[Botany • 2025] Petalidium engoense (Acanthaceae) • A New Species from Angola and Namibia, with notes on phenotypic plasticity in the genus

 

Petalidium engoense

in Swanepoel, Becker Van Wyk, 2025. 

 DOI: doi.org/10.11646/phytotaxa.734.1.2

Abstract 

Petalidium engoense, first collected in May 2025, is here described as a new species. It is a range-restricted species, only known from the western edge of the escarpment zone (Great Escarpment of southern Africa), in the hilly area bordering the Engo Valley (northwestern Namibia), and to the north of Espinheira (southwestern Angola), in the Kaokoveld Centre of Endemism. It grows amongst boulders on arid hillsides, and along an ephemeral riverbed. Diagnostic characters for P. engoense include the pale greyish green appearance of the plants, ashy-grey to white fissured bark on older stems, vegetative parts with a dense white indumentum of very small stellate (stellulate) and dendritic trichomes appearing tomentose, semi-succulent leaves, burgundy flowers borne in short few-flowered dichasia with inflorescence axis becoming spiny with age, and narrowly ovate, attenuate to acute, prominently reticulate bracteoles. The flowers of P. engoense are distinctive in having all lobes coloured burgundy, and the anterior lobe with two yellow ensiform nectar guides. A comparison of key morphological features distinguishing P. engoense from P. namibense, its closest relative in appearance, is provided. Based on IUCN Red List criteria, a provisional conservation assessment of Critically Endangered (CR) is recommended for the new species. The paper also summarises current knowledge of phenotypic plasticity within Petalidium in response to environmental variation. This contribution forms part of ongoing taxonomic studies on the genus.

endemism, Engo River, Engo Valley, flora, Hartmann Valley, Iona National Park, Kaokoveld Centre of Endemism, Kunene Region, Namib Desert, Namibe Province, Ruellieae, taxonomy, variation, Eudicots

Petalidium engoense. Habit, vegetative and reproductive features.   
A. Woody stem with fissured bark at the base of a mature plant. B. Flowering shoot with semi-succulent leaves, which are covered in matted, greyish white indumentum and typically ca. folded upward along the midrib for their full length. C. Portion of a plant showing an open flower along with several old inflorescences; the inflorescence axes usually persist and have become spiny with age.

Photographs by W. Swanepoel.

Petalidium engoense. Morphology of inflorescences and flowers.
A. Distal part of a shoot showing both an open flower and a faded, brownish one, along with several bracteoles. B. Old inflorescences with dried, shriveled bracteoles and persistent axes that have become spiny (indicated by arrows). C, E. Frontal view of a flower showing uniformly coloured corolla lobes; the anterior lobe with two yellow, ensiform nectar guides. Visiting ants were feeding on scale insect larvae. D, G. Flower and bracteoles in lateral view. F. Flower with bracteoles, viewed from above. Photographs by W. Swanepoel.

Petalidium engoense. Habitat and habit.
A. Several plants growing among rocks along a seasonal drainage line in the Engo Valley, Kunene Region, Namibia. B. A mature plant (ca. 800 mm tall) displaying a densely branched structure with greyish green foliage. Photographs by W. Swanepoel.

Wessel SWANEPOEL, Rolf W. BECKER and Abraham E. VAN WYK. 2025. Petalidium engoense (Acanthaceae), A New Species from Angola and Namibia, with notes on phenotypic plasticity in the genus.  Phytotaxa. 734(1); 9-19. DOI: doi.org/10.11646/phytotaxa.734.1.2 [2025-12-16]

 

[Botany • 2025] Petalidium sebrabergense (Acanthaceae) • A New Species from Namibia

  

Petalidium sebrabergense  Swanepoel & A.E.van Wyk,

in Swanepoel et van Wyk, 2025. 

 DOI: doi.org/10.11646/phytotaxa.728.1.2

Photographs by W. Swanepoel.

Abstract

Petalidium sebrabergense, first collected in May 2024 and easily mistaken for P. cirrhiferum, is described here as a new species. It is a range-restricted species, only known from Namibia’s Zebra Mountains, within the Kaokoveld Centre of Endemism. It typically grows on plains, hillsides, and along ephemeral riverbeds and drainage lines, primarily in soils derived from anorthosite and gabbro of the Kunene Igneous Complex. Key distinguishing features for P. sebrabergense include the pale green appearance of the plants, vegetative parts with indumentum of dense, simple, multi-cellular stalked glandular trichomes, frequently interspersed with widely spaced eglandular simple and bifurcate trichomes, often with some leaves additionally bearing sparsely branched dendritic trichomes. The flowers are borne in racemose dichasia and are notable for having the corolla lobes lilac or mauve, with both sides concolorous. A comparison of key morphological features distinguishing P. sebrabergense from P. cirrhiferum, its closest look-alike, is provided. Brief comparisons are also made with P. huillense, P. subcrispum, and P. welwitschii, species with which it can be confused, particularly in herbarium specimens. Based on IUCN Red List criteria, a provisional conservation status of Critically Endangered (CR) is recommended for the new species.

anorthosite, endemism, Epupa, flora, Kaokoveld Centre of Endemism, Kunene Igneous Complex, Kunene Region, Kunene River, Ruellieae, Swartbooisdrif, taxonomy, ultramafic rocks, Zebra Mountains, Eudicots

Petalidium sebrabergense. 

