Drypetes gabonensis Pierre ex Hutch.

Quintanar, Alejandro, Harris, David J., Nguema, Diosdado & Barberá, Patricia, 2023, Notes on cauliflory, sexual dimorphism and biogeography in Drypetes (Putranjivaceae, Malpighiales) and a taxonomic treatment for D. gabonensis and two new cauliflorous threatened species from Central Africa, D. aphanes sp. nov. and D. cauta sp. nov., European Journal of Taxonomy 888, pp. 175-202 : 180-186

Drypetes gabonensis Pierre ex Hutch.

Fig. 2

Flora of tropical Africa 6 (1): 680 ( Hutchinson 1912). –

Type: GABON • [Estuaire, environs de Libreville ]; [0º25′N 9º27′E]; 18 Jul. 1898; T.J. Klaine 1278; fr.; lectotype, here designated: P [ P04707398 ]; isolectotypes: BR [ BR0000006238124 , BR0000006238452 , BR0000006238780 (BR-S.P. 623 878)], K [ K000406326 ], P [ P04707401 ].

Etymology

The specific epithet is the Neolatin adjective ‘ gabonensis ’, which refers to Gabon, the country in which the first gatherings of this species were made and therefore from which it was originally known.

Material examined

ANGOLA – Cabinda • Along the river Lufo, Hombe region, Maiombe , area de Belize ; [4º46′ S, 12º36′ E]; Mar. 1919; J. Gossweiler 8227; fl. ♂; BM, BR [ BR0000015778390 , BR0000015778406 , BR0000015778413 ], COI [ COI00033993 ], K, LISC [ LISC053291 , LISC053294 ], LISU [ LISU 60111 , LISU 60112 ] • Near Caio, Hombe region, Rio Lufo ; [4º46′ S, 12º36′ E]; 26 Feb. 1919; J. Gossweiler 7859; fl. ♂; BM, COI [ COI00033992 ], LISC [ LISC053287 , LISC053306 , LISC053307 , LISC053308 ], LISU [ LISU 60106 , LISU 60113 ] • Near the village Caio, Hombe region, Río Lufo, Maiombe ; [4º46′S 12º36′E] 8 Apr. 1919; J. Gossweiler 7985; fr.; BM, COI [ COI00033990 ], LISU [ LISU 60109 , LISU 60108 ] • Río Lufo, Caio, Hombe region, Maiombe ; [4º46′ S, 12º36′ E]; 27 Mar. 1919; J. Gossweiler 7956; fl. ♂; BM, COI [ COI00033991 ], LISC [ LISC053298 , LISC053299 , LISC0532301 , LISC0532302 , LISC0532305 ], LISU [ LISU 60107 , LISU 60110 ] • Portuguese Maiombe, Chiloango ; [5º1′S, 12º25′ E]; 1919; J. Gossweiler s.n.; fl. ♂; K.

CAMEROON – East Region • Bertoua , near catholic mission; [4º35′ N, 13º40′ E]; 15 Dec. 1960; F.J. Breteler 829; fl. ♂; A n.v., BR [ BR0000015788429 ], BRLU [ BRLU0000145 ], FI n.v., K, M [ M 257127 ], P [ P04707288 ], WAG [ WAG.1563830 , WAG.1563831 ], YA [ YA 29609 ] • Bertoua , near catholic mission; [4º35′ N, 13º40′ E]; 7 Sep. 1961; F.J. Breteler 1897; fr.; BRLU [ BRLU0000144 ], WAG [ WAG.1563827 , WAG.1563829 , WAG.1563828 ]. – South Region • About 7 km NE of Ebom , plot 19, subplot 47, tree 2; 3º7′ N, 10º45′ E; Aug. 1996; M.P.E. Parren 268; veg.; KRIBI, WAG [ WAG.1564719 ] • ibid., plot 19, subplot 59, tree 5; 3º7′ N, 10º45′ E; Aug. 1996; M.P.E. Parren 277; veg.; KRIBI, WAG [ WAG.1564749 , WAG.1564750 ] • ibid., plot 9, subplot 69, tree 5; 3º7′ N, 10º45′ E; Aug. 1996; M.P.E. Parren 122; veg.; KRIBI, WAG [ WAG.1564714 , WAG.1564715 , WAG.1255335 ] • ibid., plot 9, subplot 89, tree 5; 3º7′ N, 10º45′ E; Aug. 1996; M.P.E. Parren 141; veg.; KRIBI, WAG [ WAG.1564712 , WAG.1564713 ] • Ebolowa-Jaunde [südl. des Njong , Amugebane-Nkolemajang ]; [3º15′ N, 10º59′ E]; Jan. 1914; G.W.J. Mildbraed 7672; fl. ♂; BR [ BR0000015785268 , BR0000006576394 (BR-S.P. 657 639)], K [ K000406365 ].

