Petalidium konkiepense Swanepoel & A.E.van Wyk, 2023

Swanepoel, Wessel & Van Wyk, Abraham E., 2023, Petalidium konkiepense (Acanthaceae), a new species from Namibia, Phytotaxa 585 (1), pp. 29-38 : 30-37

Petalidium konkiepense Swanepoel & A.E.van Wyk , sp. nov. ( Figs 1 & 2 )

Diagnosis: —A woody dwarf shrub up to 1 m tall, morphologically most similar to Petalidium linifolium , differing by having the leaf lamina oblanceolate or rarely a few narrowly lanceolate (sensu Lindley), flat, subconduplicate to conduplicate towards the apex (vs. linear or narrowly lanceolate [sensu Lindley], flat, often recurved towards the apex), pale green or yellow-green and not glossy (vs. pale to bright green and glossy, covered with a glutinous secretion), with midrib and 1–4 principal lateral veins each side (vs. principal lateral veins absent), venation prominent both sides (vs. adaxially only), indumentum puberulent, abaxially often with widely spaced short-stalked glandular and robust long-stalked multi-cellular glandular trichomes in addition (vs. glabrous, except for short conical trichomes adaxially).

Type: — NAMIBIA.|| Kharas Region : Bethanien District , Farm Soutkuil 181. Along track to Farm Wegdraai 179, ca. 1 km from northernmost farmstead, 2717 AD, 806 m, 26 August 2022 , Swanepoel 613 (holotype WIND!; isotypes PRE!, PRU!) .

Woody, dwarf shrub up to 1 m tall. Stems multi-stemmed from just below or above ground level from thick rootstock or main stem, up to 150 mm in diam., bark rough and fissured, grey or dark brownish grey; older distal stems rigid, cylindrical, bark smooth or longitudinally fissured, cream or white; young stems quadrangular, green, becoming white with age, puberulent, usually with widely spaced, long, robust, multi-cellular glandular or eglandular trichomes, glabrescent, cystoliths visible. Leaves opposite and decussate on new shoots, fascicled on older stems, subsessile; lamina oblanceolate, rarely few narrowly lanceolate (sensu Lindley), flat, often subconduplicate to conduplicate towards apex, often appearing linear (when dry margin strongly involute towards midrib), up to 24.0 × 4.4 mm, pale green, semi-succulent, puberulent, usually with widely spaced short-stalked glandular and robust long-stalked multicellular glandular trichomes on margins and abaxially on venation, apex acute, margin entire, slightly incrassate, midrib and 1–4 principal lateral veins conspicuous, pale green or pale yellow, prominently raised on both surfaces, cystoliths visible on both surfaces, often conspicuous on veins and margins. Flowers solitary, axillary; bracts absent; pedicels (below bracteoles) 3–6 mm long; bracteoles ovate, symmetrical, membranaceous, 15–21 × 9–12 mm, apex attenuate, apiculate, base sub-cordate, cordate, rounded or truncate, white or cream, often violet, indigo or brown in places, venation reticulate, prominent both sides, conspicuous, green, dark green, brown, violet or indigo, puberulent abaxially, with scattered short-stalked glandular trichomes in addition, midrib rectilinear, main veins and margins with widely spaced, robust, long-stalked, multi-cellular glandular and eglandular trichomes up to 4.5 mm long, adaxially glabrous to sparsely puberulent with short-stalked glandular trichomes in places, margins sparsely lanate, cystoliths linear or linear-oblanceolate, visible on midrib and lateral veins, often conspicuous. Calyx 6.1–10.9 mm long including basal tube of 1.6–3.3 mm long, lobes 5, regular, lanceolate, acute, unequal, 2.9–7.0 × 1.2–1.7 mm; puberulous abaxially and with scattered multi-cellular stalked glandular trichomes of various lengths, strigose adaxially with short-stalked glandular trichomes in addition, margins ciliate. Corolla with narrow unexpanded portion of tube cylindrical, slightly narrowing towards expanded part, laterally slightly flattened, 26–37 mm long with lobes straightened, narrow portion 8.0– 11.8 mm long, 1.9–3.6 mm diam., expanded portion 10.0– 11.8 mm long, distal part of narrow portion and expanded portion puberulous outside with scattered short-stalked glandular trichomes in addition, inside of anticous portion towards mouth with few long stiff white hairs, throat puberulous, inside otherwise glabrous; lobes patent, obovate, apices rounded, often retuse or truncate, margins entire, upper lobes free for 80–90%, overlapping, 10.0–11.1 × 7.5–12.5 mm, lateral lobes 10.0–13.1 × 7.0– 13.1 mm, front lobe 10.0–12.6 × 8.0– 13.7 mm, lobes violet (heliotrope), mauve or blue, front lobe with two narrowly triangular nectar guides, the latter pale yellow, indigo or inconspicuous, sometimes prominent, lateral lobes with two narrowly triangular indigo markings towards base; palate chestnut towards base of expanded portion, slightly prominently transversely 6–8-ribbed. Stamens didynamous, inserted dorsally in throat, free parts of filaments fused for 1.4–2.0 mm at base, fused part prominent, adnate to tube, free parts tapering towards apex, flattened, sparingly puberulous with few short-stalked glandular trichomes, longer filament 6.3–8.0 mm long, shorter filament 4.4–5.0 mm long, outer filament trace decurrent to base of tube, puberulous; filament curtain phaulopsoid ( Manktelow 2000); anthers 2-thecous, thecae oblong, equal, 3.0– 3.5 mm long with scattered short-stalked glandular trichomes, apex obtuse, base with short lobes (sagittate). Gynoecium ca. 23 mm long; ovary ovoid, laterally compressed, 2.0 × 1.0– 1.3 mm, inserted on fleshy disc, towards apex with scattered short-stalked glandular trichomes; style filiform, 14–19 mm long, puberulous with in addition very short-stalked glandular trichomes, stigma lobes linear, unequal, longer lobe 1.0– 1.6 mm long, shorter lobe ca. 0.5–1.2 mm long. Capsule elliptic, 6.5–7.0 × 3.4–5.0 mm long, tawny, glossy, glabrous; seeds not seen.

