread utility of the genus.

Human uses.

Prosopis cineraria is a highly valued tree, protected and cultivated in silvopastoral and other agroforestry systems as a source of high-quality durable wood, leaves for fodder, fruits for livestock feed and flowers as bee forage (Leakey and Last 1980) (Fig. 135D).

Notes.

Although P. cineraria and P. farcta are well-known, easily distinguished and widely distributed species, the third species of the genus, P. koelziana Burkart, is poorly-known from just a handful of collections from Iran. It has fruits similar to P. farcta and leaves similar to P. cineraria, and was suggested by Burkart (1976) to be of putative hybrid origin between these two species. In north-western India and Pakistan, introduced Neltuma juliflora (Sw.) Raf. is frequently found alongside native P. cineraria and the two are often confused having similar leaves and fruits, but can be distinguished based on armature.

Taxonomic references.

Burkart (1976); Hughes et al. (2022b).