EQUATORIAL GUINEA – Centro-Sur • Parc National de Monte Alén, transect de Monte Chocolate ; 1º39′N 10º19′E; 14 Jul. 1995; J. Lejoly 95T/L3.647; veg.; BRLU.

GABON – Estuaire • T.J. Klaine 1278 (type, see above) • Environs de Libreville ; [0º25′N 9º27′E]; Jul. 1897; T.J. Klaine 690; fr.; BM, P [ P04707286 , P04707289 ], WAG n.v.) • Environs de Libreville ; [0º25′ N, 9º27′ E]; 18 Jul. 1898; T.J. Klaine 1034; fl. ♂, ♀, fr.; K [ K000406329 , K000406330 ], P [ P04707273 , P04707274 , P04707275 ], WAG n.v. • Environs de Libreville ; [0º25′ N, 9º27′ E]; 18 Jul. 1898; T.J. Klaine 182; fl. ♀; K, P [ P04707843 , P04707845 , P04707847 ] • Environs de Libreville ; [0º25′ N, 9º27′ E]; 20 Jul. 1901; T.J. Klaine 437; fl. ♂, fr.; P [ P04777141 , P04777142 ], WAG n.v. • Environs de Libreville ; [0º25′ N, 9º27′ E]; 18 Jul. 1898; T.J. Klaine 1034bis; fl. ♂; BR [ BR0000006239091 ], K [ K000406327 , K000406328 ], P [ P04707402 , P04707403 , P04707404 ] • Environs de Libreville ; [0º25′ N, 9º27′ E]; 17 Dec.1902; T.J.Klaine 3188;fr.; P [ P04707399 ], WAG n.v. • Environs de Libreville ;[0º25′N, 9º27′ E]; 26 Aug. 1896; T.J. Klaine 551; fr.; P [ P04707278 , P04707279 , P04707280 , P04707282 , P04707283 ], WAG n.v. – Ogooué-Ivindo • Forêt des Abeilles , 7 km SE of confluence Ogooué-Ivindo; 0º13′ S, 12º14′ E; 7 Aug. 1993; J. Dibata 1174; fl. ♀; BR[ BR0000016221437 ], MA [ MA 579857 ], MO [ MO 05016606 ], WAG [ WAG.1255159 ] – Ogooué-Lolo • Région de Lastoursville, Mouila ( Poubi ); [1º19′S 12º11′E]; 2 Aug. 1930; G.M.P.C. Le Testu 8214; fl. ♂; G n.v., K, MO [ MO 5709020 ], P [ P04707816 , P04707817 ], WAG [ WAG.1579080 , WAG.1579081 ].

REPUBLIC OF THE CONGO – Lékoumou • Chantier forestier de M. Fouet , Moussoumou , 35 km E of Sibiti ; 3º45′S 13º35′E; 18 Aug. 1965; C. Farron 4469; fl. ♂; MO [ MO 5558745 ], P [ P04707281 , P04707284 , P04707285 ] – Sangha • [Ouésso] Layon 2252-piquet 223; unknown coordinates; 7 Jan. 1970; Ledreau 55; veg.; P [ P04707758 ].

