Barleria rigida Willd. ex Nees

Darbyshire, I., Tripp, E.A. & Chase, F.M. (2019). A taxonomic revision of Acanthaceae tribe Barlerieae in Angola and Namibia. Part 1. Kew Bulletin 74: 5. https://doi.org/10.1007/s12225-018-9791-0

Type

“Africa australi extratropical”, without specific locality, without date, Hoffmannsegg in herb. Willdenow 11660 (lectotype B-W* [B-W11660-010], selected here). Additional original syntypes: South Africa, Grootriviers Poort, fl., without date, Burchell 1991 (syntype G-DC, isosyntype K! [K000794967]); Grootriviers Poort, Lichtenstein s.n. (syntype B, presumed †).

Morphology General Habit

Spiny shrublet, 5 – 45 cm tall, much-branched, leafy stems erect, spreading or trailing; stems retrorsely white-puberulent mainly or exclusively in two opposite-decussate bands, nodes often strigose

Morphology Leaves

Leaves rather coriaceous, blade variable, broadly oblong to narrowly oblong-elliptic or -lanceolate, 0.8 – 4.3 × 0.2 – 1.1 cm (l:w ratio 1.6 – 6.9:1), base cuneate or truncate, margin white-cartilaginous, sinuate, with or without marginal spines, these can be harsh and up to 4 mm long, apex acute and apiculate or spinose, surfaces glabrous or sparsely yellow-strigose at least along the midrib beneath, sometimes also minutely puberulent when young; lateral veins indistinct, midrib prominent beneath; petiole 0 – 5 mm long

Morphology Reproductive morphology Inflorescences

Inflorescences axillary, contracted unilateral cymes 1 – 2.5 cm long in the upper axils, each 2 – 10-flowered or flowers solitary; bracteoles green with white margin and midrib or whitish throughout, linear-lanceolate or lanceolate, 10 – 29 × 1 – 6 mm, base cuneate or parallel, margin with 2 – 18 spines per side of variable length (see varieties) or margin rarely entire, apex long-spinose

Morphology Reproductive morphology Flowers Calyx

Calyx ± coriaceous, at first pale green to brown-green or pinkish, often with whitish margin and base, sometimes also with contrasting darker venation, sometimes later turning whitish throughout; anterior lobe elliptic, (oblong-) ovate or lanceolate, 9.5 – 22 × (3 –) 3.7 – 9 mm, base attenuate, margin with (1 –) 3 – 20 lateral spines per side 0.2 – 5.7 mm long ending in a stiff bristle, apex spinose or bifidly so, surface sparsely strigose and sparsely puberulent or glabrous, palmate-reticulate venation ± prominent; posterior lobe as anterior lobe but 10 – 28.5 × (3.2 –) 4 – 9.5 mm, apex attenuate into a long spine; lateral lobes linear-lanceolate, 5.5 – 11 mm long

Morphology Reproductive morphology Flowers Corolla

Corolla 25 – 38.5 mm long, white, pink, pale blue or violet, pubescent externally with mixed glandular and eglandular hairs or rarely only eglandular hairs; tube 15 – 22 mm long, cylindrical, narrowly campanulate towards mouth; limb subregular; abaxial lobe obovate (-elliptic) 8 – 16 × 6.5 – 11 mm, apex rounded or emarginate; lateral lobes as abaxial lobe but 8 – 14 × 5 – 8.5 mm; adaxial lobes 8.5 – 15 × 4 – 8 mm

Morphology Reproductive morphology Flowers Androecium Stamens

Stamens rather long-exserted, inserted at or shortly above midway along corolla tube; filaments 16.5 – 24 mm long; anthers 1.4 – 2.6 mm long; lateral staminodes 1 – 2.7 mm long, pubescent at base, antherodes 0.3 – 0.9 mm long

Morphology Reproductive morphology Flowers Gynoecium Ovary

Ovary with a ring of minute crisped white hairs at apex and extending onto style base; stigma clavate or subcapitate, 0.3 – 0.7 mm long, apex bilobed

Morphology Reproductive morphology Fruits

Capsule 4-seeded, 9.5 – 15.5 mm long, glabrous; seeds 3.7 – 4.2 mm long and wide.

Note

Barleria rigida is one of the most widespread and variable species of Barleria in Namibia and, together with B. irritans Nees and B. bechuanensis C. B. Clarke from South Africa, forms a difficult species complex that has recently been revised by F. Nyirenda and K. Balkwill at the University of the Witwatersrand (J herbarium). Nyirenda (2012) has proposed several new species in this group, but this revision has not yet been effectively published. Within plants previously recognised as B. rigida sensu lato, she splits the Namibian B. schenckii Schinz as a distinct species (although she appears to have overlooked this name and proposed the new species B. bracteilobis in its place — see sp. 6 below) and recognises three varieties within B. rigida. We largely follow this approach here, although (1) we note that the amount of geographic overlap between the varieties is rather minimal and they may be better treated as subspecies; (2) our delimitation of the varieties, and the identification of some of the specimens differs slightly from Nyirenda’s (2012) work; and (3) we recognise one further, highly range-restricted variety in southern Namibia. These varieties are delimited primarily by variation in leaf, bracteole and calyx morphology including their spine systems, and in the number of flowers per inflorescence. Whilst most specimens are fairly easy to place in one of the four varieties using the key below and comparison to named specimens, there are occasional intermediate populations, particularly where the ranges meet. Barleria schenckii could be treated as a further, extreme variety but it is considered to be sufficiently discrete that it is best treated as a vicariant species.