Three new species of Zygophyllum ( Zygophyllaceae ) from Namibia and Northern Cape , South Africa

Three new species o f Zygophyllum L. from the lower Orange River area in Namibia and Northern Cape, South Africa are described, namely, Z app lanatum Van Zyl, Z. hirticaule Van Zyl and Z pterocaule Van Zyl.

Zygophyllum applanatum Van Zyl was first collected by Dinter during 1922Dinter during -1929, after which this tiny, but locally abundant plant, was missed by other collectors until recently.He recognised it as a new species and used the nom.nud.'adpressum' on herbarium sheet Dinter 6614 (BOL), whereas Schreiber (1963) considered this sheet to be a hybrid between Z. clavatum Schltr.& Diels and another Zygophyllum species with longer capsules.Subsequent collections and field observations made by me convinced me that Z. applanatum is a new species.Z. hirticaule Van Zyl was discovered by Oliver & Muller in 1976 and Z. pterocaule Van Zyl was first collected by Muller in 1977.Both Z. applanatum and Z. pterocaule belong to the subgenus Agrophyllum Endl.section Bipartita Huysst., with divided staminal scales as an Young stems of Zygophyllum species display taxonomically useful characteristics in cross section.In § Capensia, intemodes are often ventrally flattened, with or without lateral ridges, whereas § Alata is characterised by a distinct ventral groove (Van Zyl & Marais 1997).In § Bipartita the young stems of a few species are winged in a dorsiventral plane, usually with a single ventral wing.Z pterocaule displays both a dorsal and ventral wing.Figure 1.

Diagnostic characters
The most prominent features of Zygophyllum ptero caule are the suborbicular, simple leaves and young stems with two wings (hence the specific epithet which is Greek for winged stem).It is allied to Z. prismatocarpum Sond., also in section Bipartita, with regard to leaf and floral morphology, but differs in habit.Z ptero caule has a decumbent habit, reaching a height of only 0.15 m, whereas Z. prismatocarpum is an erect shrub of up to 1.0 m or more and has only one wing on its young stems.
Sterile Z. pterocaule could also be confused with Z. cordifolium L.f. ( § Paradoxa, subgenus Zygophyllotypus) because of simple, suborbicular leaves and a decumbent habit, but the presence of the two wings on the stems of the former species should, however, prevent confusion.The distribution of these two species some times overlap.When flowering, the small, 10 mm long, white flowers of Z. pterocaule should easily be distin guished from the larger.14-18 mm long, prominently marked, yellow flowers of Z. cordifolium.

Distribution and habitat
Z. pterocaule has a limited distribution in the lower Orange River basin (Figure 3A).On the Namibian side, collections were made at the Schakalsberge and between the confluence of the Boom and Dabimub Rivers with the Orange River.Collections were also made on Cornellskop and at Annisfontein.to the western side of the Richtersveld National Park in the Northern Cape.The vegetation on the South African side of the distribu tion area is classified by Hoffman (1996) as Lowland Succulent Karoo, occurring below the escarpment on rich soils derived from granite and gneiss, representing an extremely arid vegetation type.The dominant plants are dwarf shrubs belonging to the Mesembryanthemaceae.Rainfall varies from 50-200 mm annually during the winter months and summers are hot and dry.Irish (1994) describes the vegetation on the Namibian side as Namibian Succulent Karoo, characterised by chamaephytic dominance and a much lower rainfall than the Succulent Karoo ot South Africa.
Plants of this species were observed growing on limestone-rich, stony soils, on slight slopes and in dry stream beds, always in association with other Zygophyllum species.No shedding of leaves was observed possibly because, in this case, the leaves are succulent and serve as storage organs tor water.Flowering occurs from July to October while shedding of ripe seeds occurs months later.Ripening of lruits and seeds of Z. pterocaule takes longer than most other species in this genus because of the very succulent nature ot the truii.Although no graz ing damage to this species was observed, the small size of populations and the absence of seedlings or young plants were noticeable and therefore this species could be considered as vulnerable.Zygophyllum applanatum Van Zyl, sp.nov., ( § Bipartita), Z. clavato Schltr.& Diels affinis sed fruticulis prostratus, fructibus cylindricus.Figura 4.
Diels with regard to leaf and floral charac ters but is readily distinguishable by its fruits and habit.Z. clavatum has an erect habit, up to 500 mm high, whereas Z applanatum grows horizontally (hence the specific epi thet which is Latin for flattened or horizontally expand ed).During exceptionally good rainfall seasons Z applanatum can grow to 100 mm high by resprouting from the centre, so displaying an atypical habit.
Unfortunately the illustration (Figure 4), depicting this taxon was done from atypical material, giving a false impression of the habit.A photograph which was taken during an ordinary rainfall season (Figure 5), is included to remedy this.Both taxa have septicidal capsules but they differ in shape.Dried fruits of Z. applanatum are cylindrical, 5-angled and up to 1 2 x 4 mm, whereas those of Z. clavatum are wider than long, 5-partite, 2.5 x 4.0 mm.Z. applanatum with its limited distribution is restricted to the winter rainfall area, whereas Z clavatum occurs in a much larger area with both winter and summer rainfall, sometimes overlapping with the former species.