Habit and leaf variation. 

A. Dwarf shrub ca. 400 mm high with relatively narrow leaves, growing among dark rocks of leucotroctolite. B. Dwarf shrub ca. 250 mm high with relatively broad leaves, growing in whitish anorthosite-derived soil.  

Habitat and habit. 

A. Dwarf shrubs in foreground with bright green foliage following recent rains; in open shrub and tree savanna of inter-mountain valley on whitish soil derived from anorthosite. B. Spreading dwarf shrubs in an ephemeral stream bed on whitish anorthosite-derived soil. 

Photographs by W. Swanepoel.

Petalidium sebrabergense. Morphology of flowers.
A. Shoot with relatively narrow leaves and flowers. B, C, D, E. Flowers in front view, each from a different plant to show variation. Corolla lobes are lilac or mauve (pale violet), both surfaces concolorous. F, G. Flower in side view; bracteoles abaxially with numerous simple multi-cellular stalked glandular trichomes up to 2 mm long (not or barely visible to the naked eye), but lacking dendritic trichomes.

Photographs by W. Swanepoel.

Petalidium sebrabergense Swanepoel & A.E.van Wyk, sp. nov. 

 Diagnosis:—A woody dwarf shrub up to 0.75 m tall, morphologically most similar to Petalidium cirrhiferum, differing by lacking dendritic trichomes on stems (vs. dendritic trichomes present); indumentum on leaves with trichomes sparsely to densely scattered (vs. appearing matted or floccose); leaf lamina lanceolate (sensu Lindley’s definition [Beentje 2016]), oblanceolate or elliptic (vs. lanceolate [sensu Lindley], ovate or narrowly ovate); bracteoles with indumentum abaxially lacking dendritic trichomes (vs. longstalked dendritic trichomes present); corolla lobes adaxially lilac or mauve (pale violet) (vs. heliotrope, magenta or purple-red [bright violet or red]).

Etymology:—The specific epithet refers to the Zebra Mountains (Fig. 1), known as Sebraberge in Afrikaans, located in northwestern Namibia, where Petalidium sebrabergense is exclusively found.

Wessel SWANEPOEL, Abraham E. VAN WYK. 2025. Petalidium sebrabergense (Acanthaceae), A New Species from Namibia. Phytotaxa. 728(1); 17-30. DOI: doi.org/10.11646/phytotaxa.728.1.2 [2025-11-11]

[Botany • 2025] Petalidium saxatile (Acanthaceae) • A New Species from Namibia

Petalidium saxatile  Swanepoel, K.G.Dexter, E.Tripp & A.E.van Wyk,

in Swanepoel, Dexter, Adamo, Manzitto-Tripp et van Wyk. 2025.

 DOI: doi.org/10.11646/phytotaxa.716.3.1

 Abstract

Petalidium saxatile, hitherto confused with P. canescens, and the widespread P. setosum, is here described as a new species. It is a range-restricted species, only known from the vicinity of Palmwag and southwards to the Bergsig area with an outlier population to the south of Khorixas in the Kaokoveld Centre of Endemism, northwestern Namibia. It grows mainly among basaltic rocks of the Etendeka Group on arid hillsides and along ephemeral riverbeds and drainage lines. Diagnostic characters for P. saxatile include the pale green appearance of the plants, vegetative parts with a dense white indumentum of relatively short dendritic trichomes appearing matted on young leaves, flowers borne in compact dichasia, and long simple eglandular trichomes on the bracts visible to the naked eye. The flowers of P. saxatile are distinctive in having the corolla lobes inside (adaxially) distinctly bicolorous: the upper and lateral lobes are pink or brown-pink, while the anterior lobe is yellow. Additionally, all lobes are discolorous in being much paler outside (abaxially). Furthermore, analyses of genetic data across many nuclear loci, generated using a ddRADseq approach, show the species to be genetically distinct from P. canescens. A comparison of key morphological features distinguishing P. saxatile from P. canescens and P. setosum, is provided. Based on IUCN Red List criteria, a provisional conservation assessment of Endangered (EN) is recommended for the new species. It is suggested that the Etendeka Tableland, to which P. saxatile is largely confined, may serve as a local subcentre of plant endemism within the larger Kaokoveld Centre of Endemism, at least for species in the genus Petalidium.

