Indigofera nigromontana is an indigenous shrub with wonderful horticultural potential, suited to any garden with a continental climate. Its foliage brings an unusual colour and a delicate texture to the screen planting, and when in flower it is exceptionally showy.
Indigofera nigromontana is a perennial, woody shrub of exceptionally good longevity, about 1–1.5 m high and 1–1.5 m wide. The hardwood stems are grey-brown and appear slightly cracked. It is multi-branched; many smaller branches appear as basal shoots; younger branches on the plant are light brown. Branches bear tufts of small, compound leaves with 3 silvery-grey to pale green leaflets. Some branches taper to spines but spines also appear randomly on the plant. These plants bear plentiful flowers mainly in spring during October. The flowers are small, mauve and pea-like. The seed appears after flowering from November to March. The seed pods are small, about 10–20 mm long and very narrow.
According to the assessors W. Foden and L. Potter, this species was assigned the status of Least Concern. Full assessments, however, are still to be conducted. It is traditionally considered a medicinal plant, so there could be a potential threat to the species due to the indiscriminate harvesting of muti plants but fortunately it is the stems and leaves that are used and not the whole plant and fortunately it is a widespread species.
Distribution and habitat
Indigofera nigromontana is widespread across the Northern Cape, Western Cape, Eastern Cape, Free State and also beyond the South African borders. Early collections of Indigofera nigromontana at Free State National Botanical Garden were found growing in wooded ravines, scattered in dolerite and sandstone outcrops and growing in stony soil. Later records described collections of this species in another similar area occurring in a semi-arid habitat; the plants were growing in full sun in shale soils. Collections made a few years later were found growing in poor soil, in full sun.
Derivation of name and historical aspects
Indigofera refers to the plant bearing indigo, a dye obtained from several species of this genus (Pooley 1998: 388). It is a large genus, comprising common and attractive perennial shrubs, undershrubs and annual herbs, with leaves often covered in hairs, sometimes lightly gland-dotted. There are around 730 species in this genus, 210 found in southern Africa (Leistner 2000: 286). The species epithet refers to the occurrence of the species in the Swartberg (Latin: niger = black, montanus = from the mountain), the epithet of the synonym I. spinescens refers to the presence of spines.
Indigofera nigromontana attracts butterflies and other insects with proboscises to the plant when in flower. The seed pods snap open spontaneously on ripening, thus dispersing the seed; this is characteristic of the pea family. The plant is well suited to drought. In very arid areas plants have very small and fewer leaves that are folded up. In cultivation, where plants are usually more accustomed to regular watering, leaves are more abundant and the shrub will thus appear slightly greener. This indicates that plant species can vary depending on their ability to adapt to their habitat, and that this is indeed an adaptable species. Indigofera nigromontana is a water-wise plant; this is indicated not only by its habitat of arid ridge veld but also by the green-grey foliage that reflects the sun's rays, and by the small leaflets and small stomata (minute pores in the surface of leaves) that reduce waterloss. The spines on the branches are also an adaptation to drought and help to reduce waterloss. These spines are not as obvious in cultivation as they are in their drier, natural habitat.
Uses and cultural aspects
Growing Indigofera nigromontana adds something special to a garden. It has a tendency to become straggly but if regularly or seasonally pruned or clipped it will keep a good shape. Pruning is advisable as it also has a tendency to become ‘top heavy'.
The abundance of pink/mauve flowers in spring is most striking and the soft grey-green leaves give the plant an attractive texture. It is highly recommended as a garden specimen.
Traditional Basotho knowledge refers to the plant as “Sefea-maeba” and “Mpepa”. It is claimed to be traditionally used for medicinal and magical purposes. “Sefea-maeba” refers to small leaves found in plants that are used to make a weak tea extract and “Mpepa' also refers to small leaves, butin plants that are generally used to burn as an incense to lift bad energy or to ensure happiness in the home (M.E. Raditlhare and T.S. Lekhetho, 2012 pers. comm.).
Growing Indigofera nigromontana
Growing Indigofera nigromontana from cuttings is not easy. Semihardwood cuttings were taken in summer but these were unsuccessful as they dried out very quickly. The greener tip cuttings initially appeared to be successful but also dried up in a few weeks. The growing medium used was a mixture of potting soil and river sand, and hormone powder was applied to the semihardwood cuttings.
Sowing seed is considered the best form of propagation, if you can find any (D. Human 2012, pers. comm.). Seeds of this species quickly disperse and the seed pods are quickly and easily parasitized. Pods also split open without warning and disperse the seed on impact, so gather the pods early or tie a stocking around the stem of ripening pods to catch the seed. Sow seed in summer from November to March.
Scarification is necessary when working with hard seeds with a hard testa or seed coat. To germinate Indigofera nigromontana seed the testa has to be cracked or chemically damaged to allow water through the hilum,a scar on the seed coat. Scarification can be mechanical, using a nail clipper to damage the seed coat, or chemically, such as letting the seed soak in sulphuric acid for 5 minutes (Zietsman 2012, pers. comm.).
Around the main plants growing in the Free State National Botanical Garden a few shoots have sprung up. These layered shoots can be transplanted but the success is also variable. The Free State Botanical Garden treasures six plants of this species that have survived for many years as garden specimens.
References and further reading
- Leistner, O.A. (ed.). 2000. Seed plants of southern Africa: families and genera. Strelitzia 10. National Botanical Institute, Pretoria.
- Pooley, E. 1998. A field guide to wild flowers of KwaZulu-Natal and the Eastern Region. Natal Flora Publications Trust, Durban.Venter, H.J.T. & Joubert, A.M. 1984. Climbers, trees and shrubs of the Orange Free State. P.J. de Villiers Publishers, Bloemfontein.
- POSA on www.sanbi.org.
Free State National Botanical Garden