Zilla spinosa (L.) Prantl
Bunias spinosa L.
Eng.: Spiny zilla. Spa.: Zilla. Fre.: Zilla. Ara.: Zilla, silla, besilla, bseilla, basilla, shagaret el-hommoos, ommo, nuggir, achfud, chebreg, chabrègue. Tam.:/Tamahaq: Aftezzen, aftazzan, ftozzer, chebraq.
Shrub or subshrub, deciduous, hermaphrodite, up to 1.5(2) m in height, very ramose from the base, hemispherical in shape, very spiny. Stems and branches upright, with whitish bark, branchlets glaucous. Spines straight, rigid. Leaves alternate, highly variable in size: those in the centre of the shrub very large —up to 15(20) cm—, external leaves much smaller; ovate-oblong or linear in shape, with entire margin, slightly fleshy, glaucous, glabrous, sessile or subsessile, promptly caducous. Inflorescences in sparse terminal racemes. Calyx with 4 sepals 7-9 mm, unequal, the 2 outer sepals linear-oblong and the 2 inner sepals oblong-lanceolate, green or violet. Corolla with 4 petals 19-20 mm, ovate or ovate-oblong, longly unguiculate, purple. Stamens 6. Fruit an indehiscent silicle 6-12 mm long, ovoid, subglobose, ending in a long tip, with or without wings according to the subspecies. Seeds 2, ellipsoid, reddish-blackish, almost smooth surface.
Flowering:
February to May.
Fruiting:
May to July.
Habitat:
Rocky steppes and slightly sandy deserts, from sea level to 2,500 m.
Distribution:
Saharo-Arabian (see further details below).
Observations:
In North Africa there are 4 subspecies which are fairly well differentiated by the silicle, which can be smooth or with protuberances, wings.
Z. spinosa subsp. spinosa (Z. myagroides Forssk., Z. microcarpa
Vis.), does not have any conspicuous appendages on the fruit and grows in the eastern Sahara (Libya and Egypt) and Asia Minor.
Z. spinosa subsp. costata Maire & Weiller has carinate adult silicle, without wings; it grows in the southern areas of central and western Sahara, reaching in the E to Libya; it has not been cited in neither Tunisia nor Egypt.
Z. spinosa subsp. biparmata (O.E.Schulz) Maire & Weiller, with apophysis, wings on the fruit; this plant is described and cited in Libya and Egypt; its presence in Tunisia is doubtful.
A very similar taxa, perhaps a synonym, is Z. spinosa subsp. macroptera (Coss.) Maire & Weiller (Z. macroptera Coss.), which has a silicle with 2 longitudinal wings surrounding the base, appearing to have 4 wings, one at each corner; endemic to the western region, distributed through the drier eastern and southern slopes of the High Atlas, Anti-Atlas, Saharan Atlas, northern-western and central Sahara.
Conservation status:
Common and widely distributed species. Currently, it has not been assessed at a global level in the IUCN Red List of Threatened Species. In the Red List of vascular plants of Egypt (Flora Aegyptiaca Vol 1, 2000) subsp. biparmata is listed as “Vulnerable”.