Prosopis L., Mantissa Pl. 68: 10. 1767. emend. C.E. Hughes & G.P. Lewis.

Hughes, Colin E., Ringelberg, Jens J., Lewis, Gwilym P. & Catalano, Santiago A., 2022, Disintegration of the genus Prosopis L. (Leguminosae, Caesalpinioideae, mimosoid clade), PhytoKeys 205, pp. 147-189 : 147

Prosopis L., Mantissa Pl. 68: 10. 1767. emend. C.E. Hughes & G.P. Lewis.

Lagonychium M. Bieb., Fl. Taur.-Caucas. 3: 288. 1819.

Prosopis section Adenopis DC., Prodr. 2: 446. 1825.

Pleuromenes Raf., Sylva Tellur.: 144. 1838.

Type.

Prosopis spicigera L., a synonym of P. cineraria (L.) Druce.

Description.

Prickly subshrubs, shrubs, small trees or occasionally lianescent ( P. farcta ), 0.3-6.5 (-10) m high, deep-rooted and sometimes invading via root suckers, prickles internodal, scattered, straight, somewhat acroscopic, conical with broad bases, 3-5 mm long (Figs 2C, M and 3C ), stipular or axillary spines absent. Stipules foliaceous, ovate-acute, caducous. Leaves with 1-6 (-7) pairs of pinnae, the petiole and rachis 0.5-4 cm, sometimes a prickle at the base of the petiole, the pinnular rachises 2-7 cm long, with 7-15 pairs of leaflets, these ovate or lanceolate, straight to sub-falcate or auriculate, mucronate, 2-15 × 2-4.5 mm, glabrous, puberulous or pubescent, mid-vein excentric. Inflorescences spicate, 4-13 cm long, axillary, solitary or in fascicles, peduncle sometimes with an amplexicaul bract, this caducous and leaving an oblique scar; pedicels 0.5-1.5 mm. Flowers small, yellow, yellowish-white, green or cream-green; calyx truncate, 0.8-1.2 mm long; corolla 3.5-4 mm long, the petals linear, nearly free, reflexed, glabrous on both sides; anthers with a minute caducous incurved claviform gland arising from the connective; pollen lacking costae on the pores, tectum irregularly areolate-verrucose. Fruits indehiscent, slender, elongate straight or sub-falcate, dark reddish-brown to blackish, shiny, cylindrical to sub-cylindrical, torulose, 1.5-19 × 0.4-2.5 cm, exocarp thin, brittle, shiny and smooth, orange-red becoming brown, red or black when ripe (Fig. 7C ), mesocarp spongy, endocarp segments thin, little developed, seed chambers longitudinal or transverse. Seeds well separated, longitudinal, ovate to ovoid, compressed, 6-8.5 × 5-6 × 2.5-3 mm.

Geographic distribution.

Reduced now to just three Old World species, these distributed across arid parts of North Africa (but apparently the genus rare at its western limits in Algeria and Tunisia), the Middle East and NW India (especially Punjab and Rajasthan) and reaching its northern limits in Afghanistan and Azerbaijan (Fig. 8 ).

Habitat and uses.

Abundant in dry and arid parts of NW India, where it is sometimes the most common tree in parts of Punjab and Rajasthan and abundant in arid thorn scrub in parts of the Near East (where P. farcta , which can spread via root suckers, is sometimes considered weedy), tolerating saline soils. Highly valued as a source of high quality durable wood, pods for livestock feed and bee forage.

Etymology.

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

Affinities.

Prosopis s.s. is here reduced to three species and is sister to the monospecific genus Indopiptadenia (Fig. 1 ). These two genera share stem/internodal prickles and a W-C Asian distribution that is unique within mimosoids.

Figures

Figure 1. A Phylogeny of the Caesalpinioideae showing the placement of the Prosopis grade (boxed in red) within the subfamily, based on analyses of DNA sequences of 997 nuclear genes (Ringelberg et al. 2022) B the part of the phylogeny that includes all elements of Prosopis s. l. Genera recognised in the new generic system presented here are in bold. Pie charts show the fraction of gene trees supporting that bipartition in blue, the fraction of gene trees supporting the most likely alternative configuration in green, the fraction of gene trees supporting additional conflicting configurations in red and the fraction of uninformative gene trees in grey. Numbers above pie charts are Extended Quadripartition Internode Certainty (Zhou et al. 2020) scores. Branch lengths are expressed in coalescent units and terminal branches were assigned an arbitrary uniform length for visual clarity, see Ringelberg et al. (2022); the root is not drawn to scale C, D the two most likely alternative tree topologies which would allow for a monophyletic Prosopis s. l., either without (C) or with (D) Xerocladia and Indopiptadenia. In C and D numbers above pie charts = number of gene trees supporting the species tree, numbers below pie charts = number of gene trees conflicting with the species tree C lack of gene tree support (just 69 gene trees) for the alternative species tree topology where sections Algarobia + Monilicarpa (≡ Neltuma) are sister to section Strombocarpa (≡ Strombocarpa) vs. 573 genes supporting a sister group relationship between Strombocarpa and Xerocladia (as shown in D) D lack of gene trees (zero gene trees) supporting a monophyletic Prosopis s. l.