Phenology: —Flowers and fruit have been recorded from June to September.

Distribution and habitat: —At present, Petalidium konkiepense is only known from the area between the lower Fish and Konkiep rivers. All known populations fall within the drainage area of the Konkiep River on the farms Churutabis-Sonntagsbrunn 108, Soutkuil 181, and Bobbejaankrans 180 in southern Namibia ( Fig. 3 ). It occurs in the Northwest Canyon Lands Landscape unit of Burke (2017) on arid hillsides and along drainage lines at elevations of 780–900 m a.s.l., ca. 155 km inland from the Atlantic Ocean. Plants grow in shallow clayey soil among limestone or shale rocks ( Fig. 1 ) of the sedimentary Nama Group ( Mendelsohn et al. 2002). Average annual rainfall in the area is less than 50 mm and falls mainly in summer ( Mendelsohn et al. 2002).

Conservation status: — Petalidium konkiepense is known from only one location with four small sub-populations where it is locally common. Although a brief search at various other localities with seemingly suitable habitat did not reveal any plants, it is probably more widespread than currently known. Petalidium konkiepense is here considered to be in immediate conservation danger due to its restricted distribution. Although protected in the Canyon Nature Park, prolonged droughts and rising temperatures seem to have a negative effect on the species, since in all the subpopulations most plants show signs of die-back and are in poor condition with many dead branches. Admittedly, some plants manage episodic drought by dying back and resprouting, so this is not necessarily an indication that plants are in immediate danger of dying. Hence monitoring of the plants over a longer period of time is recommended to establish the permanence of the observed die-back. Given the small extent of occurrence (EOO) of 119 km ², the single location, and the observed die-back on most of the mature individuals, a conservation status of Endangered EN B1ab(v) is proposed (IUCN 2012).

