Impatiens pinganoensis Abrah., S.B.Janssens, Xixima, Ditsch & Eb.Fisch., 2016

Abrahamczyk, Stefan, Janssens, Steven, Xixima, Lázaro, Ditsch, Barbara & Fischer, Eberhard, 2016, Impatiens pinganoensis (Balsaminaceae), a new species from Angola, Phytotaxa 261 (3), pp. 240-250 : 243-249

Impatiens pinganoensis Abrah., S.B.Janssens, Xixima, Ditsch & Eb.Fisch. , sp. nov. ( Fig. 1 , 2 )

Impatienti filicornu affinis sed petiolo decurrente, regulas suberosas crescentibus, petalis superioribus lateralibus petalos inferiores superantibus, floribus albis centro violaceo et petalibus lateralibus superioribus maculis purpureis instructis valde differt.

Type:— ANGOLA Uíge, Serra do Pingano, near Bem Vindo , S 7°41’7.35”, E 14°55’46.9”, 930 m, ( Fig 3 ), Barbara Ditsch, BD 546a (holotype LUA! ( Fig. 4 ); isotype DR!.

Decumbent to slightly ascendant, perennial herb, up to 20(–25) cm high. Stems strongly branching, rooting at and in between the lower nodes. Plant entirely glabrous. Leaves spirally arranged, deep green above, pale green below; the main veins, petioles and inflorescences reddish; the petiole base decurrent, developing into cork ridges at older stems; the petiole 10–40 mm long, continuously growing. Lamina (60–) 80–102 mm x (30–) 38–52 mm, leathery, elliptic to lanceolate, the apex acute, the basis shortly attenuate; lateral veins 4–5(–6) pairs; margin crenate; extrafloral nectaries 1–2 mm, linear, at the lamina margin between each pair of teeth and at the tip of the apex, half erect, prominent especially at young leaves. Inflorescence a (4–)8 flowered raceme. Flowers white with mauve centre and wing-like pattern on the upper lateral petals and occasionally a pair of small pink dots on the upper part of the lower lateral petals. Peduncle 37–130 mm long, upright. Bracts 6–7 mm x 3–4 mm, ovate-lanceolate. Pedicels 6–11 mm long, slender, continuously growing until fruit ripeness to 12–15(–20) mm. Lateral sepals 2, 3–4 mm x 1.5–2 mm, ovate-lanceolate, acute. Lower sepal 3–4 mm long, 4–6(–7) mm deep, obliquely naviculate, white, abruptly peaking into a light greenish, 1 mm down facing tip and abruptly constricted into an (8–) 13–17 mm, broad, curved, filiform, white, pinkish overflown spur with obtuse apex. Dorsal petal 6–8 mm x (3–) 4–5 mm, ovate-lanceolate, acute, helmet-like, folded, dorsally with a narrow, light greenish crest. Lateral united petals (10–) 12–14 mm long, with petals different in size and shape; upper petal 9– 10(–11) mm x 3–4(–5) mm, falcate to narrowly-oblong; lower petal 9–10(–12) mm x 5–7 mm, suborbicular to oblong, distally drawn out along the inner margin into a 3–4 mm x 2–3 mm ligulate appendage. Appendages overlapping to spreading. Ovary glabrous. Fruit 12–15 mm x 4–5 mm, fusiform, glabrous, producing 5–21 ovate, smooth seeds of 2 mm x 1 mm having a tuff of numerous, dead, spiral hairs at the hilum and few additional ones at the narrow side of the seeds. Hairs tear along the spirally thickened cell walls developing into relatively tear-resistant, spiral fibres.

Habitat: —On clastic sedimentary rocks of quartz or other silicate minerals (Direcção dos serviços de geologia e minas 1980) at the spray zone of a creek, 930 m.

Distribution: — Angola, Uíge, Serra do Pingano, Bem Vindo, only known from the type collection and the cliffs of a waterfall nearby (S 7°40’22.7”, E 14°56’17.7”, 615 m; Fig. 3 & 5 ).