Bergsig, endemism, Etendeka Group, flora, genetics, Kaokoveld Centre of Endemism, Khorixas, Kunene Region, Oberholzeria, Palmwag, RADseq, Ruellieae, taxonomy, Eudicots

Petalidium saxatile, morphology of flowers.
A, B. Newly opened and faded flowers. Anterior corolla lobe inside (adaxially) bright yellow and without nectar guides. C. Flower viewed from above, showing puberulous abaxial surface of posterior corolla lobes. D. Flowers viewed obliquely from above, all corolla lobes discolorous with the outside (abaxial) surfaces puberulous and notably paler in colour. The long white trichomes next to the flower on the right do not belong to the plant, but is a wind-blown feathery awn (arrowed) of a member of the grass genus Stipagrostis.

Photographs by W. Swanepoel.

Petalidium saxatile, habitat and habit.
Note relatively narrow leaves ca. folded upwards along the midrib (B & C). A. Several plants (some arrowed) growing in typical habitat among stones comprising Etendeka Group basalt on an arid hillside. B. Plant with pale grey-green foliage due to a more persistent whitish indumentum, and inflorescences. C. Plant in flower and with greenish foliage resulting from a sparser indumentum.

Photographs by W. Swanepoel.

Petalidium saxatile Swanepoel, K.G.Dexter, E.Tripp & A.E.van Wyk, sp. nov.

 Diagnosis:—A woody dwarf shrub up to 0.5 m tall, morphologically most similar to Petalidium canescens and P. setosum, differing by having indumentum on vegetative parts consisting of simple (weak and robust), bifurcate, stellate-dendritic, dendritic and stalked glandular trichomes, lacking sessile glands (vs. indumentum strigose with in addition widely spaced long, robust, simple trichomes [P. canescens]; long, robust, simple and stalked glandular trichomes, sessile glands present [P. setosum]); leaf lamina conduplicate (vs. flat or subconduplicate [P. canescens]; flat or irregularly curved, twisted, widely undulate, recurved or incurved towards margins [P. setosum]), usually narrower, up to 22 mm wide (vs. up to 100 mm [P. canescens (broad-leaved form)]; up to 50 mm [P. setosum]), with 3 or 4 principal lateral veins each side (vs. 4–6 [P. canescens]; 3–7 [P. setosum]); corolla expanded portion longer, 7.7–9.1 mm long (vs. ca. 7.5 mm [P. canescens]; ca. 3.4 mm [P. setosum]), anterior lobe inside (adaxially) bright yellow, lateral and upper lobes pink or brown-pink, darker towards bases (vs. all lobes similarly coloured: violet-red but anterior lobe darker [P. canescens]; purple, burgundy or carmine, anterior lobe sometimes yellow towards apex [P. setosum]), nectar guides absent (vs. present).

Wessel SWANEPOEL, Kyle G. DEXTER, Martino ADAMO, Erin A. MANZITTO-TRIPP, Abraham E. VAN WYK. 2025. Petalidium saxatile (Acanthaceae), A New Species from Namibia.  Phytotaxa. 716(3); 161-174. DOI: doi.org/10.11646/phytotaxa.716.3.1 [2025-09-03]

[Botany • 2025] Petalidium hoarusibense (Acanthaceae: Ruellieae) • A New Species from northwestern Namibia

Petalidium hoarusibense Swanepoel & A.E.van Wyk, 

in Swanepoel et van Wyk, 2025.  

 DOI: doi.org/10.11646/phytotaxa.681.1.1  

Abstract

Petalidium hoarusibense, hitherto misidentified as P. rossmannianum and P. ohopohense, is here described as a new species. It is a range-restricted species, only known from the area to the south and southeast of Okandjombo in the Kaokoveld Centre of Endemism, northwestern Namibia, where it grows on arid hillsides and along ephemeral riverbeds and drainage lines. Diagnostic characters for P. hoarusibense include the pale grey appearance of the plants, single or multi-stemmed from a thick rootstock, vegetative parts with a dense white indumentum of short dendritic, simple and bifurcate trichomes appearing matted, flowers borne in short, few-flowered dichasia, and bracteoles narrowly ovate or elliptic, deeply concave, appearing cobwebbed due to a mixture of loosely entangled long simple and dendritic trichomes. The flowers of P. hoarusibense are distinctive in having the lobes magenta with the anterior lobe sometimes slightly lighter shaded than the others and with two separate narrowly triangular yellow nectar guides. A comparison of key morphological features distinguishing P. hoarusibense from P. kaokoense, its closest relative in appearance, as well as from P. ohopohense, P. rossmannianum, P. sesfonteinense, and P. welwitschii, is provided. Based on IUCN Red List criteria, a provisional conservation assessment of Vulnerable (VU) is recommended for the new species.

