Thesium muasyae Zhigila, 2022

Zhigila, Daniel A. & Muasya, A. Muthama, 2022, Thesium muasyae (Santalaceae), a new species from the limestone fynbos of the Overberg, South Africa, PhytoKeys 201, pp. 1-14 : 1

Thesium muasyae Zhigila sp. nov.

Figs 1 , 2

Type.

South Africa. Western Cape Province, Bredasdorp District, on limestone ridges, south east of Vanderstelskraal Farm, Overberg , 34°24'53.2"S, 20°15'10.5"E [34.41478°S, 20.25292°E]; elev. 60 m; 21 October 2021, D.A. Zhigila & A.M. Muasya 1308 (holotype, BOL; isotypes: K, NBG, PRE) .

Diagnosis.

Thesium muasyae is morphologically similar to T. karooicum Compton (1931). Both species have robust woody habits, well-developed terete to triangular and imbricate leaves, elongated styles, conspicuous external glands between the perianth lobes, persistent perianth segments longer than the fruits, and elaiosomes (Table 1 ). However, T. muasyae differs from T. karooicum in its branching pattern being intricate to sympodial, stems and leaves glabrous, leaves recurved, flowers in lax elongated terminal spikes or racemes in leaf and bract axils, patelliform flowers with post-staminal trichomes attached to the anthers (versus branching pattern divaricate to virgate, stems and leaves minutely scabrous, leaves erect, flowers in terminal capitate head or clusters, urceolate flowers with post-staminal trichomes free from anthers in T. karooicum ). Further the two do not overlap in distribution and ecology, T. muasyae is restricted to the Overberg limestone outcrops whereas T. karooicum is found on the Sandstone Mountains of the Succulent Karoo. Thesium muasyae is also similar to T. sonderianum , but differs in the branching pattern being sympodial to intricate, plant surface glabrous, leaf apex apiculate, inflorescences solitary spikes on branchlets, perianth external glands present, stigma above the anthers, found on limestone slopes (versus dichotomously branched, plant surface minutely pubescent, leaf apex acutely mucronate, inflorescences terminal globose spikes, perianth external glands absent, stigma below the anthers, and restricted to the grasslands in T. sonderianum ). Comparisons of important morphological characters of T. muasyae , T. hispidulum , T. karooicum and T. sonderianum are presented in Table 1 .

Description.

A perennial shrub, arising from woody rootstock, glabrous, to about 30 cm tall. Stems woody, erect to suberect, much branched, 3.0-5.0 mm in diameter, deeply grooved longitudinally. Branches 10-20 in number, mainly from the base, scarcely grooved, angled from> 45° to <90°, branching pattern intricate to sympodial. Leaves terete to triangular, somewhat succulent, adpressed to the branchlets, lanceolate or oblanceolate or somewhat triangular, 1.5-3 × 0.5-1.5 cm, basally decurrent, midrib inconspicuous, not keeled but recurved, margins not distinct or entire, apically apiculate. Inflorescences a lax terminal spike or flowers solitary in leaf and bract axils. Bracts 2-4, leaf-like, slightly adnate to the base of peduncle, linear to lanceolate, 1.0-2.0 × 0.3-0.5 mm, margin entire, apex acute to acuminate, green; bracteoles bract-like, but smaller, adpressed to the pedicel, shorter than flower length. Flowers patelliform, on short peduncles, 5-merous, 2.0-5.5 × 1.5-5.0 mm, perianth lobe segments lanceolate, external gland conspicuously elongated between perianth lobe segments, 2.0-2.5 × 1.0-1.2 mm, lobe apex uncinate, obtuse, incurved, perianth lobe apical trichomes present, lobe margins entire, lobe internal colour white, external colour greenish black; hypanthium clearly marked, to about 0.5 mm long, hypanthium length longer than perianth lobe tube and wider. Stamens equal flower merosity, 0.2-0.3 mm long, staminal filaments exserted slightly above stigmas, attached to the perianth lobe walls by a tuft of trichomes, downwardly-directed basal trichomes absent. Style together with stigma 4-6 mm long; placental column twisted. Fruits subglobose to oblong, ovary portion oval, 5.0-8.0 × 4.5-5.5 mm, green to creamy green, glabrous with 10 conspicuous longitudinal ribs, reticulate veins prominent, pedicels enlarging into elaiosomes, persistent perianth segments equal to longer than the fruit.

Distribution and ecology.

Thesium muasyae was collected on the limestone ridges, south east of Vanderstelskraal Farm, Overberg, Bredasdorp District, Western Cape Province, South Africa (Fig. 3 , triangles) at elevations less than 80 m above sea level. This species occurs on limestone and shale-limestone ecotone scrubs. The limestone soil in the type locality is characterised mainly by calcium carbonate, tiny fossils and other fossilized debris from the coastal limestone of the Bokkerveld Group ( Finch et al. 2014; Penn-Clarke et al. 2018). Physically, the limestone soil is grey to whitish brown.

Phenology.

The collections were made in October with fruits and few flowers. Based on the average of 40 days from flowering to fruiting stage in Thesium species (pers. obs.), we can then extrapolate the flowering period to be between August and November.

Etymology.

The specific epithet ' Thesium muasyae ' honors Professor A. Muthama Muasya for his immense contribution to the floristics and taxonomy of the Overberg and Cape plant species.

Conservation status.

We estimated a total of 10-20 individuals of T. muasyae in a single population over an extent of 0.0 km2 and the area of occupancy of about 5.0 km2. Although this species is on a private farm, grazing from livestock is an immediate threat. In addition, the entire Overberg Renosterveld habitat is considered as Endangered due to intense agricultural activities and the areas being fire-prone ( von Staden 2015; Topp and Loos 2019). These threats together with the GeoCat geographical range estimations translate to the criterion B2, Critically Endangered category of the IUCN (2017) for T. muasyae .

Additional specimens examined.

South Africa. Western Cape Province, Bredasdorp District, on limestone ridge, south east of the Vanderstelskraal Farm , 34°24'52.1"S, 20°15'8.1"E [34.41447°S, 20.25225°E], elev. 63 m, 21 October 2021, D.A Zhigila & A.M Muasya 1312 (BOL!); 34°24'53.2"S, 20°15'10.5"E [34.41478°S, 20.25292°E], elev. 65 m, A.M Muasya & D.A Zhigila 8276 (BOL) .

Figures

Figure 1. Thesium muasyae sp. nov. A twig showing inflorescence arrangements B branchlet showing vegetative arrangements C bract D flower lateral view E flower dissected longitudinally F fruit. Line drawing by Pia M. Eibes.

Figure 2. Morphological features of Thesium muasyae A whole plant in habitat B type material D. A. Zhigila & A. M. Muasya 1308 C branchlet and leaves D fruiting branchlet E fruit lateral view F inflorescences and leaves G flower longitudinal section showing long style in relation to anthers and twisted placental column H flower subtended by bracts I elaiosome on fruit. Photographs by Daniel A. Zhigila. Scale bars: 0.5 mm.

Figure 3. Map of A South Africa with the red outline indicating the Greater Cape Floristic Region (GCFR) B the GCFR showing the type locality (red solid circle) of Thesium muasyae and of the congener species, T. hispidulum (aqua solid stars), T. karooicum (blue solid triangles) and T. sonderianum (fuchsia solid squares).