Zehneria palmatiloba O.Lachenaud & H.Schaef., 2021

Lachenaud, Olivier & Schaefer, Hanno, 2021, Zehneria palmatiloba, a new species of Cucurbitaceae from Atlantic Central Africa, Phytotaxa 496 (2), pp. 170-178 : 172-176

Zehneria palmatiloba O.Lachenaud & H.Schaef. , sp. nov. ( Fig. 2 & 3A )

Lamina profunde 5–7-palmatilobata conspicue differt ab omnibus congeneribus Z. racemosae Hook. f. excepta , a quae lamina non scabra, inflorescentiis foemineis laxe racemosis (nec congestis), floribus masculis minoribus receptaculo 0.8–1.2 × 1.2–1.8 mm intus glabro (nec 1.5–2.0 × 1.5–2.0 mm intus pubescente) distinguitur.

Type: — EQUATORIAL GUINEA. Rio Muni : Bata - Senge - Senge 1°: estrada km. 42–43, población de Senge 1°a estrada de la empresa maderera SINOSA, ♂ fl., 5 May 1997, M. F . de Carvalho 6307 (holotype, BR! [ BR0000009254718 ]; isotypes, MA!, WAG! [ WAG.1524509]) .

Herbaceous climber, apparently dioecious. Stems very slender (c. 0.5 mm thick), angular when dry, glabrous or very sparsely papillate-hairy. Leaves with petiole 1.5–4.0 cm long, glabrous or with very short sparse hairs; lamina deeply 5- to 7-palmatilobate, 2.5–6.0 × 2.0– 5.5 cm, cordate at base, lobes unequal (basal ones smaller), obovate to rhomboid, constricted at base, usually bearing 1 to 2 small lateral teeth on each side and sometimes lobulate, apex obtuse with short mucro; both surfaces of leaf blade densely pustulose (only slightly so when fresh, much more conspicuously so when dry) but not markedly scabrid, glabrous except veins that have minute appressed hairs, drying dark green (lower side paler); venation palmate with 5–7 basal veins reaching apex of lobes, slightly raised above in life, larger lobes showing 1–3 pairs of flat secondary veins; tertiary venation invisible; basal glands absent. Tendrils simple, 1.5–12.0 cm long, coiled in spiral for most of their length. Male inflorescences axillary, 1–3 cm long, racemose, glabrous except minute hairs at nodes, very slender peduncle 0.7–2.3 cm long, 7–20 flowers subumbellately arranged; bracts absent. Male flowers: pedicel 1–3 mm long, slender, glabrous, articulate at apex; receptacle cupuliform, 0.8–1.2 × 1.2–1.8 mm long, glabrous on both sides; sepals deltoid, hardly distinct; corolla divided almost to base into 4–5 triangular lobes c. 0.5 mm long, puberulous outside, glabrous inside; stamens 3, included; filaments c. 0.5 mm long, glabrous; anthers 2-celled, reniform, c. 0.4 × 0.6 mm, papillose; rudimentary ovary domed, c. 0.5 mm high, glabrous. Female inflorescences axillary, 3.5–7.5 cm long, racemose (sometimes grouped in terminal pseudopanicles), glabrous except minute hairs at nodes, peduncle 1.7–6 cm long, 4–7 widely spaced flowers, all axes very slender; bracts absent or minute. Female flowers: pedicel 8–11 mm long, very slender, glabrous, articulate at apex; receptacle urceolate, c. 1 × 2.3 mm, glabrous on both sides; sepals deltoid, hardly distinct; corolla divided nearly to base into 5 triangular lobes, 0.8–1.2 × 0.6–1.0 mm, glabrous outside, papillose inside; staminodes 5, linear, c. 0.5 mm long; ovary ovoid, c. 2 × 1 mm long, glabrous, with c. 16 horizontal ovules; disk entire, cylindrical, c. 0.5 mm, glabrous; styles 3, connate at base, c. 1 mm long, glabrous, with capitate stigma. Fruits globose, 8–11 mm in diameter when dry, glabrous, on pedicel 9–14 mm long. Seeds compressed, obovoid in outline, c. 5 × 3 mm, whitish, ± smooth, margin hardly thickened.

Distribution and Ecology:— The species occurs in the continental part of Equatorial Guinea ( Rio Muni) and in the Cristal Mountains in adjacent northwest Gabon ( Fig. 4 ). It could be expected in southern Cameroon, but has not been recorded there so far. It occurs in primary rainforest, often along creeks, and is apparently restricted to very wet areas near the foot of mountain ranges. Though it may be abundant in places, it seems to be very local, having not been found in many apparently suitable sites.

Phenology:— Flowers in May and November; fruits in November.

