Tiganophyton karasense Swanepoel, F.Forest & A.E.van Wyk, 2020

SWANEPOEL, WESSEL, CHASE, MARK W., CHRISTENHUSZ, MAARTEN J. M., MAURIN, OLIVIER, FOREST, FÉLIX & VAN WYK, ABRAHAM E., 2020, From the frying pan: an unusual dwarf shrub from Namibia turns out to be a new brassicalean family, Phytotaxa 439 (3), pp. 171-185 : 180-182

Tiganophyton karasense Swanepoel, F.Forest & A.E.van Wyk , sp. nov.

( Figs. 2 & 3 )

Type:— NAMIBIA. Karas Region: Groot Pan, 38 km northeast of Tses along road, on edge of pan , 2518CB , 1030 m, 19 December 2010, Swanepoel 365 (holotype WIND; isotypes PRE, PRU) .

Evergreen, dwarf shrub, 0.3–0.8 m tall and of nearly equal diam., branching from just below or above ground level, re-branching towards apex; long shoots (dolichoblasts) slender, erect or arcuate-ascending, round, often sulcate, up to 18 mm diam., with long soft hairs, glabrous on older stems, with many short shoots (brachyblasts) in axils of leaves, 3–10 mm long, completely covering shoot, leaves on older short shoots sometimes withering, exposing persistent core as a short thorn/protuberance, often blunt, sometimes only scars remaining; bark stramineous, on older stems ashy with black spots, smooth or longitudinally fissured and peeling. Leaves simple, sessile, dimorphic depending on whether on long or short shoots, pale green, often turning yellowish or orange with age, eventually drying to stramineous; on long shoots usually closely spirally arranged, lamina trullate or deltoid, incurved, thickened towards base, bluntly keeled abaxially, flat adaxially, apex acute to attenuate, margin irregularly fimbriate, keel sometimes sparingly fimbriate, ca. 1.2–1.9 × 0.6–0.9 mm; on short shoots spirally arranged, tightly packed in rosettes 2–3 mm diam., 3–10 mm long, lamina ovate, obovate, narrowly obovate or trullate, flat adaxially, slightly incurved especially towards apex, bluntly keeled abaxially, thickened towards acute apex, minutely apiculate, margin often somewhat membranous, fimbriate (less so or fimbrillae lacking on leaves towards base of shoot), 0.8–1.6 × 0.6–1.0 mm, increasing in size towards apex. Inflorescences simple, flowers borne only on short shoot in axils of bracts. Bracts narrowly obovate, oblong-elliptic or subspathulate, concave adaxially, slightly larger than surrounding leaves, otherwise similar. Flowers borne singly, 1–4 per rosette (short shoot) in axil of bracts, laterally compressed, sessile, hypogynous. Calyx tubular, 4-lobed, thin, papery, pale yellow, 1.7–2.1 mm long, lobes 0.8–1.2 × 0.5–0.6 mm, lobes narrowly triangular or narrowly ovate, joined across sinuses between lobes with a thin, membranous tissue (like a “pleat” if viewed from outside), the latter “membrane” with long shaggy hairs on inside towards apex, outside glabrous or sparsely hairy, pale yellow. Disk (receptacle?) 4- lobed. Corolla of 4 petals, free, ± falcate or oblong, prominently longitudinally ridged (“midrib”), sessile, apex obtuse or emarginate, pale white, 2.0–2.3 × 0.5 mm, margins entire or minutely ciliate towards apex. Stamens antesepalous, free, ± equal, spreading, exserted (± 1.6 mm); filaments filiform, slightly flattened, membranous when dry, ± 3.8 mm long, 0.1 mm diam., pale green, inserted on apex of disk lobes with articulation visible, alternating with petals; anthers dorsifixed, introrse, 0.5 mm long; pollen prolate, tricolporate, surface faintly reticulate, lime-yellow. Ovary deeply bilobed, ca. 0.4 mm diam., each lobe with 2 basally attached ovoid ovules, 0.3 × 0.2 mm, glabrous; gynophore slender, 0.7–1.0 mm long, often seemingly (due to lateral flattening of flower) eccentrically inserted on disk, initially erect in young developing flowers, becoming bent in near S-shape following anthesis, resulting in ovary orientated horizontally or occasionally inverted; style ca. 1.8 mm long, elongating to ca. 2.8 mm, tapering from ca. 0.2 mm to 0.1 mm diam., inserted between lobes (gynobasic), stigma capitate, when viewed from above circular, elliptic, trigonous or tetragonal. Fruit 1-seeded, hard, provisionally interpreted as a nutlet (see Discussion), borne in original position of flower within compressed remains of calyx and corolla, 2.1 × 1.6 × 0.8 mm; nutlet globose, ellipsoid or ovoid, slightly compressed, 0.8–1.0 mm diam., smooth, pale yellow-brown.

