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Barleria aristata is a member of the largely tropical Acanthaceae family and is one of 80 species of Barleria recorded from east Africa alone. Its beautiful blue flowers can be seen in abundance from late March to June along the Tanzania-Zambia highway where the road bisects the spectacular Kitonga (Ruaha) Gorge and the adjacent lowlands along the Lukose River in central Tanzania.

Barleria aristata

[KBu]

Darbyshire, I. (2008). New species in Barleria sect. Stellatohirta (Acanthaceae) from Africa. Kew Bulletin 63: 261. https://doi.org/10.1007/s12225-008-9028-8

Conservation
Although endemic to a small area of south-central Tanzania, this species appears to be locally common within its narrow range. It is particularly well known from sites along the Tanzania – Zambia highway, in the vicinity of the Ruaha Gorge. Here it is locally abundant and appears unthreatened despite its proximity to this busy route and the inevitable associated human activity. Large areas of woodland remain in this gorge system and the adjacent lowlands along the Lukose river and, as noted above, this species persists in areas of moderate disturbance and can even be locally dominant in such areas. It cannot therefore be considered threatened at present and is assessed as of Least Concern (LC) under IUCN (2001) criteria.
Diagnosis
B. taitensi similis sed foliis pro rata angustioribus, bracteis pro rata latioribus, apice bracteolarum aristato prominenti, lobo calycis antico profundius diviso, acumine lobi calycis postici longiore atque magis lineari praecipue differt.
Distribution
South-central Tanzania (Flora of Tropical East Africa regions T 5 – 7).
Ecology
Barleria aristata is recorded from dry bushland, typically on sandy, gravelly or rocky soils; 500 – 1200 m. It is most commonly associated with Acacia-Commiphora bushland, with supporting taxa such as Adansonia, Euphorbia, Cordyla, Albizia and Caesalpinia. In phytogeographical terms, it is distributed within the southernmost extension of the Somalia-Masai phytochorion (White 1983), an area with a high level of plant endemism (K. Vollesen, pers. comm.). It appears tolerant of some habitat disturbance, being recorded from denuded Acacia-Commiphora woodland in the Gulwe Valley (Carter et al. 2639) and being locally abundant along roadsides and in open, grazed woodland at the base of the Ruaha River Gorge and along the Lukose River (pers. obs.). It flowers principally at the end of the wet season and onset of the dry season, from March to June. Fruiting records from December to February in fact refer to specimens with persistent inflorescences from the previous year’s growth, the fruits having failed to develop fully or having been predated.
Morphology General Habit
Erect to scrambling subshrub, 30 – 200 cm tall
Morphology Leaves
Leaves subsessile or petiolate for up to 5 mm; blade narrowly ovate-elliptic to lanceolate, 3 – 8.5 cm long, 1 – 2 cm wide, base cuneate to acute, margin subentire, revolute when young, apex acute to subattenuate; upper surface with suberect golden long-armed stellate hairs, the paler stellate base often caducous leaving only the persistent arm, lower surface with dense whitish stellate hairs and with additional golden long-armed dendritic hairs along the margin and principal nerves to 2.5 mm long, longest and with a prominent bulbous base on the margin of the leaf base; lateral nerves (3 –) 4 – 5 pairs, impressed above when young, somewhat raised beneath
Morphology Reproductive morphology Flowers Androecium Stamens
Stamens 2, attached ± midway along the corolla tube; filaments 18 – 24 mm long, with short descending hairs in the lower 8 – 9 mm and with minute glandular hairs at the base, glabrous elsewhere; anthers 3 – 4 mm long
Morphology Reproductive morphology Flowers Androecium Staminodes
Staminodes 2 (– 3); lateral pair with filaments 1.2 – 1.6 mm long, pubescent; antherodes 0.25 – 0.75 mm long, thecae unequal; adaxial staminode, if present, minute, antherode absent
Morphology Reproductive morphology Flowers Calyx
Calyx 4-lobed; anticous lobe broadly subrhombic, 15 – 21.5 mm long, 8.5 – 11 (– 15) mm wide, base and apex attenuate, the latter bifid, segments ± divergent, aristate, 4 – 7.5 mm long, apices spinose, principal venation palmate, prominent, indumentum as bracts in the upper half, with sparse, predominantly simple hairs towards the base, these more numerous on the margin and within; posticous lobe with basal portion obovate, 6 – 7.5 mm long, 4 – 6.5 mm wide, apex caudate, 10 – 16 mm long, spinosely-tipped, principal venation parallel, upper half of narrow apical portion stellate-pubescent and with marginal bulbous-based long-armed stellate hairs, largely glabrous towards the base except for marginal simple hairs; lateral lobes subulate, 7 – 11 mm long, with minute subsessile glands towards the apex, elsewhere with numerous pale simple marginal hairs, longest and most dense towards the base, and with a dense basal ring of simple hairs around the disk