endemism, flora, Kaokoveld, Kaokoveld Centre of Endemism, Kunene Region, Namib Desert, Ruellieae, Okandjombo, Hoarusib River, taxonomy, Eudicots

Petalidium hoarusibense. 
Morphology of leaves and flowers. A. Shoot with flower and leaves, the latter with dense, greyish white indumentum. B, C. Flower in front (B) and side (C) view; note bracteoles (some of spent flowers) with cobwebby indumentum. D, E, F, G. Flowers in front view, each from a different plant to show variation. Note all corolla lobes of a flower being ca. similarly coloured in various shades of magenta, or lateral and upper lobes slightly darker shaded than the anterior lobe, sometimes (as in D, E, G) with darker magenta or maroon triangular nectar guides; anterior lobe adaxially with two narrowly triangular yellow nectar guides.

Photographs by W. Swanepoel.

Petalidium hoarusibense.
Habitat and habit. A. Mature plant ca. 800 mm high (greyish shrub in foreground), growing among dark grey sedimentary rocks of the Swakop Group along the banks of the Hoarusib River near Okandjombo, Namibia. B. Base of plant showing several branches arising from the main stem just above ground level, each covered with rough, fissured, greyish white bark.

Photographs by W. Swanepoel.

Petalidium hoarusibense Swanepoel & A.E.van Wyk, sp. nov.  

Diagnosis:—A woody dwarf shrub up to 1.2 m tall, morphologically most similar to Petalidium kaokoense, from which it differs in having indumentum on the bracteoles cobwebbed, consisting of a mixture of loosely entangled simple and dendritic trichomes up to 2.5 mm long, with in addition scattered short-stalked glandular trichomes (vs. matted/compact, stellate and dendritic, shorter, up to 0.5 mm long, lacking glandular trichomes); corolla glabrous outside (vs. exposed part strigose); nectar guides on anterior lobe narrowly triangular, separate (vs. linear-oblong, confluent or nearly so).

Etymology:—The specific epithet refers to the Hoarusib River and its catchment to which Petalidium hoarusibense is endemic.

Wessel SWANEPOEL and Abrahan E. van WYK. 2025. Petalidium hoarusibense (Acanthaceae), A New Species from Namibia.  Phytotaxa. 681(1); 1-10. DOI: doi.org/10.11646/phytotaxa.681.1.1  

 

[Botany • 2024] Petalidium namibense (Acanthaceae: Ruellieae) • A New Species from Namibia

  Petalidium namibense Swanepoel & A.E.van Wyk,

in Swanepoel et van Wyk. 2024.  

DOI: doi.org/10.11646/phytotaxa.671.2.2 

 

Abstract

Petalidium namibense, hitherto confused with P. englerianum, P. rossmannianum, and the widespread P. variabile, is here described as a new species. It is a range-restricted species, only known from the area to the southwest, west and northwest of Puros in the Kaokoveld Centre of Endemism, northwestern Namibia, where it grows at the base of rocky outcrops, on arid hillsides, and along ephemeral riverbeds and drainage lines. Diagnostic characters for P. namibense include the pale grey appearance of the plants, corky bark on older stems, vegetative parts with a dense white indumentum of relative long dendritic trichomes appearing lanate, flowers borne in short few-flowered dichasia, and bracteoles narrowly ovate. The flowers of P. namibense are distinctive in having the two upper corolla lobes discolorous, abaxially light brown, adaxially vermillion, without nectar guides, and connate towards the base for 25–40% of their length. The anterior lobe is adaxially magenta with two relative long, narrowly triangular yellow nectar guides. The two lateral lobes are adaxially vermillion, or distally magenta, grading to vermillion towards the throat, and lack conspicuous nectar guides. A comparison of key morphological features distinguishing P. namibense from P. sesfonteinense, its closest relative in appearance, as well as from P. englerianum, P. rossmannianum, and P. variabile, is provided. Based on IUCN Red List criteria, a provisional conservation assessment of Vulnerable (VU) is recommended for the new species. 

endemism, flora, Kaokoveld Centre of Endemism, Kunene Region, Namib Desert, Ruellieae, Puros, taxonomy, Eudicots

Petalidium namibense, habitat and habit. 

A. Mature plant (ca. 0.5 m high) with greyish appearance, growing among rocks. 

B. Multiple stems (thickest ca. 80 mm in diam.) from base of a relatively old plant, each covered with thick corky bark.  

Petalidium namibense, habitat and habit. 

A. Several plants (dark grey dwarf shrubs) growing in the bed of an ephemeral drainage line. 

B. Ancient windswept plant sprouting from persistent woody stems with corky bark. 

Photographs by W. Swanepoel.

