Abrus kaokoensis (Leguminosae-Papilionoideae-Abreae), a new species from Namibia

Abrus kaokoensis Swanepoel & H.Kolberg, a woody subshrub, is described as a new species. It is only known from the vicinity of the Kunene River and the Baynes Mountains in the Kaokoveld Centre of Endemism, Namibia. Its range is likely to extend into the botanically poorly explored adjacent mountainous parts of southwestern Angola. Illustrations of the species and a distribution map are provided. Probably most closely related to A. schimperi Baker, diagnostic characters of the new species include a suffrutescent habit and terminal elongated racemes with flowers clustered on appressed cushion-like reduced branchlets. A comparative table with diagnostic morphological characters to distinguish between the new species and A. schimperi is provided. © 2011 SAAB. Published by Elsevier B.V. All rights reserved.


Introduction
Hitherto the climber, Abrus precatorius L. subsp. africanus Verdc., was the only known member of this genus recorded for Namibia. It is widespread in sub-Saharan Africa and in Namibia is known from the central, northern and northeastern parts (Craven, 1999;Germishuizen and Meyer, 2003). In this contribution, a rare new species of Abrus is described from the Kaokoveld in northwestern Namibia. During a number of botanical expeditions to the region between 2005 and 2010, the authors independently encountered an unusual species of Abrus that grows as a subshrub near Swartbooisdrif (H. Kolberg) and in the Baynes Mountains (W. Swanepoel). These plants are here proposed as a distinct new species. The Abrus holdings in WIND revealed only one earlier collection of the new species (Bethune s.n.), filed under A. precatorius subsp. africanus. A specimen from the Kaokoveld in PRE, Merxmüller & Giess 30490, labelled Abrus cf. laevigatus, also belongs to the new species.

Phenology
Abrus kaokoensis was found flowering in March, following good rains.

Diagnostic characters
Abrus kaokoensis is probably most closely related to A. schimperi as both species are shrubs (not lianes) with terminal elongated inflorescences with woody pods and compressed seeds. It differs from A. schimperi in habit, as well as in characters of the leaves, inflorescences, flowers, pods and seed. A. kaokoensis is a subshrub, reaching a maximum height of 1 m, whereas A. schimperi is usually a much taller shrub, with a maximum height of about 3.6 m.
The leaves in A. kaokoensis are 4-8-jugate with the leaflets oblong, ovate-oblong, elliptic or narrowly obovate. In A. schimperi the leaves are 7-34-jugate and the leaflet shape is oblong or oblong-elliptic. The leaflet apex in A. kaokoensis is acute, rarely rounded and the base obtuse or subcordate and often oblique, whereas in A. schimperi the apex is always rounded and the base rounded to subacute. The leaflets differ furthermore in that they are usually much smaller in A. kaokoensis, only up to 16 × 8 mm, whereas in A. schimperi they reach double the size, up to 33 × 15 mm.
Differences in the floral characters include the inflorescences, which in A. schimperi can be much longer than in A. kaokoensis. The infundibular, lobed calyx in A. kaokoensis is considerably larger than the obconic, truncate or undulate calyx in A. schimperi. The corolla in A. kaokoensis is uniform in colour whereas the wings in A. schimperi usually are darker than the standard. Apart from the different shades of blue, mauve, violet or purple which the corollas of both taxa share, the corolla in A. schimperi may also be cream or yellow coloured.
In A. kaokoensis the pods are markedly smaller and thinner than in A. schimperi and lack the small tubercles that cover the surface of the latter. The seeds of the two taxa also differ; the usually larger, olive or yellow-green mottled seeds of A. kaokoensis are ellipsoid or obovoid in shape and the long axis is arranged at ± 30 degrees to the long axis of the pod. Seeds of A. schimperi are rounded-oblong or rhombic, brown with dark brown mottling and arranged with the long axis at right angles to the long axis of the pod.
Some of the more prominent morphological features to differentiate A. kaokoensis from A. schimperi are compared in Table 1.

Distribution and habitat
Abrus kaokoensis is known only from three localities (Fig. 2)   It seems likely that A. kaokoensis may also be found to occur in the adjacent botanically poorly explored mountainous parts of southwestern Angola. It may also prove to be more widespread in Namibia, in the rather inaccessible mountainous area bordering the Kunene River.

Conservation status
Although uncommon to rare and known from three localities only, Abrus kaokoensis is not threatened at present. Despite the plants in the Epupa and Swartbooisdrif areas being browsed by livestock, they otherwise seem healthy as with the Baynes Mountains population which is in an unpopulated area. Of concern, however, is the fact that very few flowers and pods were observed in the field. In addition very few young plants were seen and no seedlings at all. An investigation during March 2010, revealed that the flowers are wholly consumed by a species of blister beetle (Coleoptera-Meloidae) as soon as they are fully developed; to such an extent that only very few flowers survive to produce fruit and seed. In a population of about 40 plants in an area of 50 × 15 m, only the remains of 10 pods were found. Whether these pods produced any viable seed could not be established.

Etymology
The specific epithet refers to the Kaokoveld in northwestern Namibia, a region forming part of the Kaokoveld Centre of Endemism (Van Wyk and Smith, 2001). This biogeographically well-defined region extends into southwestern Angola.