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Four new species of Xyris, X. ornithoptera, X. mallocephala, X. mentiens and X. porphyrea are described from Tanzania. Xyris ornithoptera is close to X. ednae Lock, X. mallocephala is Xyris sp. C sensu lock (1999), and X.mentiens and X. porphyrea resemble X. schliebenii Poelln. These new taxa confirm the general species-richness of south-western Tanzania and northern Zamhia.

Members of the genus Xyris are widespread in the area covered by Flora Zambesiaca (Botswana, Namibia (Caprivi Strip), Malawi, Mozambique, Zambia and Zimbabwe). They occur mainly in permanently or seasonally wet places, often on very nutrientpoor pale sandy soils, where they may be a prominent component of the vegetation. Their apparently simple structure and the general similarity between many of the species has led to difficulties in identification and a lack of understanding of the distribution of the taxa.

Two new species of Xyris are described from East Africa. They are Xyris ednae from Uganda and Xyris erosa from Tanzania. Xyris humpatensis var. rhodolepis is raised to specific rank as X. rhodolepis. The typification and status of X. anceps is discussed and two varieties distinguished. The typification and identification of X. welwitschii Rendle is examined. This name has been widely misinterpreted. It is here lectotypified, and a third new species, X. subtilis, described to accommodate Ugandan and Tanzanian material to which the name has been applied.

Plant perennial, slender, scabrid, caespitose, with bulbous bases, these covered by persistent chaffy-fibrous bases of old leaves. Roots slender. Stems short. Leaves erect to suberect, twisted and flexuous, 10-25 cm long, longer than the scape sheaths; blades 3-5 times longer than the sheaths, terete to obtuse-angled, narrowly linear, 0-7-1 mm thick, olivaceous; tips gradually narrowed, conicsubulate; sheaths ecarinate, multicostate, dull-brown to stramineous at base, downsheath gradually then abruptly dilating, the margins there long-ciliate, upsheath gradually converging, eligulate. Scape sheaths tubular, often open, dilated at apex, there short-bladed, toward base often reddish. Spikes severalflowered, many-bracted, ellipsoid becoming turbinate, 8-12 mm long, attenuate at base, red-brown; bracts spirally imbricate, strongly convex, the dorsal area narrowly oblong to lanceolate, pale, to 3 mm long, indistinctly medially 1-costate; sterile bracts several, oblong to obovate, 3-4 mm long, the inner ones broader and longer; fertile bracts several, obovate, 4 -5-5-5 mm long, ecarinate, finely irregularly toothed, the inner ones narrower, mostly oblong, more narrowly rounded, entire. Lateral sepals slightly curved, free, inequilateral, oblanceolate, c. 5 mm long, broadly acute; keel narrow, firm, ciliolate. Flowers not seen. Capsule lanceoloid, c. 4 -5 mm long, the placentation central. Seeds numerous, ellipsoid, c. 0 -5 mm long, apiculate, translucent, brownish, longitudinally multiribbed, finely cross-lined. (Fig. 1).

Critical examination of African Xyris in the course of revising the genus for the Second Edition of the 'Flora of West Tropical Africa' has yielded a number of interesting observations, including two new species. The identification of a large number of tropical African specimens has been linked with this revision and the need for a number of nomenclatural changes, which are included here, has arisen.