 Petalidium namibense, morphology of leaves and flowers.
 A. Flower, reduced shoots, and congested leaves; leaves with dense greyish indumentum. B. Flower in the process of fading as indicated by its pale colours. C. Newly opened flower with bracteoles in oblique lateral view; note brownish abaxial colour of posterior corolla lobes. D. Flower in front view. E. Flower with bracteoles in lateral view. F. Flower in dorsal view.

 Photographs: W. Swanepoel.

Petalidium namibense Swanepoel & A.E.van Wyk, sp. nov.  

Diagnosis:—A woody dwarf shrub up to 1 m tall, morphologically most similar to Petalidium sesfonteinense, differing by having the leaf lamina ovate, elliptic, suborbicular or orbicular (vs. ovate, elliptic or oblanceolate); bracteoles with trichomes dendritic, interspersed with glandular ones (vs. trichomes glandular with in addition appressed simple ones towards base); corolla shorter, 15.0–17.5 mm (vs. 20–24 mm long), upper lobes rectangular, smaller, 4.9–5.2 × 2.9–3.2 mm (vs. obovate, 5.8–8.2 × 3.5–4.3 mm), upper and lateral lobes differently coloured than anterior lobe with nectar guides absent or inconspicuous (vs. all lobes similarly coloured, nectar guides on upper and lateral lobes conspicuous).

Etymology:—The specific epithet refers to the Namib Desert to which Petalidium namibense is endemic. The Namib Desert in its broadest definition, stretches along the Atlantic Ocean from Saõ Nicolau (Bentiaba) in Angola through Namibia to the Olifants River in South Africa (Seely 2004, Goudie & Viles 2015).

Petalidium sesfonteinense, morphology of leaves and flowers.
A. Flowers, shoots, and leaves; greyish leaves are still densely covered in trichomes; green leaves almost glabrous. B–E. Flowers in front view showing variation in corolla colour and lobe margins, with two yellow nectar guides.

Photographs: W. Swanepoel. 

Republished from Swanepoel & Manzitto-Tripp (2022).

Wessel Swanepoel and Abraham E. van Wyk. 2024. Petalidium namibense (Acanthaceae), A New Species from Namibia.  Phytotaxa. 671(2); 128-138. DOI: doi.org/10.11646/phytotaxa.671.2.2 

[Botany • 2024] Petalidium etendekaense (Acanthaceae: Ruellieae) • A New Species from Namibia, with Notes on the Taxonomic Identity of P. glutinosum

  

 Petalidium etendekaense  Swanepoel, E.Tripp & A.E.van Wyk,

in Swanepoel, Manzitto-Tripp, Dexter et van Wyk, 2024. 

 DOI: 10.11646/phytotaxa.636.1.3

Photographs by W. Swanepoel.

Abstract

Petalidium etendekaense, previously mistaken for P. glutinosum and P. variabile, is now described as a new species. The name P. pilosibracteolatum is considered synonymous with the older P. glutinosum, the latter of which is also lectotypified. The newly described species is currently only known from the vicinity of Bergsig and slightly further west towards the Skeleton Coast National Park in the Kaokoveld Centre of Endemism, northwestern Namibia. It typically grows on hillsides and along ephemeral riverbeds, primarily in soils derived from Etendeka Group basalt. Diagnostic characters for P. etendekaense include its tomentose-strigulose indumentum, the inflorescence main axis and secondary branches that invariably become spiny with age, and a corolla with an ovate front lobe that is longer than it is wide. Additionally, all lobes of the corolla exhibit similar colours, ranging from dark burgundy to carmine to pink towards the apices. A comparison of some morphological features is provided to differentiate Petalidium etendekaense from P. glutinosum and P. variabile. Based on the IUCN Red List categories and criteria, we conducted a conservation assessment, resulting in the new species being classified as of Least Concern (LC).

Keywords: desert, endemism, flora, Kaokoveld, lectotypification, Ruellieae, Bergsig, taxonomy

 Petalidium etendekaense. Morphology of flowers and leaves.
A, B, C, D. Flowers in front view, each from a different plant to show variation; note all corolla lobes of a flower being similarly coloured. E. Flower and bracteole in lateral view; note absence of long, simple trichomes on bracteoles. F. Flower with bracteoles, viewed from below. G. Shoot showing leaves with dense white indumentum and persistent bracteoles of spent flowers, some enclosing developing fruit.

Scale bar = 3 mm. Photographs by W. Swanepoel.

 Petalidium etendekaense. Habitat and habit.
A. Several plants (foreground and greyish dwarf shrubs in the background) growing on the gently sloping ground between rocky hills in stony soil derived from Etendeka Group basalt. B. Mature plant (ca. 600 mm high) with very short main stem and greyish appearance.

Photographs by W. Swanepoel.

