Polygala sekhukhuniensis . (A) Flowering plant, showing habit of above-ground parts; (B) Mature leaf; (C) Flower, lateral view; (D) Flower, lateral view with wing-like sepal removed; (E) Old flower, lateral view with wing-like sepal removed to show capsule; (F) Ovary with style and stigma; (G) Androecium, showing staminal tube joined at base to two upper petals; (H) Seed. Voucher: Van Wyk 13031 . Scale bar 10 mm (A), 2 mm (B – E), or 1 mm (F – H). Artist: Daleen Roodt. 

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... the pioneering work of Wild (1965) on plants associated with soils rich in heavy metals and derived from ultramafic rocks in southern Africa, and subsequent ground- breaking research on plant-soil associations on southern African serpentinites by Morrey et al. (1989), Williamson et al. (1997) and Balkwill and Campbell-Young (2001), many plant species new to science have been described from such substrates. In recent years the Sekhukhuneland Centre of Plant Endemism (SCPE) in South Africa has been highlighted as an area harbouring potential new plant species (Van Wyk and Smith, 2001). Siebert et al. (2001) showed that the high levels of plant endemism of this region are significantly correlated with the heavy metal soils derived from ultramafic rocks. In the last three years, six new endemic plant species (including a new monotypic genus, Prototulbaghia ) were described from the SCPE (Venter et al., 2007; Vosa, 2007; Burrows and Burrows, 2008; Hankey et al., 2008; Retief et al., 2008; Manning and Goldblatt, 2009). Massoura et al. (2004) have shown that plant species adapted to heavy metal soils often accumulate or exclude metals that are present in the soil at high concentrations. This physiological adaptation is usually also expressed in the morphology through ecological speciation (Balkwill and Campbell-Young, 2001; Retief et al., 2008). Subsequent studies on heavy metal accumulation by plants in the SCPE by Mandiwana et al. (2007) have revealed several metal accumulators and excluders. Such species are known to be genetically different from their widespread congeners (Yang et al., 2005). This has warranted taxonomic investigation into one such excluder that is tolerant of soils rich in heavy metals, a member of Polygala that was initially considered an ecotype of P. leptophylla Burch. var. leptophylla . However, subsequent field work and comparative morphological studies have shown the putative ecotype to be a distinct new species related to members of section Polygala , subsection Heterolophus (Paiva, 1998), specifically P. hottentotta Presl., P. leptophylla var. leptophylla and P. seminuda Harv. It is confined to areas of highly water-dispersible soils derived from ultramafic rocks. The new species is here described as Polygala sekhukhuniensis Retief, Siebert & A.E.Van Wyk. This is the second excluder of heavy metals, after Euclea sekhukhuniensis (Retief et al., 2008), that is strictly confined to localized areas of naturally eroded, ultramafic soils in Sekhukhuneland. The aim of this paper is to describe and name the new taxon, and highlight the morphological, palynological and ecological differ- ences between the taxon and its most closely related congeners. Live material of the new species was extensively studied in the field. Its morphology was compared to existing descriptions and treatments of the genus (Exell, 1960; Paiva, 1998). Specimens of Polygala housed in the National Herbarium (PRE), Pretoria and H.G.W.J. Schweickerdt Herbarium (PRU), University of Pretoria, were examined to gather quantitative and qualitative data on morphology, phenology and distribution of the new species, as well as related taxa. Micrographs of seed were taken with a Nikon Digital Camera DXM 1200 F fitted on a Nikon SMZ 1500 stereomicroscope. Seed terminology follows Paiva (1998). Mature, unopened flower buds from herbarium specimens were dissected to obtain anthers with pollen. Unacetolyzed pollen grains were mounted onto aluminium stubs, sputter- coated with gold/palladium (Au/Pd) and examined with a FEI Quanta 200 ESEM Scanning Electron Microscope (SEM). Ten pollen grains per species were measured for polar length ( P ) and equatorial width ( E ). Palynological terminology follows Punt et al. (1994). Plant material of the new species and P. hottentotta , as well as soil samples were collected during early summer, environ- mental factors were noted and associated plant communities identified (Siebert et al., 2002). Samples were taken at ten sites, five each dominated