Indigofera articulata Gouan
I. tinctoria sensu Forssk., I. glauca Lam., I. argentea L.
Eng.: Indigo. Spa.: Índigo. Fre.: Indigotier. Ara.: Nila, nîla, neela, sabagha (Hassanía). Tamahaq: Laema, afaïsawa.
Shrub, up to 1.5 m in height, often highly branched and silvery in overall appearance. Leaves opposite, imparipinnate, with (1)3-5 leaflets, 1-2.5 × 1-1.8 cm (terminal leaflet larger), opposite, obovate, with rounded apex, greyish-silvery on both sides. Inflorescences in axillary racemes, subsessile, shorter than the axillary leaf, with 10-20 flowers. Calyx 1.5 mm, with triangular teeth of the same length as the tube. Corolla 3-4 mm, papilionoid, yellow or golden, with standard with a brown patch, pubescent on the dorsal side. Androecium monadelphous. Pods 0.7-1.3 × 0.3-0.4 cm, linear, arched upwards, lomentaceous and with globular segments, brown, ± silky, with 2-4 seeds.
Flowering:
February to April.
Fruiting:
May to July.
Habitat:
Sandy plains and edges of fields where it behaves as a ruderal species.
Distribution:
Algeria (Ahaggar , around Tamanrasset), Egypt, Sudan, Djibouti, Ethiopia, Somalia, Arabia.
Observations:
A closely related species is I. coerulea Roxb., but leaves also opposite, with (5)7-9 leaflets, glabrous on the upper side, and pods only slightly lomentaceous, with cylindrical-ovoid segments. It grows along rocky fields and wadis. In North Africa it is found from SE Egypt up to Ethiopia and Somalia, further to the E it is found in the Arabian Peninsula up to India and Sri Lanka.
Another species smaller in size is I. argentea Burm.f. [I. semitrijuga Forssk. var. tetrasperma DC., I. arenaria A.Rich. var. strigosa N. Terracc.] (Ara.: Afalanjiat, nela baladi. Tamahaq: Isoersoem, awudeni, isaersam). Subshrub, 20-50 cm in height, covered by a silvery tomentum with scattered glandular hairs c. 0.5 mm. Stems usually ascending. Leaves imparipinnate, with rachis and petioles 0.5-1 cm, and with 5-7 leaflets, 2.5-6 × 2-3 mm, opposite, obovate-cuneate, pubescent-silvery on both sides. Inflorescences in lax racemes, with 4-10 flowers, usually longer than the axillary leaf. Calyx c. 2 mm, densely pubescent. Corolla 4-5 mm, papilionoid, bright red, with standard pubescent on the outside. Pod 1-1.2 cm, straight and ± lomentaceous, with glanduliferous hairs, and 3-5 seeds. It grows in sandy plains, in tropical and subtropical climate, from western Sahara to India. In North Africa it is found at least in Egypt and Algeria, with unconfirmed presence in Morocco and between Libya and Chad (in the Tibesti).
Another similar species is I. arabica Jaub. & Spach, a perennial herbaceous plant 15-30 cm, only woody at the base, with pubescent silvery stems. Leaves imparipinnate, with 3-5 leaflets, often opposite, with pods 0.5-1.1 × 0.3 cm, flat, pubescent, silvery, with 2-5 seeds. It grows in rocky wadis, seasonal desert river beds, rocky or sandy, in Egypt, Sudan, Eritrea, Ethiopia, Somalia, and the Arabian Peninsula.
Conservation status:
Relatively common and widespread species, not considered threatened. Currently, they have not been assessed at a global level in the IUCN Red List of Threatened Species. In the Red List of vascular plants of Egypt (Flora Aegyptiaca Vol 1, 2000) I. coerulea is listed as “Rare” and I. argenteas as “Vulnerable”.