   Petalidium etendekaense. Habitat and habit.
 A. Plant (ca. 350 mm high) with relatively long single main stem, growing among rocks of Etendeka Group basalt. B. Part of fissured greyish white bark on woody stem (ca. 60 mm in diam.) at base of mature plant. C. Plants growing in abundance (right front and low greyish shrublets in background) among rocks of Etendeka Group basalt on a hill slope.

Photographs by W. Swanepoel.

Petalidium etendekaense Swanepoel, E.Tripp & A.E.van Wyk, sp. nov. 

 Diagnosis:—A woody shrub up to 1 m tall, morphologically most similar to Petalidium glutinosum and P. variabile, but differing from both in having indumentum on leaves tomentose-strigulose (vs. strigulose); corolla lobes ascending-spreading with respect to the corolla tube axis (vs. patent or upper lobes in line with tube to sub-patent), lobes all similarly coloured (vs. anterior and sometimes lateral lobes differently coloured or shaded than upper lobes); differing from P. glutinosum in absence of long, simple trichomes on bracteoles abaxially; differing from P. variabile in absence of short geniculate simple trichomes on bracteoles abaxially.

Etymology:—The specific epithet “etendekaense” refers to the Etendeka Tableland landscape (or plateau), which was formed by lava flows (basalts of the Etendeka Group) ca. 132 million years ago due to sea floor spreading and the formation of the South Atlantic. This plateau is a component of a significant igneous province, and its counterpart in Brazil is represented by the Paraná basalts (Goudie & Viles 2015). The name “Etendeka” is derived from the Otjiherero word for layered or stacked, in reference to the flat-topped mountains that define the landscape (Detay & Detay 2017, Atlas of Namibia Team 2022). The entire known population of Petalidium etendekaense is located in this landscape, growing on soils derived from Etendeka basalt.

Wessel Swanepoel, Erin A. Manzitto-Tripp, Kyle G. Dexter and Abraham E. van Wyk. 2024. Petalidium etendekaense (Acanthaceae), A New Species from Namibia, with Notes on the Taxonomic Identity of P. glutinosum. Phytotaxa. 636(1); 35-47. DOI: 10.11646/phytotaxa.636.1.3

[Botany • 2023] Reinstatement of the Name Petalidium ovatum (Acanthaceae: Ruellieae), with an amplified description of the species

Petalidium ovatum (Schinz) Clarke, 

P. englerianum (Schinz) Clarke

in Swanepoel, Dexter, Loiseau et van Wyk, 2023. 

DOI: 10.11646/phytotaxa.626.3.2

 

Abstract

The name Petalidium ovatum is reinstated and an amplified description is provided for a species of Petalidium confined to Namibia. Petalidium ovatum used to be treated as a synonym of the widespread P. englerianum, but morphological characters support the reinstatement. Petalidium ovatum is a range-restricted species, only known from the Khorixas-Bergsig area in the Kaokoveld Centre of Endemism, northwestern Namibia, where it grows on arid hillsides and along ephemeral riverbeds and drainage lines. Diagnostic characters for P. ovatum include the pale grey, often almost white, appearance of the plants, vegetative parts with a dense white indumentum of both stellate and dendritic trichomes, flowers borne in short few-flowered dichasia, bracts oblanceolate with apices acute or obtuse, and bracteoles widely ovate. The flowers of P. ovatum are distinctive in having the anterior corolla lobe partly or completely yellow, the others burgundy, and with the two upper lobes connate towards the base for almost half their length. A comparison of some of the more prominent morphological features to differentiate Petalidium ovatum from P. englerianum, its morphologically most similar relative, is provided. Based on IUCN Red List categories and criteria, a conservation assessment of Least Concern (LC) is recommended for the reinstated species.

Eudicots, desert, endemism, Flora, Kaokoveld, Kaokoveld Centre of Endemism, Kunene Region, Ruellieae, Khorixas, Bergsig, lectotypification, taxonomy

  Petalidium ovatum, habit. 

A. Dwarf shrub, ca. 350 mm high (at Farm Fonteine 717). B. Base of mature plant showing woody stems with fissured greyish white bark (at Farm Fonteine 717).  

Petalidium ovatum, habitat and habit. 

A. Plant (ca. 600 mm high) on arid hillside at Grootberg, highest point on road C39 between Vrede and Bergsig. B. Plant (ca. 500 mm high) in ephemeral riverbed, Farm Inhoek 482, 8 km from Khorixas on road C39. 

Photographs: W. Swanepoel.

Petalidium ovatum, leaf (A) and flower morphology (B–E). 

A. Branchlet with leaves and flowers. B. Flower in front view. C. Flower in lateral view; note widely ovate bracteole with venation ca. visible. D. Flower in front view. E. Flower in lateral view; note bracteoles with indumentum particularly dense and venation not visible.

 Petalidium englerianum, leaf (A) and flower morphology (B–E). 

A. Branchlet with leaves and flower, the latter starting to fade. B. Flower in front view. C. Flower in lateral view. D. Flower in front view. E. Relatively old flower; upper corolla lobes having turned brownish orange as they are fading. 

