Thesium ovatifolium N.Lombard & M.M.le Roux, 2019

Lombard, Natasha, Roux, M. Marianne Le & Wyk, Ben-Erik Van, 2019, Thesium ovatifolium (Santalaceae), a new species with ovate leaves from KwaZulu-Natal, South Africa, Phytotaxa 405 (5), pp. 263-268 : 266-267

Thesium ovatifolium N.Lombard & M.M.le Roux , sp. nov. ( Fig. 1 )

Diagnosis:— Thesium ovatifolium is superficially similar to T. goetzeanum and T. racemosum , but differs in its predominantly ovate leaves (linear to narrowly obovate in T. goetzeanum , and linear to linear-lanceolate in T. racemosum ) and bracts (linear-lanceolate in T. goetzeanum and T. racemosum ) with reticulate secondary venation (absent in T. goetzeanum and T. racemosum ), 3- to 4-flowered cymes on inflorescence apices [1(3)-flowered in T. goetzeanum , and 1-flowered in T. racemosum ], and the rosulate arrangement of leaves and bracts in young stems and inflorescences (absent in T. goetzeanum and T. racemosum ). Thesium ovatifolium further differs from T. goetzeanum in its alate (not sulcate) stems, and from T. racemosum in its densely bearded (not papillose) corolla lobes.

Type:— SOUTH AFRICA. KwaZulu-Natal Province: Ngome area, about 60 km east of Vryheid on the R618, 1105 m, 14 October 2018, N. Visser & R. J. Lombard 348 (holotype, PRE; isotypes, NH, NBG) .

Rhizomatous suffrutex, up to 0.3 m tall, vegetative scales present on rhizome and lower parts of aerial stems; stems 5 to 50, arising from rhizome, erect or suberect, virgate, branched in upper half, green, glabrous, alate due to decurrent bases of leaves and bracts. Leaves more or less spreading, lanceolate to ovate, (3.0–)11.0–21.0(–30.0) × 3.0–14.0 mm, glabrous, apex acute or pungent, midrib prominent on both surfaces, secondary veins faintly reticulate, margins entire. Flowers usually solitary in bract axils, sometimes with 2- to 3-flowered cymes, arranged in 6- to 13-flowered determinate racemose inflorescences, terminating in 3- to 4-flowered cymes; pedicels 0–3.0(–5.0) mm long. Bracts lanceolate to ovate, 6.4–16.2(–23.0) × 1.6–5.7(–9) mm, usually acuminate, margins entire, fused to full length of pedicel; bracteoles leaf-like, 4.0–9.7(–15.6) × 0.8–2.3(–3.2) mm. Perianth campanulate, 3.0–5.0 mm long, elongate receptacle often present, “glands” often visible on outside; corolla lobes narrowly triangular, 1.0–1.7 × 0.4–0.6(–0.9) mm, apex slightly cucullate, with dense apical beard. Stamens inserted at base of corolla lobes; filaments 0.3–0.6 mm long; anthers 0.4–0.9 mm long, attached to perianth with post-staminal hairs. Style 0.7–1.4 mm long, stigma ± opposite anthers. Placental column straight; ovules 3. Fruit elliptic, shortly stipitate (stipe ± 0.5 mm long), 5.0– 7.5 mm long including persistent perianth (3.0–5.0 mm long excluding perianth), 2.5–3.5 mm wide, 10-ribbed or occasionally 5- ribbed, smooth or with faint reticulate venation.

Distribution and habitat:— Thesium ovatifolium is endemic to the KwaZulu-Natal Province in South Africa, where it is known from only three localities between Hlobane, and Hlabisa to the south-east ( Fig. 2 ). It is found in grasslands, as well as grassland patches in wooded areas, between 365 and 1178 m a.s.l. The large disparity between the high elevation mistbelt grassland vegetation [Northern Zululand Mistbelt Grasslands (Gs1); Mucina & Rutherford 2006] and the lower elevation wooded grassland vegetation [Northern Zululand Sourveld (SVl22); Mucina & Rutherford 2006] in which this species has been found, is indicative of a widespread distribution.

Phenology and ecology:— Thesium ovatifolium seems to exhibit the typical phenology of South African grassland Thesium species, occurring in the summer rainfall region, flowering and fruiting between September and February. Elaiosomes are often present at the base of the fruits, suggesting myrmecochory as a possible seed dispersal strategy.

Etymology:— The specific epithet ovatifolium refers to the distinctive ovate leaves of this species.

Conservation:— Thesium ovatifolium has an extent of occurrence (EOO) of 103 km 2 and an area of occurrence (AOO) of 12 km 2. It is known from only three localities, of which two are historical records (i.e. number of localities 1– 3). While the population at the type locality near Ngome has been seen by the authors, the two historical localities (near Ngome and Hlabisa) have not been verified. Both localities in the Ngome area are subject to ongoing overgrazing. The locality near Hlabisa was incorporated into the Hluhluwe-iMfolozi Park in 1989, and while it is currently protected, there are signs of historical disturbances, such as overgrazing. The Ngome and Hlabisa localities are ± 75 km apart, and while other populations of T. ovatifolium might be present in between these localities, the area is mostly transformed by rural developments. A preliminary conservation status of Endangered (EN) is therefore suggested under Criterion B1ab(iii) + 2ab(iii) ( IUCN Standards and Petitions Subcommittee 2017).

Additional specimens examined (paratypes): — SOUTH AFRICA. KwaZulu-Natal: Hlabisa, ± 2.7 km [± 4.5 mi] south of Hlabisa , 13 October 1946, J. P.H. Acocks 13068 ( PRE [2 sheets]) ; Louwsburg, about 12 km along road to Vryheid from Ngome Forest Station turnoff, 17 October 1982, B. Schrire 1093 ( NH – image) ; Ngome area, about 60 km east of Vryheid on the R618, 14 October 2018, N. Visser & R. J. Lombard 346 ( PRE), 347 ( PRE), 349 ( PRE) ; Ngotshe District, 57 km east of Vryheid on the R618 between Vaalbank and Nongoma , Farm : Zaagkuil 14333, 15 October 2013, S.P. Bester 11666 ( PRE) .

Figures

FIGURE 1. Thesium ovatifolium. A. Grassland habitat at the type locality near Ngome, KwaZulu-Natal, South Africa. B. Suffrutescent, virgate habit. C. Alate stem. D. Ovate leaf with a prominent midrib and reticulate secondary venation. E. Rosulate arrangement of leaves in a young stem. F. Determinate racemose inflorescence. G. 4-flowered cyme on an inflorescence apex. H. Apical beard on the corolla lobes of a fresh flower. I. Cross-section of a rehydrated flower. J. 10-ribbed fresh fruit with an elaiosome at the base. Scale bar in I = 1 mm. Photographs taken of the holotype, Visser & Lombard 348, by M.M. le Roux (B–D, F–H, J), R.J. Lombard (A, E) and N. Lombard (I).

FIGURE 2. The known geographical distribution of Thesium ovatifolium in the KwaZulu-Natal Province (larger map) of South Africa (insert, darker grey).