Morphology Reproductive morphology Flowers Corolla
Corolla (28.5 –) 35 – 41.5 mm long, blue (-purple) with a paler throat, finely pubescent towards the apex of the tube and on the lateral lobes of the limb outside; tube narrowly cylindrical, (12 –) 14.5 – 16.5 mm long, 2 – 2.5 mm wide centrally, pubescent within around the attachment of the stamens and along the fused extension of the filaments; limb 5-lobed, abaxial lobe split from the tube 2 – 4 mm before the remainder, each obovate, 15 – 22 mm long, the abaxial 9 – 15.5 mm wide, the lateral pair 8.5 – 13 mm wide, the adaxial pair 7 – 12.5 mm wide
Morphology Reproductive morphology Flowers Disc
Disk cupular, margin irregular, sparsely ciliate
Morphology Reproductive morphology Flowers Gynoecium Ovary
Ovary glabrous; style puberulous towards the base; stigma filiform, 1.3 – 1.8 mm long
Morphology Reproductive morphology Fruits
Capsule fusiform, laterally flattened, 13.5 – 16 mm long, 6.5 – 8 mm wide, apex shortly rostrate, glabrous
Morphology Reproductive morphology Inflorescences
Synflorescences terminating the principal and short lateral branches, conical or subglobose, 1.5 – 4 cm long; bracts with basal portion broadly obovate (-rounded), 9 – 11 mm long, 5.5 – 8 mm wide, apex aristate, (5 –) 6.5 – 10 mm long, curved outwards, spinose, outer surface of bract stellate-pubescent and with minute subsessile glands, with bulbous-based long-armed dendritic hairs to 3.5 mm long on the principal veins and margin and with additional short pale simple hairs towards the base and within; bracteoles with basal portion asymmetrically obovate to oblanceolate, 7.5 – 9.5 mm long, 2 – 4.5 mm wide, apex aristate, 4.5 – 7 mm long, spinose, indumentum as bracts
Morphology Reproductive morphology Seeds
Seeds discoid, 6.5 – 7 mm long, ± 6.5 mm wide, densely covered with buff hygroscopic hairs
Morphology Stem
Stems with dense buff to golden stellate hairs when young, some hairs with a dendritic base and a golden appressed-ascending arm; mature stems woody, bark pale grey
Note
Barleria aristata is a spectacular and highly distinctive new species which is unlikely to be confused. As such it is remarkable that it has remained undescribed until now despite its local abundance along one of the busiest routes in East Africa. It is clearly allied to B. taitensis S. Moore, a species with a disjunct distribution, occurring in south-eastern Kenya and north-eastern Tanzania (var. taitensis) and in Angola (var. occidentalis S. Moore). The more broadly based, abruptly aristate bracts and bracteoles of B. aristata however give a very distinctive appearance to the inflorescence lacking in B. taitensis, which has narrowly elliptic bracts and lanceolate bracteoles both lacking an arista. The calyx also differs significantly, with B. aristata having longer, narrower apical segments to the bifid anticous lobe (these 1.8 – 4.5 mm long in B. taitensis) and having a more abruptly narrowed posticous lobe with a long caudate apex (that of B. taitensis being gradually narrowed into an acumen). Vegetatively, the two species differ in B. aristata having proportionately narrower leaves with golden, not whitish, long-armed hairs on the upper surface, of which the stellate base is often early caducous in B. aristata but persistent in B. taitensis. B. aristata also displays a remarkable hair type on both the leaf margin and the inflorescence in which the dendritic base is swollen and bulbous. This character is absent in B. taitensis although similar hairs have been recorded from the more distantly related B. hildebrandtii S. Moore (Balkwill & Balkwill 1997). Finally, B. taitensis most often has white to pale blue flowers, with the tube usually 20 – 30 mm long. However, smaller, darker blue flowers are recorded in B. taitensis, particularly in the Angolan var. occidentalis and in the few specimens recorded from central Tanzania; these more closely resemble the flowers of B. aristata. The specific epithet “aristata” refers to the distinctive aristate bracts and bracteoles, a principal diagnostic character of this species.
Type
Tanzania, 17 km on Kitonga – Morogoro road, Bidgood, Darbyshire, Hoenselaar, Leliyo, Sanchez-Ken & Vollesen 5027 (holotypus K!; isotypi BR!, CAS!, DSM!, EA!, MO!, NHT!).

