Thesium nautimontanum M.A. Garcia , Nickrent & Mucina, 2018

Garcia, Miguel Angel, Nickrent, Daniel L. & Mucina, Ladislav, 2018, Thesium nautimontanum, a new species of Thesiaceae (Santalales) from South Africa, PhytoKeys 109, pp. 41-51 : 44-46

Thesium nautimontanum M.A. Garcia, Nickrent & Mucina sp. nov. Figs 2 , 3

Type.

SOUTH AFRICA. Western Cape Province, Cape Winelands District, Matroosberg, southern slope, 33°23'49.3"S, 19°40'29.5"E, elev. 1016 m; 6 Oct 2007, J. Šibík & I. Šibíková MS463 (holotype: MA-877227).

Diagnosis.

Squamate, glabrous, perennial herb 30-35 cm tall with erect, terete to ribbed sympodial branches; leaves reduced to triangular, acute scales up to 1.7 mm long, increasing in size and density apically, grading into inflorescence bracts. Inflorescences terminal, oblong, crowded spikes bearing up to 50 bracteate flowers, ending in a group of sterile bracts. Flower ca. 2.0 mm long, greenish outside, whitish inside, with triangular external glands between the corolla lobes, internal surface of lobes bearing thick, irregular, spongy and somewhat papillose tissue. Fruit wall marked with conspicuous, strongly raised reticulations.

Description.

Perennial herb, squamate, all parts glabrous; rootstock slender, bearing one or few erect flowering stems 30-35 cm tall with sympodial branching that occurs mostly at the base of inflorescences, branches erect, terete or shallowly ribbed. Leaves all reduced to minute scales, the lower ones 0.5-1.0 × 0.8-1.7 mm, broadly triangular, acute, with darkened tips, erect and more or less appressed to the stem, increasing in size upwards and transitioning into bracts, 1.1-1.9 × 0.8-1.1 mm, ovate-triangular to ovate, acute to acuminate, with entire margins, incurved to naviculate but lacking a marked midrib and bearing in their axils undeveloped buds, progressively more crowded towards the base of the inflorescence, greenish to straw-coloured. Inflorescences terminal (on long and short shoots), oblong, spikes 10.5 × 18.5 mm, bearing (15-)24-50 crowded flowers, ending in a group of about 7-14 sterile bracts. Flowers ca. 2.0 mm long, solitary and sessile in the axil of each bract or with a short (up to 0.8 mm long) pedicel. Flower bracts 1.5-2.2 × 1.0-1.4 mm, similar in shape to the bracts at the base of the inflorescence; bracteoles 2, similar to bracts but smaller. Corolla greenish outside, whitish inside; external glands between the corolla lobes inconspicuous, triangular-ovate, pale orange in colour; hypanthium shallow, 0.2 mm long, internal surface glandular; corolla tube ca. 0.4 mm long; corolla lobes 0.7-0.8 × 0.6-0.7 mm, ovate or ovate-triangular, ± obtuse to slightly hooded and with inflexed tips on fruit, erect, margins entire, lacking hairs inside but with a thick, irregular, fleshy and somewhat papillose tissue. Staminal filaments inserted at junction of hypanthium and corolla tube, very short and inconspicuous, stamen not reaching the corolla lobe sinuses, anthers rounded ca. 0.3 mm in diameter, attached to the corolla tube by a small tuft of hairs. Style very short (ca. 0.1 mm) or lacking, thus stigma sessile, lobes not apparent, reaching the base of the anthers. Placenta twisted, ovules 3. Fruits ca. 3.0 mm long, ovary portion subglobose, 1.5-2.1 × 1.6-2.0 mm, greenish, with slightly marked ribs but reticulations strongly raised, crowned with the 1.0 mm long corolla remnant, pedicel not enlarging into an elaiosome.

Distribution and ecology.

Both collections of this species were made on the Matroosberg Mt. in the Southern Hex River mountain range, Western Cape Province, Cape Winelands District, northwest of the De Doorns settlement.

The holotype collection, from 1016 m elevation, occurred on the southern slopes of the Matroosberg Mt. in the FFs8 South Hex Sandstone Fynbos vegetation according to Rebelo et al. (2006). The soils are acidic lithosols derived from Ordovician sandstone of the Table Mountain Group. This vegetation is, on the type locality, characterised by sclerophyllous, microphyllous fynbos scrub dominated by proteaceous, ericaceous and asteraceous shrubs, with rich graminoid understory containing numerous Cyperaceae and Restionaceae . The area of the South Hex Sandstone Fynbos receives, on average ca. 950 mm of rain annually, peaking from May to August. Summer weather may include heavy mist precipitation at higher altitudes. The mean daily temperatures are 26°C and 2.7°C for February and July, respectively.