Distribution and habitat
Zygophyllum applanatum is found in a small area in the southern part of Namibia.Several collections were made around Luderitz, south of Aus and towards Witputz and Rosh Pinah (Figure 3A).The vegetation in this area is classified as Succulent Karoo Biome domi nated by chamaephytes (Irish 1994).Rainfall occurs during winter with occasional light snowfalls around Aus. Average annual precipitation varies from 40-90 mm, which is lower than the similar Succulent Karoo Biome in South Africa.Summers are hot and dry with frequent periods of drought.In the restricted areas belonging to the mining groups and where little or no farming activity occurs, populations consisting of hun dreds of plants, including many seedlings and young plants, were observed growing on chalky, desert flats often in association with other Zygophyllum species.Z. applanatum appears to be edible because in the sheep farming areas around Aus, plants were nearly absent inside grazing camps, whereas on the road shoulders they were common.Leafless plants were observed dur ing dry periods and it can be assumed that leaf shedding occurs as a survival strategy during droughts.Flowering and fruiting were recorded during August to December.The succulent nature of the fruits causes a delay in shed ding of ripe seeds and this usually occurs only months after flowering.Zygophyllum hirticaule Van Zyl, sp.nov., ( § Capensia), suffrutex multicaulis, a speciebus aliis sectionis ramulis pedunculisque hirsutis, fructo rubiginoso, alato tomentosoque distinguitur.Figura 6. Suffrutex multicaulis.Rami ebumei, ramuli hirsuti; internodia rotunda vel ventraliter complanata, sine costata.Folia sessilia; foliola glauca, obovata.Squama staminales simplices, ellipticae, margine et superficiebus ambatus in dimidio superiore papillatae, tomentosum, apice retuso.Fructus capsula loculicida, rubiginosa, oblonga, 5-angulata, lateribus tomentosis, alisque angustis, glabrescentibus.Semina arillo albo, testa madida mucum contentis prominantibus spiralibus procreans.Compact shrublet, branched from base, up to 0.3 m high and 0.5 m diam.Stems: old stems glabrous with swollen nodes and ivory-coloured bark; young stems hir sute, round in section or ventrally flattened but without lateral ridges.Leaves opposite, sessile, bifoliolate, glau cous when fresh, when dried, leathery in texture and dis playing numerous, embedded crystals resulting in an uneven, warty texture, glabrous to glabrescent on mar gins and at base; leaflets articulate, asymmetrical, obovate, 20-40(47) x 13-25(34) mm, apex rounded, base mostly cuneate; stipules fleshy, caducous, triangular or subrotund, margins fringed, tomentose on dorsal side, one on ventral side and one on dorsal side of stem, 2-3 x 3-6 mm.Flowers solitary or two together, axillary; pedi cel densely hirsute, up to 20 mm long.Sepals 5, ovate, tomentose on dorsal side, green, changing to burgundy when dry, persistent, 8 x 4-5 mm.Petals 5, patent, ellip tic to obovate, 10-13 x 5-8 mm, apex rounded or accuminate, base with short claw, pale yellow.Nectar disc fleshy, papillose, 10-angled.Stamens 10; filaments terete, 7-8 mm long; staminal scales 10, simple, oblong with a slightly rounded apex, margin and upper half of both surfaces papillate, 3.5-4.0x 1.5 mm, ± V2 as long as filament.Ovary oblong, 5-angled, tomentose with 5 glabrous wings, apex retuse; style terete; stigma simple.Fruit a loculicidal capsule with ± same shape when fresh or when dried; oblong, 5-angled and 5-winged, with red dish, tomentose sides and narrow, glabrescent wings, 13-17 x 11-13 mm.Seed oblong, in 2-3-seeded loculi, 4

Specimens examined
x 2 mm, brown with a white aril, testa smooth, translu cent, producing brown mucilage with prominent spiral inclusions when wet.

Diagnostic characters
Zygophyllum hirticaule is distinguished by its hirsute young branches and pedicels (hence the specific epithet which is Latin for hairy stems) and by the reddish, tomen tose capsule with narrow, glabrous wings.These fruits resemble those of Z debile Cham, in colour and shape but in the latter the indumentum is lacking.These two species occupy completely different distribution ranges.Z hirticaule stands somewhat on its own within section Capensia and has no close affinities with others in the group.

Distribution and habitat
Z hirticaule is found in the southwestern part of Namibia (Figure 3B).Collections were made around Witputz and Koike, N of Rosh Pinah.Irish (1994) classi fies the vegetation in this area as Succulent Karoo Biome characterised by chamaephytic dominance.Summers are hot and dry with frequent periods of drought.Rainfall occurs during winter months with a yearly average rang ing between 40 and 90 mm.Large populations were seen, including many seedlings and juveniles, growing on sparsely vegetated, stony, desert flats of a dolomitic and doleritic nature.A survival strategy, like so many species of this genus, seems to be the ability to shed leaves during periods of water stress.The remaining ivory-coloured stems of the leafless plants appear life less, but after the first rains they 'come alive' with leaves.Little evidence of grazing was seen and as farm ing activities in this area do not include ploughing, this species is at present under no threat.A specimen much resembling this species, but totally glabrous, was collect ed at Delphin kopf, Spencer Bay (Giess & Robinson 13206, WIND).This locality falls within a restricted mining area and in sandy desert terrain.For a final opin ion on this specimen, better field observation and more collections are necessary.

FIGURE 4
FIGURE 4 .-Zygophyllum applanatum .Van Zyl 44H2.A, flowering and fruiting branch, life size; B, twig with flower, leaf and young fruit; C, side-view of flower; D, sepals; E, petal; F, stamens with staminal scale, dorsal and ventral side; G, ovary; H, section o f ovary; I, range of leaves plus section; J, section of intemode; K, fresh fruit; L, section o f fresh fruit; M, dried fruit; N, section of dried fruit; O, seed.Scale bars; B -I, 8 mm; C -E , J-M , 4 mm; F-H , O, 2 mm.Artist: Inge Oliver.

FIGURE
FIGURE 5.-Zygophyllum applanatum Van Zyl.Photo taken during a normal rainfall sea son.