Barleria aristata I.Darbysh.

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

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.

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!).

Morphology General Habit

Erect to scrambling subshrub, 30 – 200 cm tall

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

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 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 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 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 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 Seeds

Seeds discoid, 6.5 – 7 mm long, ± 6.5 mm wide, densely covered with buff hygroscopic hairs

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.

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.

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.

Use

A potential ornamental.