[KSP]

Kew Species Profiles

General Description
A spectacular blue-flowered undershrub, Barleria aristata was first described relatively recently, despite its abundance along one of the main transport routes in east Africa!

Barleria aristata is a member of the largely tropical Acanthaceae family and is one of 80 species of Barleria recorded from east Africa alone. Its beautiful blue flowers can be seen in abundance from late March to June along the Tanzania-Zambia highway where the road bisects the spectacular Kitonga (Ruaha) Gorge and the adjacent lowlands along the Lukose River in central Tanzania.

It forms dense thickets in the undergrowth of the dry thornbush and along the roadsides, brightening the journey along this busy route. However, in global terms, this is a rare and highly restricted species that was given a scientific name for the first time as recently as 2008.

Species Profile
Geography and distribution

This species is restricted to a small part of central Tanzania. This region falls within the rain shadow of the Eastern Arc Mountain chain which, together with the sandy soils typical of the area, results in very dry growing conditions and a thornbush vegetation dominated by Acacia and Commiphora trees, and with sparse ground cover. 

The central Tanzanian bushlands are known for their high numbers of unique plant species. Indeed, Barleria aristata is just one of four Barleria species unique to the region, the others being B. granarii , B. pseudosomalia and B. subregularis , all of which have only been described as new to science in the last three years by Kew botanist Dr Iain Darbyshire.

Description

Overview:  Barleria aristata is an undershrub up to 2 m tall, the vegetative parts being covered in golden, star-shaped (stellate) hairs. The mature stems are woody with pale grey bark.

Leaves:  The leaf stalks are absent or short, and the leaf blade is narrowly elliptic or lance-shaped, 3-8.5 × 1-2 cm, with 4 or 5 pairs of lateral veins impressed on the upper surface and prominent beneath.

Flowers:  The flowers are held in dense conical or near-globose heads, 1.5-4 cm long, at the ends of the branches. The bracts are broad, with a long, slender, curved tip ending in a spine. The paired bracteoles are similar but narrower. The calyx is divided almost to the base into four highly unequal lobes. The front lobe is broad and elliptic or rhomboid in shape, 15-22 × 8-11 mm, and narrows into a pair of divergent spiny tips. The back lobe has a short, broadened base, 6-8 × 4-7 mm, before narrowing into a long, slender tip, 10-16 mm long, ending in a sharp spine. The two lateral lobes are 7-11 mm long and very slender. The flower is 35-42 mm long and blue or blue-purple with a paler throat. It has a narrowly cylindrical tube, 14-17 mm long, before dividing into 5 large lobes, the lowermost splitting from the tube slightly earlier than the remainder, each lobe being 15-22 mm long. The two white stamens are attached midway along the corolla tube, the anthers being held beyond the tube. There are also two (rarely three) minute staminodes less than 2 mm long and hidden within 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 is a hairless capsule with two valves, elliptic in face-view, and flattened laterally with a short beak. The two seeds are disc-shaped and are covered in long, silky hairs. They are held on long hooks which help to project the seeds from the capsule when it opens explosively.

This species is typical of section Stellatohirta of the genus Barleria , in which the species all share the complex star-shaped hairs, the dense globose to spike-like flower-heads and the two-seeded capsules with silky-haired seeds. The genus as a whole is easily recognised by its unusual 4-lobed calyx, of which the front and back lobes are usually much broader than the lateral pair.

Threats and conservation

Barleria aristata has a very restricted range and is globally rare, with only two main population centres, one in the Kitonga Gorge-Lukose River area and one further north in the vicinity of Mpwapwa. However, it can be locally abundant or even dominant in the understorey and appears tolerant of moderate habitat disturbance, being able to withstand grazing pressure and apparently being at home along roadsides.

The busy Tanzania-Zambia highway has inevitably attracted local increases in human population in the Kitonga-Lukose area but human impact is stable at present and much of the bushland remains intact. While this species is therefore currently considered to be of Least Concern (LC), any future increase in the scale of habitat loss would quickly render it vulnerable.

The main populations are not covered by any formal conservation measures at present, although Barleria aristata has been recorded from the lowland portion of the Udzungwa Mountains National Park.

Uses

As with many species of Barleria , the striking flowers of B. aristata have high horticultural potential, yet only a few Barleria species are widely cultivated. They are said to be susceptible to disease.