The second population was discovered at an elevation of 1920 m, close to the summit of Matroosberg (2249 m). Here Thesium nautimontanum was found in a slight depression supporting a dense restioid-ericoid fynbos wetland (dominated by graminoids of the family Restionaceae and shrubs of Erica L.), surrounded by dry fynbos scrub of the FFs30 Western Altimontane Sandstone Fynbos. The soils here are nutrient-poor and sandy, overlying Table Mountain Sandstone. In contrast to the South Hex Sandstone Fynbos, the altimontane fynbos unit receives higher mean annual rainfall (1380 mm on average), peaking from May to August; frequent fog occurrence (due to summer tradewinds) may carry additional precipitation, mitigating the effect of summer drought at high elevations - a phenomenon common to many Cape Fold Mountains (see Rebelo et al. 2006, p. 69). The mean annual temperature is lower, as it ranges between 22.9°C (February) and 0.1°C (July). The summit regions of Matroosberg regularly receive snow during austral winter.

Phenology.

The specimens examined had spikes containing both flowers and maturing fruits and were thus at similar developmental stages. As the lower elevation collection was flowering in October and the higher elevation one in December, one can extrapolate that the flowering time ranges from ca. September to January.

Etymology.

The specific name stems from the Matroosberg Mt. where the species was first discovered. In Afrikaans, “matroos” means “sailor” and “berg” means mountain. As the Code of Botanical Nomenclature suggests, epithets formed from a geographic name should be in adjectival rather than substantive form, “nauta” (sailor) and “mons” (mountain) become autimontanum.

Conservation status.

According to the World Database of Key Biodiversity Areas (http://www.keybiodiversityareas.org/home), the Hex River Mountains are surrounded by globally and regionally significant areas (UNESCO World Heritage Site 'Cape Floral Region’), but are themselves not currently included. Due to rugged terrain, nutrient-poor soils not viable for large-scale agricultural activities and relative low-key tourism interest (more of importance on the northern flank of the Matroosberg Mt.), the biota of the Hex River Mts. is not under direct, unmitigated threat. However, fynbos scrub is a naturally fire-prone ecosystem, yet too frequent (or too hot) fires might have negative impacts on the natural post-fire regeneration (e.g. Le Maitre and Midgley (1992), Bond and van Wilgen (1996)). The morphology of Pienaar’s collections, having a loose bunch of thin roots, suggests the species is a seeder, hence regenerates after fire from the seed bank.

A section of the Hex River Mts. is under management of CapeNature (the Western Cape provincial nature conservancy authority) and is formally protected in Bokkeriviere Nature Reserve. The coordinates of E. Pienaar M1249 are at 1920 m a.s.l., which place this higher elevation population just south of the boundary of the Reserve. This may well indicate that the species might also occur within the boundaries of the Reserve.

The limited geographic distribution of Thesium nautimontanum is, however, of concern. Using GeoCAT for the two populations, the extent of occurrence was 0.0 and the area of occupancy was estimated at 8.0 km2 which translates to an IUCN Red List category of Critically Endangered, criteria B2 ( IUCN 2014).

Further exploration of these regions should be conducted to determine whether additional populations exist. Even if more populations are encountered, most likely it will stay in the category of Critically Endangered because it is an endemic species restricted to the Matroosberg Mt.

Additional specimens examined.

SOUTH AFRICA. Western Cape Province, Cape Winelands District, Matroosberg, southern slope, 33°23'43.48"S, 19°40'19.46"E, alt. 1920 m, 7 Dec 2007, E. Pienaar M1249 (MA-877228, NBG).

Phylogenetic analyses.

The molecular phylogenetic analyses of the ITS data using the three inference methods (ML, MP and BI) produced results generally comparable to those reported in Nickrent and García (2015), but in addition strongly supported Thesium nautimontanum as sister to the South African and Tropical African clades (Fig. 4 ).

Figures

Figure 2. Thesium nautimontanum M. A. Garcia, Nickrent & Mucina, sp. nov. A habit of plant showing sympodial branching B flowering shoot showing squamate condition, vegetative bracts grading into floral bracts and terminal spicate inflorescence C flower, lateral view D flower longitudinal section E young fruit subtended by bract and two bracteoles. Drawing by J. L. Castillo.

Figure 3. Thesium nautimontanum from the type herbarium specimen. For dimensions, see Figure 2. A spicate inflorescence subtended by bracts B close-up of inflorescence bracts C flower, lateral view, showing triangular external glands in corolla lobe sinuses D flower longitudinal section E ovary longitudinal section showing twisted placental column and ovules (one ovule removed to visualise the placentation) F close-up view of interior surface of corolla lobes showing unusual fleshy tissue on inner surface of corolla lobes G young fruit showing persistent corolla and reticulate outer wall of ovary.

Figure 4. Phylogram for Thesiaceae that includes Thesium nautimontanum sp. nov. (bold). Values at the nodes indicate maximum likelihood bootstrap, maximum parsimony bootstrap and Bayesian posterior probabilities. The scale bar represents number of substitutions per site. Branch lengths are proportional to the amount of substitutional change, except for the branch connecting the outgroup to the ingroup (here shorted for graphical purposes). Group (clade) names are from Nickrent and Garcia (2015). The colour coding for the taxa indicates the general geographic distribution for the species as shown in the inset.