Photographs: W. Swanepoel.

Petalidium ovatum (Schinz) Clarke (1899: 90) 

Wessel Swanepoel, Kyle G. Dexter, Oriane Loiseau and Abraham E. van Wyk. 2023. Reinstatement of the Name Petalidium ovatum (Acanthaceae), with an amplified description of the species.  Phytotaxa. 626(3); 159-169. DOI: 10.11646/phytotaxa.626.3.2

[Botany • 2023] Sesamothamnus leistneri (Pedaliaceae: Sesamothamneae) • A New Species from Namibia and Angola

Sesamothamnus leistneri P.Craven ex Swanepoel & A.E.van Wyk,
 

in Swanepoel et E. van Wyk, 2023.

DOI: 10.11646/phytotaxa.626.3.1

Abstract

Sesamothamnus leistneri is formally described as a new species with a restricted range, only known from the mountains along the Kunene River in the Kaokoveld Centre of Endemism, a biogeographical region that spans southwestern Angola and northwestern Namibia. The designations “S. leistner(i)anus” or “S. leistneri” have been previously used to refer to this species, but they were not validly published until now. These trees grow in rocky places on mountain slopes, in kloofs (gorges) and on plateaus. Diagnostic characters for S. leistneri include the pronounced tree habit with thickset semi-succulent stem and branches, relatively large green leaves, the corolla lacking a spur, and flowers with a white to cream-white corolla limb. A comparison of some of the more prominent morphological features to differentiate between S. leistneri and its possibly closest relative, S. rivae, as well as the other four species, S. benguellensis, S. guerichii, S. lugardii, and S. busseanus are provided. Based on IUCN Red List categories and criteria, a conservation assessment of Least Concern (LC) is recommended for S. leistneri.

Keywords: Eudicots, endemism, flora, Iona National Park, Kaokoveld Centre of Endemism, Kunene Region, Sesamothamneae, sphingophily, taxonomy

Sesamothamnus leistneri, fruit morphology. A. Two almost mature fruit and a dehisced one. B. Old dehisced fruit persist for some time on trees. 

Photographs by W. Swanepoel (A) and A.E. van Wyk (B).

Sesamothamnus leistneri, flower morphology. A. Inflorescence showing one open flower, several flowers in different stages of development, and persistent styles (whitish, tipping blackish ovaries) of faded flowers following shedding of the corolla. B. Flowers, open and in bud; note both stamens and stigma positioned in mouth of the corolla tube, also the lack of a spur at the base of the tube. C. Flower showing style with bilobed stigma exserted about 10 mm from the mouth of the corolla tube. D. Distal part of corolla tube opened out to show the yellow inner surface of the tube, white filaments, and anthers positioned at the level of the corolla mouth. 

Photographs by W. Swanepoel (A, B, D) and A.E. van Wyk (C).

Sesamothamnus leistneri, vegetative morphology. A. Single-stemmed tree showing ± fluted trunk. B. Bark peeling in papery pieces. C. Long shoot with leaves clustered on lateral short shoots. D. Mature leaves showing green colour and ± glossy upper surface. E. Long shoot with spines derived from petioles; one dried leaf blade still attached.

Photographs by A.E. van Wyk (A, E) and W. Swanepoel (B–D).

Sesamothamnus leistneri P.Craven ex Swanepoel & A.E.van Wyk, sp. nov.

Diagnosis:—Single or usually multi-stemmed succulent tree, morphologically most similar to Sesamothamnus rivae, differing by being up to 8 m tall with high succulence of main stems (vs. small multi-stemmed tree up to 3 m tall, low succulence of main stems), flowers lacking a spur (vs. spur present), and flowering during the rainy season with developed leaves (vs. flowering before onset of rainy season when plants still leafless).

Etymology:—The specific epithet honours Otto Albrecht Leistner, who, together with Bernard de Winter, first collected Sesamothamnus leistneri in 1957 during an epic collecting trip to the Kaokoveld (Leistner 2022). In our choice of name, we have chosen to use the epithet as a noun in the genitive case (“leistneri”) rather than an adjective (“leistnerianus”). Either of these options have been used to designate the taxon in the past. We consider the genitive case to be more appropriate, as it indicates that this species is Leistner’s particular discovery, not anybody else’s

Wessel Swanepoel and Abraham E. van Wyk. 2023. A New Species of Sesamothamnus (Pedaliaceae) from Namibia and Angola.  Phytotaxa. 626(3); 145-158. DOI: 10.11646/phytotaxa.626.3.1

[Botany • 2023] Petalidium karasbergense (Acanthaceae: Ruellieae) • A New Species from Namibia

Petalidium karasbergense  Swanepoel & A.E.van Wyk,

in Swanepoel et van Wyk, 2023.