Conservation status assessment:— Endangered [EN B1ab(i,ii,iii,iv,v) & B2ab(i,ii,iii,iv,v)]. Zehneria palmatiloba occurs in Equatorial Guinea and northwest Gabon and is known from four collections, representing four distinct occurrences. Its extent of occurrence (EOO) and area of occupancy (AOO) are estimated to be 3 054 km² and 16 km ² respectively, which both fall within the limit for Endangered status under subcriteria B1 and B2. The species is not known from any protected areas, though it is likely to occur in Monte Alén National Park ( Equatorial Guinea) and Monts de Cristal National Park ( Gabon), having been collected very close to their limits. Its only occurrence in Gabon is in an area scheduled for a dam project, which, if carried out, will represent a threat to its habitat. The three occurrences in Equatorial Guinea are situated near roads, and therefore exposed to deforestation for agriculture, which is ongoing in the area. For these reasons a decline in the EOO, AOO, habitat extent and quality, number of subpopulations and number of individuals is expected. The four occurrences represent four locations in the sense of IUCN (2012) and the species is assessed as Endangered according to the conditions B1ab(i,ii,iii,iv,v) & B2ab(i,ii,iii,iv,v).

Notes:— The 5- to 7-palmatilobate leaves of this species are very unusual in the genus and unique among Central African species. The leaves of the Angolan endemic Zehneria racemosa may also be palmatilobed, but are very scabrous; the two species additionally differ in numerous characters ( Table 1) and are genetically distinct ( Fig. 1 ). From Z. keayana , which is its closest relative, the new species also differs in many characters of the flowers and inflorescences in addition to leaf shape ( Table 1).

As noted above, leaves of Zehneria palmatiloba closely resemble in shape those of Momordica charantia , and the two species have been mistaken for this reason. In the vegetative state, M. charantia differs from Z. palmatiloba by its leaf lobes that have several marginal teeth on each side (only 1 to 2 in Z. palmatiloba ), and its smooth upper leaf surface, with primary and secondary veins both distinctly impressed (in Z. palmatiloba the upper leaf surface is pustulate, especially in the dry state, with primary veins raised and secondary veins flat). These differences are illustrated in Fig. 3 . The two species are quite different when fertile, M. charantia having much larger solitary flowers with yellow petals, a broad foliaceous bract on the pedicel, large ovoid tuberculate fruits that are dehiscent at maturity, and larger sculptured seeds surrounded with a red pulp.

The only collection of Z. palmatiloba from Gabon is vegetative, but its identity is without doubt, since the leaves are very characteristic, and the ecology and distribution are coherent with the Equatorial Guinea specimens. The hill ranges of central Equatorial Guinea and the Cristal Mountains in northern Gabon are indeed very close biologically, and are often regarded as part of the same massif (e.g. Senterre 2005). This area is among the most diverse botanically in tropical Africa ( Sosef et al. 2017) and regularly yields new species (e.g. Leal 2007, Champluvier & Senterre 2010, Lachenaud & Breteler 2011, Barberá et al. 2015, Couvreur & Niangadouma 2016, Veranso-Libalah et al. 2019, Liang et al. 2020, Lachenaud et al. 2020). Botanical collecting efforts in this region have been intensive, but mostly concentrated on a few well-known sites along main roads, while significant areas, such as the western foothills of the Cristal Mountains, are still relatively little-known.

Additional material studied (paratypes):— EQUATORIAL GUINEA ( Rio Muni ). Bata - Niefang: estrada km 35, entrada a la zona de Comaya, ♀ fl. & fr., 24 November 1994, M. F . de Carvalho 5709 ( BRLU, MA, WAG); Route de Nco vers Misobong au niveau de la grande cascade, ♂ fl. (fallen), 9 January 1998, N . Nguema & J . Lejoly 199 ( BRLU). GABON. Rive ouest de la Mbei entre Kinguélé et Andok Foula (site du barrage en projet), st., 20 October 2020, O . Lachenaud, I . Nguimbit, A.- H . Paradis, E . Akouangou, E . Bidault & J . Kaparidi 3055 ( BR, BRLU, LBV, MO, WAG) .

Figures

FIGURE 1. Maximum likelihood phylogeny estimate for the genus Zehneria inferred with RAxML based on 925 nucleotides of the nuclear ribosomal ITS region plus 4314 nucleotides of five plastid DNA regions (rbcL gene, matK gene, rpl20-rps12 spacer, trnL intron, trnL-trnF spacer). Likelihood bootstrap values ≥ 65% are shown at the nodes. The arrow indicates the position of Zehneria palmatiloba from Equatorial Guinea. Other West African accessions are marked in green. The scale bar indicates the number of substitutions per site per million years.

FIGURE 2. Zehneria palmatiloba. A. Stem with male inflorescences. B. Male inflorescence (most flowers fallen). C. Male flower. D. Longitudinal section of male flower. E. Fragment of stem with female inflorescences. F. Female flower. G. Longitudinal section of female flower (without the ovary). H. Fruit. I. Seed. From Carvalho 6307 (A–D) and Carvalho 5709 (E–I). Drawing by O. Lachenaud.

FIGURE 3. Leaves of Zehneria palmatiloba (A) and Momordica charantia (B), seen from above, for comparison. From Lachenaud et al. 3055 (A) and plant not collected, Kourou, French Guiana, December 2015 (B). Photos: O. Lachenaud.

FIGURE 4. Known distribution of Zehneria palmatiloba. Areas above 500 m in elevation are in dark grey.