Description

Tree to 30(‒35) m, with plagiotropic branches and a dense crown, dioecious; trunk to 50 cm in diameter, upright or leaning, more or less cylindrical at the base, bark smooth, pale greenish-brown to pale greyish-brown, branchlets terete to slightly flattened, sulcate, glabrescent, with few scattered trichomes to 0.1 mm; apical buds scaly, scales 2‒2.4 × ca 0.5 mm, narrowly triangular, densely and minutely pubescent outside, trichomes to 0.1 mm. Leaves simple, alternate, glossy and dark-medium green above, dull and paler beneath; stipules ca 1.8(‒3) × 0.4 mm, ovate, deciduous, falling very early, densely and minutely pubescent outside, glabrous inside, trichomes to 0.1 mm; petiole (4.2‒)7.7‒9.6(‒13.1) mm long, (1.1‒)1.4‒1.8(‒2.3) mm in diameter, smooth, becoming coarsely wrinkled and bullate when old, channeled above, drying blackish, glabrous, exceptionally sparingly and minutely pubescent, trichomes to 0.1 mm; blade (10.3‒)12.8‒17.8(‒21.7) × (3.4‒)4.4‒5.8(‒8.9) cm, narrowly to widely elliptic or oblong, sometimes wider at distal half, coriaceous, shortly and abruptly acuminate, frequently cuspidate, apex (5‒)8.3‒11.1(‒12) mm, base acute to slightly obtuse, markedly asymmetrical, rounded on one side, less often oblique, basal sides often meeting the petiole at different points up to 1.6 mm apart, margin subentire to shallowly and obscurely crenulate-serrulate, mostly towards the leaf apex, crenulae to 0.3 mm, flat to slightly recurved, frequently undulate, underside of the lamina glabrous; midrib longitudinally slightly wrinkled when dry, glabrous, first order lateral veins 6‒8(‒9) pairs, ascending, more or less regularly spaced, slightly depressed above, prominent beneath, obscurely diminishing and anastomosing near the margin, forming angles of 58‒74º to the midrib, glabrous, second order venation slightly raised above and beneath. Male inflorescence clusters borne axillary on leaf and leafless branches (categories III and IV), to ca 25(‒50) flowers, often in much smaller numbers; bracts 0.2‒0.4(‒1.3) × 0.3‒0.5(‒0.7) mm, ovate, densely and minutely pubescent outside, glabrous inside, trichomes to 0.1 mm. Male flowers not plate-like at anthesis, yellowish to bright yellow or reddish orange, remarkably scented; pedicel (2.1‒)4‒5.3(‒6.6) mm long, 0.1‒0.2 mm in diameter, slender, minutely and sparingly pubescent, trichomes to 0, 1 mm; sepals (3‒)4(‒5), (1.2‒)1.9‒2.3(‒2.9) × (0.3‒) 1‒1.8 mm, ovate to slightly oblong, obtuse, imbricate, slightly cucullate towards the apex, minutely pubescent outside, trichomes to 0.1 mm, glabrous inside, minutely ciliate, cilia to 0.2 mm; stamens 3, one-whorled, surrounding the disk and hardly enveloped by the marginal lobes of the disk, filaments (0.8‒)1.5‒3.4(‒4.2) mm long, white, anthers (0.4‒)1‒1.1(‒1.4) mm long, 0.5‒1 mm in diameter, ovate-elliptic, subbasifixed to dorsifixed, introrse, yellow, glabrous; disk (0.3‒)0.5‒0.8(‒1.2) mm in diameter, 0.1‒0.4 mm high, concave, cupular, thin, smooth, margin slightly lobed, glabrous, sometimes with a central conical projection to 0.1 mm. Female inflorescence clusters borne axillary on leafless branches (category III), sometimes on main branches (category II), to ca 7 flowers; bracts 0.6‒0.9 × 0.7‒1.2 mm, ovate, densely and minutely pubescent outside, glabrous inside, trichomes to 0.1 mm. Female flowers plate-like at anthesis, with pedicel 1.9‒3.2 mm long, 0.9‒1 mm in diameter, more robust than in male flowers, minutely pubescent, trichomes to 0, 1 mm; sepals 4‒5, 2.9‒3.9 × 2.5‒3.1 mm, ovate, imbricate, cucullate, minutely and sparingly pubescent outside, trichomes to 0.1 mm, glabrous inside, minutely ciliate at margin, cilia to 0.1 mm; disk 2.8‒3.3 mm in diameter, 0.3‒0.4 mm high, cupulate, fleshy, glabrous; style 1, 0.6‒1.1 mm long, not noticeably hollow, 3(‒4)-branched, basally united to 0.3‒0.5 mm; stigmas 3(‒4), each arm 0.8‒1 mm long, stigmatic surface 1‒1.7 mm wide, spatulate to obdeltoid; ovary 1.7‒2.1 mm long, 2.4‒2.7 mm in diameter, globose, apex depressed, 3(‒4)-celled, glabrous. Fruits 19‒20.7(‒30) mm long, 20‒23.4(‒30) mm in diameter, subglobose, apically slightly depressed, surface smooth, uneven, reddish brown when young, then red, glabrous, sepals deciduous, style and stigmas deciduous, 3(‒4)-celled, (1‒)2‒3(‒4)-seeded, seeds ca 16.9 mm long, ca 9.7 mm in diameter; fruiting pedicel 2‒4.6(‒8) mm long, 2.3‒2.5 mm in diameter, glabrous.