DOI: 10.11646/phytotaxa.609.1.1

Photographs by W. Swanepoel.

Abstract

Petalidium karasbergense, here described as a new species, is only known from the Groot Karasberge (Great Karas Mountains) in southeastern Namibia where it grows on arid hillsides in dwarf shrubland. Diagnostic morphological characters for P. karasbergense include the rigid, tapering and often spinescent distal stems and lateral branchlets, grey, grey-white or grey-black bark (white to cream when young), strigulose, glabrescent vegetative parts, oblanceolate to narrowly obovate leaves, and the free to almost free bracteole pairs (not connate at the base). A comparison of some of the more prominent features to differentiate Petalidium karasbergense from P. parvifolium, its morphologically most similar relative, and P. lucens with which its distribution range marginally overlaps, is provided. Based on IUCN Red List categories and criteria, a conservation assessment of Vulnerable VU D1 is recommended for the new species.

Keywords: desert, endemism, flora, Great Karas Mountains, Groot Karasberge, Petalidium lucens, Petalidium parvifolium, Ruellieae, taxonomy

Petalidium karasbergense, morphology of flowers, stems, and leaves. A. Flower in front view. B. Flower with bracteoles in lateral view. C. Flower viewed from below; note the bracteoles that are not connate at the base, hence the calyx is clearly visible over the whole of its length. D. Branchlet showing an open flower, persistent bracteoles, and leafy side shoots (some tapering to a spinescent tip). E. Enlarged portion of Auret 5617 in Herb. PRE showing three brachyblasts, the longest one with several phyllopodia, the latter each ca. 1 mm long.

Photographs by W. Swanepoel (A–D) and A.E. van Wyk (E).

Petalidium karasbergense Swanepoel & A.E.van Wyk, sp. nov. 

Diagnosis:—A woody dwarf shrub up to 1 m tall, morphologically most similar to Petalidium parvifolium, differing in having the distal stems and lateral branchlets tapering to a blunt or spinescent apex (vs. cylindric); indumentum on vegetative parts strigulose (vs. scattered sessile glandular trichomes); young growth not glutinous (vs. covered with a glutinous secretion [glossy]); leaf lamina subconduplicate towards recurved apex (vs. flat or subreduplicate, apex slightly recurved); bracteoles free or almost free from base (vs. distinctly connate towards base), indumentum (abaxially) on bracteoles strigulose (vs. scattered sessile glands, towards base sometimes with very short stalked glandular trichomes in addition).

Petalidium karasbergense, habitat and habit. A. Plant (ca. 50 cm high) with open flower. B. Old, stunted plant showing thick, woody stem (ca. 8 cm in diameter). C. Mature plant (ca. 80 cm high) in habitat; surrounded by sandstone rocks of the Nama Group.

Photographs by W. Swanepoel.

Etymology:—The specific epithet refers to the Groot Karasberge in southeastern Namibia, the mountain complex to which the new species is confined.

Wessel Swanepoel and Abraham E. van Wyk. 2023. Petalidium karasbergense (Acanthaceae), A New Species from Namibia.  Phytotaxa. 609(1); 1-9. DOI: 10.11646/phytotaxa.609.1.1

 

[Botany • 2023] Petalidium konkiepense (Acanthaceae: Ruellieae) • A New Species from southern Namibia

Petalidium konkiepense  Swanepoel & A.E.van Wyk, 

in Swanepoel & van Wyk. 2023. 

 DOI: 10.11646/phytotaxa.585.1.3

Abstract 

Petalidium konkiepense, here described as a new species, is only known from the Gariep Centre of Plant Endemism in southern Namibia, where it grows on arid hillsides and along drainage lines. Diagnostic morphological characters for P. konkiepense include the rigid, cylindrical distal stems (quadrangular when young), grey or dark brownish grey bark (white to cream when young), densely puberulent vegetative parts with widely spaced robust glandular and eglandular trichomes, and the oblanceolate leaves with prominent midrib and principal lateral veins. A comparison of some of the more prominent features to differentiate Petalidium konkiepense from its morphologically most similar relatives, P. linifolium and P. cymbiforme, is provided. Based on IUCN Red List categories and criteria, a conservation assessment of Endangered under criteria B1 is recommended for the new species. 

Keywords: desert, endemism, flora, Gariep Centre, Ruellieae, taxonomy

Petalidium konkiepense, habitat and habit.
A. Plant in flower (right foreground) with several 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.

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.

Petalidium konkiepense Swanepoel & A.E.van Wyk, sp. nov.

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).

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.

 

Wessel Swanepoel and Abraham E. van Wyk. 2023. Petalidium konkiepense (Acanthaceae), A New Species from Namibia. Phytotaxa. 585(1); 29–38. DOI: 10.11646/phytotaxa.585.1.3