Phenology:— Flowering during summer (December and January), following good rainfall. The dry fruits (nutlets) are retained amongst the compact leaves and bracts of short shoots, apparently for several seasons.

Distribution and habitat:— At present only known from three localities in arid southeastern Namibia ( Figs. 4 & 5 ), where it is strictly confined to three seasonal pans: Groot Pan, Kleinvaalgras Pan, and a pan on the farm Middelplaas, all within a radius of 35 km. It is rare, although locally common with less than 1000 plants known. Tiganophyton karasense grows on recent calcareous substrate in these pans that are underlaid by shales and mudstones of the Prince Albert Formation of the Ecca Group of the Karoo Supergroup. The calcareous nature of the substrate probably has its origin from runoff of the nearby southwestern escarpment of the Weissrand Plateau ( Miller & Schalk 1980). Geomorphologically the Weissrand Plateau ( Fig. 5 ) is an area covered by calcrete deposits (calcium carbonaterich duricrusts) and pockmarked by solution hollows (dayas) associated with aligned drainage channels and old dunes sandwiched between the Nama-Karoo Basin and dune fields of the Kalahari sandveld ( Goudie & Viles 2015). Several large, seasonal, endorheic pans are associated with drainage on the Weisrand Plateau itself and especially from its southwestern edge, and these should be explored for possible further populations of the new species ( Fig. 5 ). Plants occur in Karas Dwarf Shrubland, part of the Nama-Karoo Biome, at elevations of 1020–1030 m.Average annual rainfall in the region is 100–150 mm, falling predominantly in summer and autumn, but highly variable and unpredictable ( Mendelsohn et al. 2002).

The plants were noticed on the edges as well as in the pans, occasionally in shallow water for a couple of weeks following a good rainy season. The species may eventually prove to be more widespread in the area, as what appears to be suitable habitat is not limited to the specific localities where it was found. However, it is absent from several pans in the area with seemingly suitable habitat, but with different underlying geology. Lower rainfall and higher temperatures may have a negative effect on the species since it seems to be more dependent on moisture than the matrix vegetation surrounding the pans and hence its specific habitat requirements. The known range falls within the zone in Namibia with the highest average maximum temperatures during the hottest month (36° C in January/February; Mendelsohn et al. 2002).

Conservation status:— Tiganophyton karasense is rare and localized with only three locations known. It should be considered as Vulnerable (VU D1) due to its small population size, the latter estimated to number fewer than 1000 mature individuals ( IUCN 2012).

Etymology:— Tiganophyton is derived from the Greek τηγάνι, tigani, a frying pan, referring to the habitat of this species, which can be extremely hot, and φυτών, fyton, a plant. The specific epithet “ karasense ” denotes the Karas Region in southern Namibia, where all known localities of the new species are located.