Figure 2. Variation in armature of Prosopis, Strombocarpa, Neltuma and Xerocladia A Neltuma denudans (nodal spines on a zig-zag stem) B N. humilis (paired striate spine-tipped branches) C Prosopis cineraria (scattered internodal prickles) D Neltuma sericantha (spine-tipped stems) E Strombocarpa burkartii (stipular spines) F Neltuma argentina (single nodal axillary spine) G N. kuntzei (spinescent shoots) H Strombocarpa ferox (stipular spines) I S. strombulifera (stipular spines) J Neltuma elata (variation in paired nodal spines on one specimen) K N. alba (paired nodal spines) L N. velutina (paired nodal spines) M Prosopis farcta (scattered internodal prickles) N Neltuma ruscifolia (single nodal axillary spine) O Xerocladia viridiramis (recurved, deflexed stipular spines) (5 cm scale bar). All specimens at K A drawn from Seijo 1489 B Tweedie s. n. C Willcox 299 D MERL 8792 E Acosta & Rosas 748 F Guaglianone et al. 1762 G Nee & Coimbra 35556 H Atahuachi et al. MA 1147 I Hunziker 2036 J Legname & Cuezzo 10396 (large and small spines from same specimen) K Hughes & Forrest 2312 L Harding & Balsinhas 140 M Guest et al. 17463 N Wood & Mamani 14063 O Kolberg & Tholkes HK 2493. Drawn by Andrew Brown, July 2021.

Figure 3. Variation in armature across Prosopis s. l. and allies A stipular spines of Strombocarpa strombulifera B internodal prickles on shoots and branches of Indopiptadenia oudhensis which it shares with its sister group, Prosopis s. s. illustrated in C; C internodal prickles of Prosopis farcta D stipular spines of Xerocladia viridiramis which it shares with its sister group, the genus Strombocarpa illustrated in A; E axillary nodal spines of Neltuma juliflora F spinescent straight cylindrical shoots of the subaphyllous Neltuma kuntzei. Photos courtesy of Guillermo Debandi (A) (see https // www. inaturalist. org / taxa / 78750 - Prosopis-strombulifera / browse _ photos), Dr. Omesh Bajpai and Dr. Lal Babu Chaudhary (B), Zeynel Cebeci (C) (see https // commons. wikimedia. org / wiki / FileProsopis _ farcta _ - _ Syrian _ mesquite _ 01), N. Dreber (D) (see http // www. southernafricanplants. com /), Colin Hughes (E, F).

Figure 7. Variation in fruits across Prosopis s. l. and allies A indehiscent pods of Anonychium africanum with thick pulpy mesocarp collected as fodder for livestock B plano-compressed pods of Indopiptadenia oudhensis lacking a thickened mesocarp and dehiscent along both sutures C indehiscent fruits of Prosopis farcta with a thick pulpy mesocarp D tightly coiled indehiscent screwbean fruits of Strombocarpa strombulifera E indehiscent pods of Strombocarpa ferox with a thick pulpy mesocarp F indehiscent fruits of Strombocarpa palmeri G small reniform to flabellate, flattened, indehiscent, 1 (- 2) - seeded, winged fruits of Xerocladia viridiramis which are unique within mimosoid legumes H indehiscent fruits of Neltuma articulata with a thick mesocarp and a hard bony segmented endocarp which remains closed I. Unripe indehiscent pods of Neltuma kuntzei with a thick pulpy mesocarp, these turning dark blackish-brown when ripe, reminiscent in colour to fruits of Anonychium. Photos courtesy of Marco Schmidt (A) (see Dressler et al. 2014), Dr. Omesh Bajpai and Dr. Lal Babu Chaudhary (B), Zeynel Cebeci (C) (https // en. wikipedia. org / wiki / Prosopis _ farcta), Dick Culbert (D) (see https // eol. org / pages / 640506, Colin Hughes (E, F, H, I), and Herta Kolberg (G) (see Plants of Namibia https // herbaria. plants. ox. ac. uk / bol / namibia).

Figure 8. The distributions of Indopiptadenia, Prosopis s. s., Anonychium, Xerocladia, Neltuma and Strombocarpa, based on 6,469 quality-controlled species occurrences from GBIF (www. gbif. org), DryFlor (www. dryflor. info), SEINet (www. swbiodiversity. org / seinet) and several other data sources (Ringelberg et al., in prep.). Map created using R packages ggplot 2 (Wickham 2016), sf (Pebesma 2018) and rnaturalearth (South 2017). The eight occurrence records, mapped in Bahia Brazil, are of Neltuma ruscifolia which is considered potentially native to that region (Burkart 1976 Oliveira & Queiroz 2020), while records of N. juliflora from Bahia, which is introduced and naturalised in that region, have been eliminated.