Phenology: —Flowers and fruits in its habitat during the rainy season (October to April). Data for the dry season are not available. In greenhouses in the Botanical Gardens of Bonn and Dresden, it flowers and fruits around the year, especially between April and October.

Etymology: —Named after the Serra do Pingano, a mountain range in northern Angola.

Conservation status:— We suggest to categorize the new species as critically endangered (CR) since it has a very limited distribution range and occurs only in the cliffs of two waterfalls with a very special microclimate. This habitat is endangered by deforestation and a planned construction project.

Additional specimens examined (paratypes):— Angola, Uíge, Serra do Pingano, Bem Vindo, S 7°40’22.7”, E 14°56’17.7”, 615 m Anne Göhre 25/2015 a–f, P!, B!, BR!, BONN!).

The new species is part of the Impatiens filicornu complex and closely related to I. filicornu occurring from Cameroon to the Democratic Republic of Congo. The internal, phylogenetic relationships of this group of seven species have not been investigated, yet. Impatiens filicornu sensu Grey-Wilson (1980) comprises apparently several undescribed taxa, which are currently studied by the authors. However, Impatiens pinganoensis , the southernmost, local endemic representative differs from all other species of the I. filicornu complex by several characters ( Tab. 1; Fig. 6 ) and has probably been isolated from the populations of I. filicornu , the closest relative further north during the drying up of tropical Africa since the last ice ages.

Cork ridges, first considered to be a unique character of Impatiens pinganoensis , have already been observed by Weber (1949) in I. sultani Hook.f. (1882: pl. 6643) (= I. walleriana Hook.f. (1868: 302) . Weber (1949) states that the small, weak and irregular cork ridges are formed by the epidermis by transforming the epidermis cells to phellogene which protrude towards the outside.

During field observations in the Serra do Pingano a long-proboscid fly ( Empis sp. , Empididae ; Fig. 7 ) was observed legitimately visiting and pollinating the flowers of Impatiens pinganoensis . Additionally, pollination by lepidoptera seems also possible, since both pollinator groups visit flowers with the same flower morphology, which has already been observed for Impatiens hochstetteri in South Africa ( Potgieter & Edwards 2005).

Cultivating the plants, the hairs at the hilum and at the narrow side of the seeds were observed to be tearing along the spirally thickened cell walls developing into relatively tear-resistant, spiral fibres ( Fig. 8 ), which probably serve to attach the seeds to passing distributers ( Hilger 1983) as well as to the stones of the cliffs where Impatiens pinganoensis occurs.

Figures

FIGURE 1. Impatiens pinganoensis. A, habit. B, flower, frontal view, C, inflorescence, lateral view, D, lateral sepal, E, lower sepal and spur, F, dorsal petal, G, H, lateral united petals. All drawn from the type by E. Fischer.

FIGURE 2. Impatiens pinganoensis.A, habit with inflorescence. B–D, young inflorescence with flower; E, flower; F, inflorescence with flower and young fruits. A–E, phot. E. Fischer, Botanical Gardens University of Bonn. F, phot. B. Ditsch.A: Scale bar 1 cm, B–F: 5 mm.

FIGURE 3. Distribution map of Impatiens pinganoensis.

FIGURE 4. Holotype specimen of Impatiens pinganoensis, phot. B. Ditsch.

FIGURE 5. A–C, Habitat of Impatiens pinganoensis, phot. B. Ditsch.

FIGURE 6. A–D, Transections of the cork ridges at the older stems showing numerous rhaphides, phot. E. Fischer. A: Scale bar 1 mm, B–C: 0.1 mm, D: 0.2 mm.

FIGURE 7. Pollinator (Empis sp.) of Impatiens pinganoensis, phot. B. Ditsch.

FIGURE 8. Seed hairs with spirally thickened cell walls developing into relatively tear-resistant, spiral fibres, phot. M. Günther.