Notes:— The new species has long shoots and short shoots, each with a different type of foliage leaf ( Figs. 2B & C , 3D & E ). Long shoots develop first, followed by short shoots in the leaf axils. Once the short shoots are well developed, the long shoots lose their leaves. Older long shoots are densely covered by short shoots, the latter appearing as rosettes of tightly packet scale-like leaves and bracts. Flowers are borne on short shoots only ( Figs. 2D , 3B ) after a rosette has reached a diameter of 2–3 mm. Short shoots seem to continue to grow incrementally for several seasons, and their leaves and bracts are persistent; “annual” whorls of new growth are evident apically. New long shoots develop from the apex of some short shoots ( Figs. 2C , 3C ), the latter evidently retaining the ability to become long shoots. Nutlets (“seeds”) are not actively released from the plants, but remain in their original position hidden amongst the densely packed leaves of the short shoot rosettes. They are probably released only after a plant has died or when a rosette has withered, a process that may take several years under the arid conditions of this habitat.

Additional collections examined (paratypes):— NAMIBIA. Karas Region: Groot Pan, 38 km northeast of Tses along road, near centre of pan , 2518CB , 1030 m, 28 January 2010, Swanepoel 364 ( WIND); Kleinvaalgras Pan, Kleinvaalgras , edge of pan, 2618BA , 1026 m, 12 March 2011, Swanepoel 367 ( WIND); Keetmanshoop, Middelplaas, pan along main road before entrance , 2618BB , 12 February 1998, Strohbach 3636 ( PRE!, WIND!); Middelplaas, along road on edge of pan , 2618BB , 1023 m, 9 January 2011, Swanepoel 366 ( WIND) .

Figures

FIGURE 2. Tiganophyton karasense. A. Plant habit and habitat. B. Part of an old long shoot showing short shoots with their rosettes of foliage leaves (mainly) and bracts. C. Young, actively elongating long shoots with short shoots not yet fully developed in leaf axils; arrows indicate where a long shoot emerges from the apex of a short shoot. D. Long shoot densely covered with short shoots, the latter bearing flowers. Photographs: W. Swanepoel.

FIGURE 3. Tiganophyton karasense. A. Branchlet with short and long shoots; parts of oldest stem with scars left by withered short shoots. B. Short shoot with three flowers. C. Long shoot developing from apex of a short shoot. D. Long shoot leaves; dorsal view left, ventral view right. E. Short shoot leaves; dorsal view left, ventral view right. F. Semi-stylized depiction of a flower (in reality floral parts closely packed with gynophore tightly appressed to ovary), with calyx, two front stamens and a front petal removed. Note gynophore bent in near S-shape, horizontal orientated bilobed ovary, and gynobasic style (portion of style between ovary lobes indicated with stippling; ovary lobes opaque). G. Flower (side view). H. Calyx viewed from outside. I. Calyx opened out and viewed from inside. J. Nutlet. K. Flattened remains of flower with nutlet enclosed in the persistent calyx. Scale bar = 10 mm (A), or 1 mm (B–K). A, C, J & K from Swanepoel 364 and B & C–I from Swanepoel 365. Artist: Daleen Roodt.

FIGURE 4. Topographical map showing the known distribution (black dots) of Tiganophyton karasense in southeastern Namibia. The insert shows a map of southern Africa with names of countries; the grey rectangle indicates the area depicted by the topographical map.

FIGURE 5. Landsat image on which is shown the village of Tses in Namibia and the three seasonal pans (coloured green) from where Tiganophyton karasense is known at present: A = Groot Pan; B = Kleinvaalgras Pan; C = Pan at Middelplaas. These pans receive their drainage from the calcrete-covered Weissrand Plateau, the extensive palely coloured area dotted with darkly coloured depressions (dayas). Linear aeolian dunes of the Kalahari (KD) are visible in the upper right-hand corner of the image and believed to have covered the now exposed Weissrand Plateau in the distant past. Image: NASA, based on a tri-decadal global Landsat 7 orthorectified ETM+ Pan-sharpened image.