Thesium hispidifructum N.Lombard & M.M.le Roux, 2023

Lombard, Natasha & Le Roux, M. Marianne, 2023, Thesium hispidifructum (Santalaceae), a New Hispidulous Species from Limpopo, South Africa and Notes on Enigmatic T. celatum, Taxonomy (Clifton, N. J.) 3 (1), pp. 95-108 : 103-105

Thesium hispidifructum N.Lombard & M.M.le Roux , sp. nov. ( Figure 5 )

Type: SOUTH AFRICA. Limpopo Province: Lebowa, Blouberg, Farm Beauly 260 LR , 12 February 1991, L. Smook 7447 (holotype PRE0775984 ) .

Diagnosis: Thesium hispidifructum is morphologically similar to T. disparile in its hairy indumentum, ascending to spreading leaves (4–15 mm long in T. hispidifructum ; 7–11 mm long in T. disparile ), flowers placed in determinate racemose cymes and flower lobes (0.8–1.2 mm long in T. hispidifructum ; ± 0.7–1.2 mm long in T. disparile ) bearded at the inner apex. Thesium hispidifructum is easily distinguished from T. disparile by its tall robust stature (woody stems up to 1 m tall), intricate branching pattern and compact inflorescences with flowers solitary in the bract axils. Comparatively, T. disparile has a short slender stature (herbaceous stems up to 0.15(0.5?) m tall), virgate branching pattern and lax inflorescences with single flowers usually replaced by compound monochasial or dichasial cymes.

Description: Shrub or subshrub, up to 1 m tall, rootstock not known; stems erect, up to 4 mm in diameter, intricately branched above, hispidulous to hispid. Leaves spreading to ascending, sparse below and densely arranged above, often imbricate, linear, 4–15 × 0.3–1.0 mm, hispidulous to hispid. Flowers solitary in bract axils, arranged in 5–10-flowered determinate raceme-like inflorescences; pedicels 0–1.3 mm long. Bracts and bracteoles usually three, leaf-like but smaller, 2–7 mm long, not forming an involucre, bracts fused to at least half of pedicel. Perianth ±campanulate, 2.6–2.7 mm long, elongate receptacle often present, “glands” often visible on outside, exterior hispidulous to hispid; hypanthium 0.3–0.6 mm long; corolla lobes triangular, 0.8–1.2 mm long, apex very slightly cucullate, with dense apical beard of long hairs. Stamens inserted at base of corolla lobes; anthers ± 0.3 mm long. Style 0.2–0.4 mm long, stigma below or reaching the bottom of anthers. Placental column straight; ovules 3. Fruit ± globose, 3.6–4.1 × 1.8–2.3 mm including stipe and persistent perianth, stipe ± 0.4 mm long, persistent perianth 0.9–1.3 mm long, longitudinally and reticulately veined when dry, hispid.

Distribution and habitat: Thesium hispidifructum is endemic to the Limpopo Province in South Africa, where it is known from only four gatherings between Blouberg and Mount Letsjume in the westernmost reaches of the Soutpansberg ( Figure 6 ). Little is known about its habitat. It has been collected among grass in rocky areas as well as in wet wooded areas, on both south facing and northeast facing slopes at elevations between 1675 and 1980 m a.s.l. It is likely restricted to the Soutpansberg Mountain Bushveld [ 21] and Soutpansberg Summit Sourveld [ 21], but field studies are needed to confirm this.

Phenology: Thesium hispidifructum has been collected in flower and fruit in January, February, June, and July.

Etymology: The specific epithet hispidifructum refers to the hispidulous fruit of the species.

Conservation status: Thesium hispidifructum has an extent of occurrence (EOO) of 44 km 2 and an area of occurrence (AOO) of 12 km 2. It is known from only four gatherings at two to three locations in mountainous areas (Blouberg and Mount Letsjume), surrounded by much-transformed low-lying areas (Vivo and surrounds). As the most recent collection/observation of this species was in 1991, the state of these subpopulations is unknown, and needs to be verified during field studies. It is likely that the extensive human settlements and crop development in low-lying areas surroundings these mountains have already resulted in the loss of suitable habitat. Furthermore, expanding anthropogenic influences may easily push this very restricted species to extinction. It therefore qualifies for a threat status of Vulnerable (VU) under Criterion D2 [ 20].

Additional specimens examined: SOUTH AFRICA. Limpopo: Blauwberg , 10 May 1933, A.C. Leeman 110 ( PRE0374089 ); Blauwberg, near trig. beacon , 12 January 1955, L.E. Codd and R.A. Dyer 9063 ( PRE0374090 ); Zoutpansberg, Mt Letsjume, at foot, on S slope , 25 July 1981, F. Venter ( PRE0620517 ) .

Figures

Figure 5. Thesium hispidifructum. (A) Habit. (B) Woody stem. (C) Branches. (D) Hispid branches and leaves. (E,F) Variation in the indumentum from hispidulous to hispid. (G) Compact spike-like inflorescence. (H) Exterior of a rehydrated flower with external “glands” and a hispidulous to hispid indumentum. (I) Cross-section of a rehydrated flower showing the anthers inserted at the base of the lobes and the stigma reaching to the bottom of the anthers. (J) Dry fruit with hispid indumentum. The scale bars represent 1 mm. Photographs taken by N. Lombard (B–J). Images ' South African National Biodiversity Institute. Reproduced with the consent of the South African National Biodiversity Institute (A–C).

Figure 6. Geographical distributions of Thesium hispidifructum (green circles) and three morphologically similar species, T. disparile (blue square), T. rufescens (red triangles), and T. transvaalense (white pentagons).