Thesium minus (A.W.Hill) J.C.Manning & F.Forest

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 : 300-301

5.2.2.6. Thesium minus (A.W.Hill) J.C.Manning & F.Forest , in Bothalia 43 (2): 215 (2013).

Thesidium minus A.W.Hill in Bull. Misc. Inform. Kew 3: 98 (1915).

Type: South Africa. Western Cape, Caledon Division, Houw Hoek (− 3419), 380 m, without precise date, ♂ and ♀ plants, Schlechter 9431, 380 m (K! Lectotype, designated here; S!, BOL!, PRE!, NBG!, STE! and SAM! Isolectotypes).

Schlechter 9431 is designated as lectotype since both male and female plants are mounted on the same herbarium sheet, the locality is within the typical geographical range of the taxon, and it was cited by Hill (1925) and best fits the protologue.

An erect heath-like annual plant, 5–10 cm tall, yellowish green in general appearance, plant not brittle, stout fibrous rootstock, branches attached mainly to the rhizomes, 4–12 branches; branching pattern virgate, leaves may or may not subtend branchlets. Stems rhizomatous at subterranean and herbaceous at aerial portion, 0.5–1.2 mm in diameter, erect, stems glabrous, prominently sulcate in transverse section. Leaves well developed, upcurved to adpressed to the branchlets, green, glabrous, without a prominent midrib, veins parallel, apex acute, margins entire, concave or convex to straight. In fl orescences in branchlet axils along the main branches, composed of a dichasial (2 or 3 flowered) cyme, shortly pedicellate; bracts and bracteoles leaf-like; bracts fleshy, 2.5–5 × 0.5–1 mm, linear-lanceolate, margins entire, green, acute at tips, longer than the flower, straight; bracteoles bract-like but smaller, 1.5–3 × 0.5–1 mm; flowers campanulate, green, 1–2.5 × 0.5–1.5 mm, 4-merous, perianth lobe external glands absent, perianth lobe segments 0.6–1.4 × 0.5–0.8 mm, lobes ovate to triangular, obtuse or subacute at tips, not distinctly uncinate, somewhat lobulate; lobe tube about 0.4 mm; Male and female plants well differentiated. Male plants: branches more slender than female plants, internodes wider than female plants, 2.5–8 mm; leaves sparse, not imbricate, narrower than in female plants, linear to acicular, 5–10 mm × 0.5–1 mm; inflorescences lax; hypanthium tube quite short to non-existent; stamen tetramerous, staminal filaments exserted at the junction of hypanthium and perianth lobe tubes, about 0.2 mm. Female plants: branches more robust, internodes short, 1.5–2.5 mm; leaves denser than in male counterpart, imbricate, linear, 7.5–13 × 0.4–1 mm; inflorescences a 3-flowered cyme; hypanthium tube length less than the perianth lobe tubes; style short, about 0.2 mm. Fruit a nutlet, ovoid, green, attached to the branch by a swollen pedicel to form a white attenuated elaiosome, 1.5–2.5 × 1–2 mm, conspicuously 10-ribbed and prominent reticulate veins between the longitudinal ribs, capped with green persistent perianth lobe segments, shorter relative to the fruit length ( Fig. 14 ).

5.2.2.6.1. Diagnostic characters. Thesium minus is closely similar to T. fruticulosum in their glabrous plant surfaces, multi-stemmed basal parts, terete stems, fastigiate branching pattern, leaves without a conspicuous midrib, bracts and bracteoles leaf-like and flowers attached to the branchlet by a short to non-existent pedicel. T. minus differs from T. fruticulosum in being annual, with a fibrous rootstock and a rhizome present, 5–10 cm in height, (versus perennial suffrutex, simple tap root system, to about 30 cm), leaves in male plants more slender (leaves similar in both male and female plants), internodes wider, 2.5–8 mm wide (versus internodes shorter in both male and female plants, 0.2–2 mm), fruit elaiosomes absent, rarely present (versus fruit elaiosomes present).

5.2.2.6.2. Distribution and habitat. Thesium minus occurs in fynbos on mountains of the Caledon, Bredasdorp and Riversdale divisions of the Western Cape Province and as far east as to Grahamstown in the Eastern Cape Province ( Fig. 7D ). It is usually found in open vegetation on sandstones or quartzite soils from 300 to c. 700 m a.s.l.

5.2.2.6.3. Conservation status. von Staden (2015) assessed T. minus as a data deficient taxon and considered it taxonomically problematic. The species was under studied and can easily be confused as T. fruticulosum . In our assessment, T. minus is rare in its major habitats and may be found in protected reserves only. We therefore evaluated the species as a Rare species under the IUCN Standards and Petitions Subcommittee (2017) guidelines.

5.2.2.6.4. Additional specimens studied. South Africa. EASTERN CAPE: 3325 (Port Elizabeth): Port Elizabeth (- CB), 11 Oct 1931, ♂ & ♀ plants , Holland 3690 ( BOL) ; Regio occidentalis , in montibus prope Vogelgat (- BA), 15 Jan 1961, ♂ & ♀ plants, Esterhuysen 5214 ( HBG, BOL) . 3326 (Albany): Grahamstown Nature Reserve (- AD), 20 Sep 1963, ♀ plants, Staufer 5180 ( BOL) ; Grahamstown Nature Reserve (- AD), 02 Dec 1977, Hillard 10829 ( NBG) .

WESTERN CAPE: 3319 (Worcester): North stop, between Michell Park and Delville, Worcester (− AD) , 16 Jan 1961, ♂ & ♀ plants, Esterhuysen 28741 ( BOL) . 3323 (Willowmore): West of Joubertina (- DD) , 17 Nov 1958, ♀ plants, Acocks 20025 ( PRE) . 3418 (Simonstown): Harold Porter Botanic Garden (- BD) , 14 Jan 1976, ♂ plant, Brenan 14051, ♀ plant, Brenan 14, 050 ( NBG) ; Lake Pleasant hotel, Knysna Division (- DD) , 06 Aug 1960, Acocks 21308 ( PRE) . Mountains East of Steenbras River (- BC) , 02 Jan 1921, Marloth 10, 074 ( PRE) . 3419 (Caledon): Houw Hoek (- AA) , 26 Nov 1898, ♂ & ♀ plants, Schlechter 9432 ( PRE) ; Houw Hoek, in montibus (in mountains), 26 Nov 1897, Schlechter 9431 ( PH, BOL) ; Vogelgat, above Dragonfly Pool (- AD) , 08 Apr 1987, ♂ & ♀ plants, Williams 3795 ( NBG) , Collibus (hills), Riet Fontein, Elim (- AB) , 09 Dec 1896, Bolus 8601 ( K, BOL) ; Houw Hoek, railway line (- AB) , 29 Sep 1970, Esterhuysen 32490a ( BOL) ; Vogelgat, above Dragonfly Pool (- AD) , 8 Apr 1987, ♂ plant, Williams 3794 ( NBG) .

Figures

Fig. 14. Thesium quartzicolum: (A) habit and substrate of female plants, (B) habit and quartz-silcrete substrate of male plants, (C) an amplified view of female plants displaying fruiting jointed branchlets, (D) a shoot showing scale-like bracts and bracteoles subtending fruits, (E) a male shoot displaying 4-merous flower and stamen, (F) female flowering twig, (G) detailed floral parts in relation to scally leaf, cartilaginous bract and bracteole margins, (H) longitudinal section of floral parts.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 ▲.