The striking flowering spikes of Ecbolium tanzaniense photographed in the Kitonga Gorge, Tanzania.
Ecbolium tanzaniense Vollesen
Not formally assessed according to IUCN Red List criteria, but provisionally considered Near Threatened (NT) in this account.
Dry Acacia-Commiphora bushland and thicket on sandy soils and rocky hill slopes; sometimes found in open sandy areas.
A potential ornamental.
About this species
In common with most species of its genus, Ecbolium tanzaniense has a very unusual, livid- or turquoise-green flower. Together with its long, rope-like inflorescences with their overlapping bracts, this makes it a very striking species and an exciting find in the dry bushlands of central Tanzania. It is, however, rare and localised and was only recognised as a separate species as recently as 1989, having previously been treated as an odd form of the more widespread and common E. viride.
Very little is currently known about the pollinators of most species of Acanthaceae, but it would be of great interest to study the insects which are attracted to the very unusual flowers of Ecbolium.
Geography and distribution
Restricted to the dry, thorny bushlands of central Tanzania, where it has been found at 500–1,500 m above sea level, Ecbolium tanzaniense has a distribution almost identical to that of Barleria aristata, although it appears to be considerably less abundant. The central Tanzanian bushlands are known for their high numbers of rare and unique plant species.
Overview: Ecbolium tanzaniense is a shrub or shrubby herb up to 1 m tall. The young stems are greyish-green and largely hairless. The mature stems are woody with pale grey bark.
Leaves: The leaves have short stalks, and an elliptic blade 4–10.5 × 1.5–5 cm, with a rounded to attenuate base and acute to rounded apex. Both surfaces are hairless except for the hairy midvein above. The veins are prominent beneath.
Flowers: The flowers are held in long slender spikes, 6–23 cm long, at the ends of the branches or in the upper leaf axils, with numerous overlapping green bracts in four rows. The bracts are ovate, 12–20 × 8–16 mm, with a short, stiff, linear tip, and the upper bracts bear short glandular-hairs. The flowers are usually solitary and unstalked, each with a pair of short, narrow bracteoles, up to 3 mm long, at the base. The calyx is divided almost to the base into five equal, narrowly lanceolate lobes of 4–7 mm long. The flower emerges from between the bracts and is about 4.5 cm long and livid-green in colour; it has a very narrow cylindrical tube, about 2.5 cm long, and two lips. The upper lip is linear-lanceolate, curved backwards and is about 1.5 cm long. The lower lip is deeply divided into three lobes, the central lobe being about 2 cm long. The two stamens are attached at the base of the lower lip, the two-celled anthers being held beyond the tube. The ovary is short and hairless. The style is long and thread-like, the linear stigma being held beyond the flower tube.
Fruits: The fruit capsule is hairless or bears sparse minute hairs, and has two valves 18–24 mm long. It has a slender basal portion and then widens abruptly and becomes rounded in the upper portion to accommodate the seeds.
Seeds: The 2–4 seeds are disc-shaped and large (8–12 mm in diameter) with smooth or slightly bumpy surfaces and rim. They are held on long hooks which help to project the seeds from the capsule when it opens explosively.
Threats and conservation
Ecbolium tanzaniense is a rare species with a highly restricted range in central Tanzania. It is currently known from less than ten localities of which only the population recently discovered by Quentin Luke in the lowland portion of the Udzungwa Mountains National Park has any formal protection.
The main threat to this species is habitat degradation or destruction through human activity, as it appears to favour undisturbed sites. Perhaps its most important location is in the western Kitonga Gorge of the Great Ruaha River. This area is bisected by the busy Tanzania-Zambia highway which has inevitably resulted in local increases in human population, although the impact is low at present and much of the bushland there remains intact. The chief concern is that, in the absence of formal protection, this habitat will be gradually degraded or eroded away, which would be highly damaging to this species. Ecbolium tanzaniense is therefore best considered as Near Threatened (NT).
Steps towards the conservation of this species have already been taken through the collection of its seed for storage in Kew’s Millennium Seed Bank.
This striking shrub could have potential as an ornamental.
Millennium Seed Bank: Seed storage
Kew's Millennium Seed Bank Partnership aims to save plant life world wide, focusing on plants under threat and those of most use in the future. Seeds are dried, packaged and stored at a sub-zero temperature in our seed bank vault.
Number of seed collections stored in the Millennium Seed Bank: One
Millennium Seed Bank (MSB) collaboration
Ecbolium tanzaniense was one of several rare and/or threatened species for which seed was collected by the MSB Tanzania team and Kew botanists on a joint expedition in May-June 2008.
Acanthaceae seeds are notoriously difficult to collect because they are released quickly at maturity (by the explosive opening of the capsule, with the seeds being flung out by their hooks) and because of high seed predation rates by insects. We were therefore very pleased to collect this rare species.
The seed stored both in-country and in the Millennium Seed Bank at Wakehurst (in the UK) will help to safeguard the future of this global rarity.
This species is not currently in cultivation, but the closely related E. amplexicaule is currently on display in Kew’s Princess of Wales Conservatory, where it flowers regularly.
This species at Kew
Several specimens of Ecbolium tanzaniense can be found in the collection of pressed and dried specimens housed in the Herbarium at Kew, including the type specimen collected by former Kew botanist Sally Bidgood on her first botanical expedition to Tanzania in 1986. The details of this specimen, including images, can be seen online in the Herbarium Catalogue.
Vollesen, K. (1989). A revision of Megalochlamys and Ecbolium (Acanthaceae: Justicieae). Kew Bull. 44: 601–680.
Vollesen, K. (2010). Ecbolium. In: Darbyshire, I., Vollesen, K. & Ensermu Kelbessa (2010), Acanthaceae (part II). In: Flora of Tropical East Africa, ed. H. Beentje. Royal Botanic Gardens, Kew.
Kew Science Editor: Dr Iain Darbyshire
Kew contributors: Dr Kaj Vollesen (for sharing his expertise on this group; the description of the species given here is modified from that in his publications).
Copyediting: Emma Tredwell
Kew would like to thank the following contributors: The MSB Tanzania team from the Tanzania Tree Seed Agency in Morogoro, the University of Dar es Salaam, and the National Herbarium of Tanzania (which is part of the Tropical Pesticides Research Institute in Arusha) for their contribution to fieldwork in which seed of this species was collected.
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