Vachellia tortilis

Overview

Salinity evidence comes from distinct materials: Mehari et al. tested seedlings of A. tortilis subsp. raddiana from Gezira, Sudan, with a first-week NaCl pulse followed by freshwater; Jaouadi et al. tested seeds collected at Bou Hedma, Tunisia and identified by the authors as A. tortilis subsp. raddiana var. ‘raddiana’ in a germination experiment. The first experiment's pulse concentrations are not four weeks of continuous root-zone salinity. [S1, S2]

Names and classification

The accepted name used here is Vachellia tortilis (Forssk.) Galasso & Banfi. Mehari et al.'s seedling salt experiment used material identified in the original paper as A. tortilis subsp. raddiana from Gezira, Sudan; Jaouadi et al.'s seed-germination study used seeds identified by the authors as A. tortilis subsp. raddiana var. ‘raddiana’, collected at Bou Hedma, Tunisia. Each experiment is described under its source's material and taxonomic scope; neither is generalized to the full species complex. [S1, S2, S6]

POWO treats Acacia tortilis (Forssk.) Hayne as a synonym of Vachellia tortilis and accepts V. tortilis subsp. raddiana. The experimental name is retained when describing the source study. [S1, S2, S6]

Morphology and identification

A thorny shrub or tree, often with an umbrella-shaped crown, bipinnate leaves, small pale flowers, and curved or twisted pods. Infraspecific variation and identification matter: the salt experiment discussed here used material identified as subsp. raddiana, not a sample representing the full species complex. [S1, S2]

Distribution, habitat and phenology

Species accounts from Africa and western Asia mainly describe dry to semi-arid woodland, savanna, and sandy sites; the cited sources do not document a georeferenced native salt marsh, salt lake, or saline-floodplain root-zone population. Table 2 of the Al-Saidi et al. (2006) proceeding cited by BiosalineDB gives cumulative germination by days 3–18 across 0.6–20 dS/m; by day 18, A. tortilis reached 94.0% at 0.6 dS/m and 26.0% at 20 dS/m. Table 1 reports leaf proline concentrations of 2.17±0.18, 2.92±0.36, and 4.67±0.27 μmol/g FW and leaf N of 3.69±0.03, 3.11±0.15, and 2.85±0.11% under sea-salt irrigation at 0.6, 6, and 12 dS/m. The short paper also describes a shadehouse trial with 540 one-year-old seedlings pooled across three species; it gives neither A. tortilis provenance nor species-specific seedling numbers, so this total does not establish a transferable dose–growth relationship for this species. [S1, S2, S3, S4, S6]

The available taxonomic and ecological sources do not provide a flowering or fruiting calendar that can be applied consistently; a single regional observation is insufficient to characterize the species. [S6]

Salinity in natural habitats

Native-range accounts chiefly describe arid woodland and savanna and do not document a specific population in saline root-zone habitat. The cited experiment tested a salt-water pulse in seedlings from one Sudanese subspecies provenance. [S1, S2]

Salinity studies

Mehari et al. grew two-month-old A. tortilis subsp. raddiana seedlings from Gezira, Sudan, in river-sand pots and compared 0, 150, and 300 mM NaCl. Salt water was applied four times on alternate days during the first week; plants then received fresh water daily to field capacity for three weeks. Stem and root relative growth rates, leaf shedding, and water potential were measured at four weeks. Growth-rate data remained available after the 150 and 300 mM pulses, but all leaves had been shed by week four, and the authors classified this material as sensitive under their criterion. Freshwater after the first week means the pulse concentrations were not continuous root-zone salinities. [S1]

Jaouadi et al. tested NaCl germination in seeds collected in August 2005 at Bou Hedma National Park, Tunisia, and identified as A. tortilis subsp. raddiana var. ‘raddiana’. Seeds were soaked in concentrated sulfuric acid for 1 h, washed in distilled water for 15 min, treated with Benlate for 1 h and rinsed, then placed in perlite-filled Petri dishes in darkness at 25 °C and watered daily with distilled water containing NaCl. The 30-day test recorded germinated seeds daily and measured germination percentage and mean germination time; Table 3 reports 21% germination at 22 g/L. This is a seed response from one collection site, not evidence of seedling or adult performance across the species complex. [S2]

Reported mechanisms and ecological adaptations

The study measured growth, water potential, and leaf drop, with freshwater flushing after the initial salt pulse as a key part of the design. The authors classified this Sudanese seed source as salt-sensitive under their criterion. The experiment does not support a mechanism inferred from continuous exposure. [S1, S2]

Conclusions and evidence gaps

The BiosalineDB “Tolerant” label gives no threshold. Tables 1–2 of the Al-Saidi et al. (2006) proceeding contain quantitative germination results for each of the three species and leaf proline and nitrogen data. Its shadehouse trial used 540 one-year-old seedlings across the three species but gives neither A. tortilis provenance nor species-specific seedling allocation, so it cannot establish a transferable dose–growth relationship or tolerance limit for this species. The Sudanese seedling-pulse and Tunisian seed-germination studies use different materials, salt systems, and life stages and cannot be combined into a single species threshold. [S1, S2, S3, S4]