by either species. Soil analyses was done with X-Ray Fluorescence (XRF) Spectrometry and plant analyses with Atomic Absorption Spectrophotometry (AAS) as well as Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). Terminology describing exclusion mechanisms follows Massoura et al. (2004). The subcosmopolitan family, Polygalaceae, comprises about 19 genera and 925 species (Mabberley, 1997). The flowers are superficially similar to those of members of the subfamily Papilionoideae (Fabaceae). However, the wings (alae) of Polygala flowers belong to the calyx and not to the corolla. The standard is completely different and Polygala has a crest at the tip of the keel. Currently various studies (Prenner, 2004; Banks et al., 2008) confirm the placing of the erstwhile order Polygalales in an expanded order Fabales (APG II, 2003). In the Flora of southern Africa region, the genus Polygala is represented by ± 88 species (Bredenkamp, 2000), of which ten are currently known from the SCPE. Polygala sekhukhuniensis Retief, Siebert & A.E.Van Wyk, sp. nov.; fruticulus pumilus caulibus patentibus caudice lignoso; Type. 2430 (Pilgrim's Rest): Mpumalanga, Thornecliffe Chrome Mine, turn off from Lydenburg-Sekhukhune road, [1 December 1997], Van Wyk 13031 (PRU, holo.; PRE, iso.). Rigid perennial shrublet, 0.2 – 0.4 m high, with a woody rootstock; stems and leaves sparsely adpressed-hairy; hairs unbranched. Stems usually more than four from rootstock, erect and spreading, branched, woody at base; young branches green, herbaceous. Leaves spirally arranged, shortly petiolate; petiole up to 0.75 mm long; blade linear-oblong or obovate, 7 – 15 × 1.0 – 2.5 mm, apex obtuse, occasionally acute, mucronate, margin entire. Inflorescences comprising terminal racemes, peduncle up to 80 mm long, pedicels 1.75 mm long. Flowers irregular; bisexual, drooping. Calyx pentamerous, with sepals unequal, three outer ones sepaloid, two inner ones petaloid, larger wing- like, 6 – 8 × 3.5 – 5.0 mm, all free; wings pink with darker pink veins. Corolla of five petals, lowest one forming a carina, crested, crest dark pink to purple, two lateral ones usually vestigial or absent, two upper ones joined at base to carina and staminal tube. Stamens eight, basally fused for ±two-thirds their length. Ovary superior, two locular. Fruit a laterally compressed capsule, up to 6.5 mm long, membranous, edges wing-like, 0.25 mm wide, deeply notched at apex, 2-seeded. Seed 4.5 × 1.5 mm, ellipsoid, caruncle oblique, appendages poorly developed, single one membranous, paired ones chitinous; indumentum silky white, ±1 mm longer than seed; testa dark-brown to black. Flowering time : November to June. (Fig. 1). Polygala sekhukhuniensis and two related species, P. hottentotta and P. leptophylla , are distinguished from P. seminuda and the rest of the genus by their narrowly ovate leaves, free anterior sepals, terminal racemes, wings not more than 6 mm broad, and the carina 6 mm long with crest 1 – 3 mm long. P. sekhukhuniensis and P. leptophylla differ from P. hottentotta , with the latter one having longer peduncles (124 mm versus 78 – 90 mm), greater number of flowers per raceme (23 versus 7 – 12), larger flowers (wing length 7.8 mm versus 6.8 – 7.0 mm), and smaller seed (4.3 × 1.5 mm versus 5.6 – 5.9 × 1.9 mm) (Table 1). Morphologically P. sekhukhuniensis most closely resembles P. leptophylla var. leptophylla , however, the leaf size of the former is 7 – 15 × 1 – 2.5 mm, whereas the leaves of the latter one are 14 – 22 × 1.5 – 3 mm (Table 1). Flowers of P. sekhukhuniensis differ from P. leptophylla var. leptophylla in the crest of the former being purple and the alae pink with darker pink veins, whereas the crest is white, pink or purple in the latter, with the alae whitish to yellowish with green veins. Seeds of P. sekhukhuniensis differ from P. leptophylla var. leptophylla in the colour of the testa, dark brown-black versus reddish-brown, the bare patch on the testa between the caruncle and the indumentum (the size, 0.3 × 0.6 mm versus 1.2 × 1.5 mm), and the caruncular appendages, poorly developed (0.2 versus 0.8 mm long) (Fig. 2; Table 1). Key to the species of Polygala in Sekhukhuneland In a review of Polygala palynological literature (Banks et al., 2008), no mention is made of descriptions, drawings, or micrographs of pollen belonging to the species compared in this paper. Hence, the SEM observations on pollen grains presented here are the first for the four taxa concerned (Fig. 3). Pollen of P. sekhukhuniensis is isopolar and spheroidal ...