Etymology:— The specific epithet refers to the Konkiep River (a tributary of the Fish River) in the Gariep Centre of Plant Endemism in southern Namibia. The name “Konkiep” (also spelled “Koin kieb”, “Konkip”, or “Koanquip”) is derived from the Khoesaan language Khoekhoegowab ( Alexander 1838, Sprigade & Moisel 1904, Nienaber & Raper 1983, Raper et al. 2014). Its meaning, however, is uncertain and has most probably been lost in time. It has been claimed by some authorities that “Konkiep” is an adaptation of “Goageb” (also spelled “Goangib”), which is said to mean “the swollen twin river” ( Nienaber & Raper 1983, Raper et al. 2014). However, we do not find this explanation convincing as, according to probably the earliest report on the geography of the region by Alexander (1838), Goageb (as “Gnuanuip”), is the name of a tributary of the Konkiep (as “Koanquip”) River.

Notes: —In addition to P. linifolium ( Fig. 4 ), the new species can also be confused with P. cymbiforme ( Fig. 5 ), a species with relatively narrow leaves and a more or less similar distribution range ( Fig. 3 ). However, the leaves of P. konkiepense are oblanceolate, rarely lanceolate (sensu Lindley) with principal lateral veins (vs. linear, rarely lanceolate [sensu Lindley], with lateral veins absent), the bracteoles are membranaceous, white or cream in colour (vs. cartilaginous, green, or pale green), and the colour of the corolla of P. konkiepense is violet (“heliotrope”), mauve or blue (vs. white or cream). Some of the morphological features to distinguish among P. konkiepense , P. linifolium , and P. cymbiforme are provided in Table 1 . Also see Figs 4 & 5 .

All the mentioned species are from the infrageneric group composed of plants with regular, five-parted calyces (Obermeijer 1936, Tripp et al. 2017).

Additional specimens examined (paratypes): — NAMIBIA, || Kharas Region: Farm Churutabis-Sonntagsbrunn 108, at entrance gate to Fish River Lodge, 2717AD, 784 m, 27 August 2022, Swanepoel 615 ( WIND!); On Soutkuil , 2717CB, 30 June 1986, Craven 2512 ( WIND!); Farm Bobbejaankranz [Bobbejaankrans], on road from Soutkuil to house, 2717CB, 22 September 1989, Craven 3493 ( WIND!); Bethanien District, Farm Soutkuil No. 181, 2717CB, no date, Owen-Smith 1203 ( WIND!); Farm Soutkuil 181, track between Soutkuil and Farm Wegdraai 179, 5.7 km from northernmost farmstead on Soutkuil , 2717CB, 894 m, 26 August 2022, Swanepoel 614 ( WIND); Farm Soutkuil 181, 2717CD, 14 July 1988, Craven 3332 ( WIND!); Farm Soutkuil 181, approaching Soutkuil house from southern side, 2717CD, 1 July 1991, Craven 3936 ( WIND!).

Figures

FIGURE 1.Petalidium konkiepense, habitat andhabit.A. Plant inflower (right foreground) withseveral plants (low greyish dwarf shrubs— one marked with an asterisk—in background), growing among limestone rocks of the Nama Group (Farm Churutabis-Sonntagsbrunn 108, ||Kharas Region, Namibia). B. Mature plant, mainly past flowering, with persistent bracteoles (Farm Soutkuil 181, ||Kharas Region, Namibia). Photographs by W. Swanepoel.

FIGURE 2. Petalidium konkiepense, morphology of flowers and leaves. A. Branchlet showing narrow leaves and violet flower. B. Flower in front view; mauve variation. C. Flower in side view, with bracteoles; mauve variation. D. Leafy shoot with flower in front view, and with bracteoles; violet variation. E. Leafy shoot with flower in lateral view, and with bracteoles; violet variation. Photographs by W. Swanepoel.

FIGURE 3. Known distribution of Petalidium konkiepense (black dots; ●) based on specimens in Herb WIND. Also depicted are the distribution ranges of P. linifolium (A. green) and P. cymbiforme (B. orange).

FIGURE 4. Petalidium linifolium, flower and leaf morphology. A. Branchlet with relatively short linear leaves, flower and bracteoles. B. Branchlet with relatively long linear leaves, flower and bracteoles. C. Flower and bracteoles in lateral view. D. Flower in front view. Photographs by W. Swanepoel.

FIGURE 5. Petalidium cymbiforme, flower and leaf morphology. A. Branchlet with flowers and linear leaves. B. Shoot showing flowers and bracteoles. C. Flower in front view, with bracteoles. D. Flower in lateral view. Photographs by W. Swanepoel.