Millennium Seed Bank: Seed storage

Barleria aristata is not currently represented in any seed bank. Attempts were made by the Millennium Seed Bank Tanzania team and Kew botanists to collect seeds in June 2008 but, as with many Acanthaceae species, high levels of seed predation and difficulties in finding mature seeds meant that insufficient quantities of viable ones could be collected.

Cultivation

Like many species in the genus, Barleria aristata has high horticultural potential, though it is not currently known to be in cultivation.

This species at Kew

Barleria aristata is well-represented in the collection of dried, pressed specimens housed in the Herbarium at Kew, which includes the type specimen collected by a Kew-led expedition to Tanzania in March 2006. The details of this specimen can be seen online in the Herbarium Catalogue. The oldest known collection of B. aristata dates back to 1925, and was collected by the German railway worker and prolific plant collector (Gustav) Albert Peter.

Distribution
Tanzania
Ecology
Dry bushland, typically of Acacia-Commiphora trees, on sandy, gravelly or rocky soils.
Conservation
Least Concern (LC) according to IUCN Red List criteria. Not currently considered threatened.
Hazards

None.

[KSP]
Use
A potential ornamental.

Native to:

Tanzania

Barleria aristata I.Darbysh. appears in other Kew resources:

Date Reference Identified As Barcode Type Status
Bidgood, S. [5027], Tanzania K000190255 holotype

First published in Kew Bull. 63: 261 (2008)

Accepted by

  • Darbyshire, I., Vollesen, K. & Kelbessa, E. (2010). Flora of Tropical East Africa, Acanthaceae (Part 2): 287-756.

Literature

Kew Bulletin

  • Balkwill, M.-J. & Balkwill, K. (1997). Delimitation and infra-generic classification of Barleria (Acanthaceae). Kew Bull. 52: 535 – 573.
  • Balkwill, M.-J. (1998). Barleria Sect. Stellatohirta. p. 110. In: M.-J. Balkwill & K. Balkwill, A preliminary analysis of distribution patterns in a large, pantropical genus, Barleria L. (Acanthaceae). J. Biogeogr. 25: 95 – 110.
  • IUCN (2001). IUCN Red List Categories and Criteria. Version 3.1. IUCN Species Survival Commission, IUCN, Gland, Switzerland and Cambridge, UK.
  • Moore, S. le M. (1911). Alabastra diversa. Part XXI. Acanthaceae Africanae novae. J. Bot. 49: 293 – 298 & 305 – 313.
  • White, F. (1983). Vegetation of Africa. A descriptive memoir to accompany the Unesco/AETFAT/UNSO vegetation map of Africa. Unesco, Paris, France.

Kew Species Profiles

  • Balkwill, M.-J. & Balkwill, K. (1997). Delimitation and infra-generic classification of Barleria (Acanthaceae). Kew Bull. 52: 535–573.
  • Darbyshire, I. (2008). New species in Barleria sect. Stellatohirta (Acanthaceae) from Africa. Kew Bull. 63: 261–268.
  • Darbyshire, I., Vollesen, K. & Kelbessa, E. (2010). Acanthaceae (part II). In: Flora of Tropical East Africa, ed. H. Beentje. Royal Botanic Gardens, Kew.
  • Jex-Blake, A.J. (ed., 1957). Gardening in East Africa: a practical handbook. Fourth edition. Longmans, Green & co., London, New York.

Herbarium Catalogue Specimens
Digital Image © Board of Trustees, RBG Kew http://creativecommons.org/licenses/by/3.0/

Kew Backbone Distributions
The International Plant Names Index and World Checklist of Selected Plant Families 2021. Published on the Internet at http://www.ipni.org and http://apps.kew.org/wcsp/
© Copyright 2017 World Checklist of Selected Plant Families. http://creativecommons.org/licenses/by/3.0

Kew Bulletin
Kew Bulletin
http://creativecommons.org/licenses/by-nc-sa/3.0

Kew Names and Taxonomic Backbone
The International Plant Names Index and World Checklist of Selected Plant Families 2021. Published on the Internet at http://www.ipni.org and http://apps.kew.org/wcsp/
© Copyright 2017 International Plant Names Index and World Checklist of Selected Plant Families. http://creativecommons.org/licenses/by/3.0

Kew Science Photographs
Digital Image © Board of Trustees, RBG Kew http://creativecommons.org/licenses/by/3.0/

Kew Species Profiles
Kew Species Profiles
http://creativecommons.org/licenses/by-nc-sa/3.0