Thesium quartzicolum Zhigila, Verboom & Muasya, 2019

Zhigila, D. A., Verboom, G. A., Stirton, C. H. & Muasya, A. M., 2019, A taxonomic revision of Thesium section Hagnothesium (Santalaceae) and description of a new species, T. quartzicolum *, South African Journal of Botany 124, pp. 280-303 : 301-302

5.2.2.7. Thesium quartzicolum Zhigila, Verboom & Muasya sp. nov.

Type: South Africa, Overberg, Western Cape, Bredasdorp Division (3420), Spitskop farm (-BC), (34̊18′5.91″S and 20̊17′5.90″E), on quartz patches in renosterveld vegetation, 22 March 2017, ♂ & ♀ plants Zhigila & Muasya 026, ( BOL, holotype!; K!, NBG!, PRE!, isotypes) .

An erect annual herb, 8–15 cm tall, heath-like, yellowish to golden-green in appearance, plant brittle, with a fibrous rootstock, scarcely branched, 3–10 jointed branches, branching pattern virgate, leaves subtending branchlets present. Stems woody at base, herbaceous above, 1–3 mm in diameter, erect, glabrous, terete in transverse section. Leaves sparingly distributed and reduced to scales, decurrently adpressed to the stem, golden-green, tomentum glabrous, no prominent venation or midrib, leaf apex subacute to obtuse, margin cartilaginous and ciliolate, straight. Midrib not visible, glabrous, fleshy, apex obtuse to subacute, In fl orescences distributed along the branch length, in branchlet axils, spikes, sessile or attached to the stem by a short to non-existence pedicel; bracts and bracteoles scale-like; bracts fleshy, 0.8–2.5 × 1–2 mm, broadly subrotund, margins cartilaginous, acute at tips, much shorter relative to the flower length, usually adpressed; bracteoles bract-like but smaller, 0.7–2.5 × 0.5–1.5 mm; flower shape campanulate, green to golden green, 3–5 × 2–4 mm, 4-merous, external gland between perianth lobes absent, perianth lobe segments 2–3.5 × 1–2.5 mm, ovate to lanceolate, obtuse at tips, rarely acute, not distinctly uncinate, not lobulate; tube short, 0.2–0.3 mm long. Male plants similar to female counterpart. Male plants: branches slender and sparingly arranged along the stem length, internodes 3–6 mm; leaves lax, not imbricate, broadly ovate to triangular, 1–2 × 0.5–0.8 mm; inflorescences lax; hypanthium tube conspicuous, shorter than perianth lobe tubes; stamen tetramerous, never pentamerous, staminal filaments distinct to connately exserted at junction of hypanthium and perianth lobe tubes, about 0.2 mm. Female plants are stouter and branches woodier than in male plants, internodes 4–8 mm; leaves lax, not imbricate, broadly ovate to triangular, 0.5–1.5 × 0.5–0.8 mm; inflorescences lax; hypanthium tube shorter than the perianth tubes; style about 0.3 mm tall. Fruits nutlets, ovoid to globose, green to golden-green, elaiosome absent, 1.2–3 × 1–2.5 mm, without ribs, veins inconspicuous, capped with green persistent perianth lobe remnants, shorter than fruit length ( Fig. 10 ).

5.2.2.7.1. Diagnostic features. Thesium quartzicolum is similar to T. fragile with which it shares features such as growth form, plants brittle, heath-like, branching pattern virgate, male and female similar, leaves scanty, scale-like, subtending each branchlet, and few-flowered spikes. It has several striking morphological features distinguishing it from T. fragile , e.g., erect annual herb to about 8–15 cm tall (versus erect perennial suffrutex, 10–40 cm tall), rootstock slender (versus woody), stems terete, about 2 mm thick (versus sulcate or subangled, 2–4 mm thick), fruits globose to ovoid, golden-green, sessile without elaiosome (versus truncated), perianth segments green, persistent (versus perianth remnants white, yellow or orange), usually found on silcrete-quarzitic soils (versus normally found in sandy coastal areas).

5.2.2.7.2. Distribution and habitat. Thesium quartzicolum is a narrow endemic restricted to the silcrete-quartz outcrops of the typical renosterveld scrub of the Overberg ( Fig. 7E , solid triangles) and known from three localities at elevation between 200 and 300 m.

5.2.2.7.3. Etymology. The specific epithet means ‘quartz dwelling’ and alludes to its preference for the quartzite soils of the Overberg renosterveld.

5.2.2.7.4.Conservation status. Although concerted efforts to find more populations were made, no other populations have been found. Therefore, further botanical surveys should be conducted to explore whether more populations exist. Potentially, its geographical range is restricted to the renosterveld quartz patches of the Overberg. These patches are considered as one of the Critically Endangered habitats ( Raimondo et al., 2009) as 95% of the landmass is under cultivation ( Curtis et al., 2013; Curtis, 2017). Also, large mammals graze on T. quartzicolum (Zhigila pers. obs.), possibly having negative impacts on its population given that remnant Renosterveld patches are used for livestock rearing. Hence, as T. quartzicolum is endemic to Overberg Renosterveld patches, we assess it as Critically Endangered (CR, B2) under the South African Red list categories and criteria ( Raimondo et al., 2009) and IUCN Standards and Petitions Subcommittee (2017) guidelines.

5.2.2.7.5. Additional specimens examined. South Africa. WESTERN CAPE: 3420 (Bredasdorp): W. flank of S. Spitskop private farm slopes (- BC), 22 March 2017, ♂ & ♀ plants, Zhigila & Muasya 023 ( BOL, K, NBG) ; S. Spitskop, on quartz patches, Renosterveld vegetation (- BC), 23 March 2017, ♂ & ♀ plants, Zhigila & Muasya 024, 026 ( BOL, K, NBG) ; S.W flank slopes of Milanskraal Farm (- BA), 25 March 2019, ♂ & ♀ plants, Zhigila 278 ( BOL, NBG) ; E. flank of N. Spitskop hills, across private farm (- BB), 26 March 2019, ♂ & ♀ plants, Zhigila 287 ( BOL, NBG) .

Figures

Fig. 10. Thesium hirtum: (A) habit based on Esterhuysen (BOL), (B) a twig of female plant, (C) a twig of male plant, (D) lanceolate leaf with raised midrib and scabrid surface, (E) fruits. Photographs: Daniel Zhigila.

Fig. 7. Distribution of species of Thesium section Hagnothesium: (A) T.fragile, (B) T.fruticulosum, (C) T.microcarpum, (D) T.minus, (E).T.hirtum •, T.quartzicolum ▲, (F) T.leptostachyum •, T. longicaule ▲.