Distribution and habitat

Central Africa: Angola ( Cabinda), Cameroon (East Region and South Region), Equatorial Guinea (Centro Sur), Gabon (Estuaire, Ogooué-Ivindo and Ogooué-Lolo) and Republic of the Congo (Lékoumou and Sangha, not mapped) ( Fig. 4 ). Primary and secondary wet evergreen forests, gallery forests; 50‒650 m a.s.l.

Phenology

Flowering specimens were collected from December to August, fruiting specimens from April to December.

Notes

Most gatherings of D. gabonensis available to us were made from male individuals, and we have only been able to study a few fruiting specimens and only two with female flowers. Herbarium labels inform us about many relevant features of the species, apart from those used to elaborate the description, such as the wood, brownish at first, turning white by exposure and soon destroyed by insects, the scarletred extremities of its twigs, and that male flowers are frequented by bees. Female inflorescences of D. gabonensis are mostly axillary on leafless branches (category III), although they are also observed on older wood along branches (which could eventually fall within category II), unlike male ones, which are constantly axillary on leaf or leafless branches (categories III and IV). In addition, the protologue of D. gabonensis stated that male inflorescences were yet “rarely on the older wood” (the position of female ones is not described), without enabling us to know whether this refers merely to the leafless portions of the branchlets immediately under the leaves or also to the older wood of main branches, as seems to be possible for females. Only future field observations can help to describe the exact distribution of the inflorescences located on the branches of both sexes of D. gabonensis .

Despite the superficial resemblances that one might find between specimens of D. gabonensis and the two species treated below, as they all have leaves of similar dimensions with subentire margins ( D. gabonensis ) to shallowly and obscurely crenulate-serrulate (all three species) and glabrous fruits, there are numerous useful diagnostic characters, both vegetative and reproductive, that can be used to separate them (see Table 1 for a summary of diagnostic characters). From D. aphanes sp. nov. and D. cauta sp. nov., we can distinguish D. gabonensis , first of all, because the first two are mostly trunciflorous (category I). Bud scales are larger in D. gabonensis than in D. aphanes and D. cauta and have different shapes, narrowly triangular in D. gabonensis and more or less ovate in the others. Twigs and branchlets are completely glabrous in D. aphanes and D. cauta , while they are glabrescent in D. gabonensis , often with few scattered trichomes to 0.1 mm. The petiole of D. gabonensis is usually longer than those of the other two species ((4.2‒)7.7‒9.6(‒13.1) vs (3.4‒)5.8‒8.1(‒8.6) mm) and its surface is different, smooth and coarsely wrinkled and appearing blistered on dried mature material of D. gabonensis , while the petioles of D. aphanes and D. cauta are finely and densely wrinkled. The leaves of D. gabonensis are distinctively glossy above and frequently cuspidate, as well as they frequently have markedly asymmetrical bases, while D. aphanes and D. cauta are much more lusterless above and, although they are also acuminate, the apex diminishes much more smoothly and the base is oblique.

Apart from the different placement of inflorescences, the comparatively small and reduced male flower of D. gabonensis is quite different from those of D. aphanes sp. nov. and D. cauta sp. nov.: fewer sepals (usually 4, vs 5) and stamens (3, vs 11‒17), and a much smaller disk ((0.3‒)0.5‒0.8(‒1.2) vs 3.1‒4.6 mm in diameter). The male disk of D. gabonensis is concave and more or less thin, often with a central conical projection, while in the other two species it is convex and more developed. Other diagnostic characters are the slender pedicels of the male flowers of D. gabonensis (in the other two species they are much more robust and usually shorter) and the indumentum of the sepals because that of D. gabonensis is sparingly and minutely pubescent, while those of D. aphanes and D. cauta are glabrous (with the exception of short marginal cilia). Finally, a somewhat longer and branched style and spathulate to obdeltoid stigmas are also useful to distinguish D. gabonensis from the other two species, which have much shorter, not branched, styles and consistently obdeltoid stigmas.

The characters linked to flowers and inflorescences of D. gabonensis , as well as its large 3(‒4)-celled fruits, may make its classification within D. sect. Oligandrae problematic in our opinion (most of the representatives of this section bear different-sex flowers of similar appearance (that is, not dimorphic) and small, 2-celled fruits). However, for the moment we leave D. gabonensis classified within its traditional section until the typification and amendment of the sections of the genus will be carried out in the near future in conjunction with molecular phylogenies.

Nomenclature

We choose as lectotype of D. gabonensis the specimen P04707398 of the gathering Klaine 1278, since we consider it to be the most suitable specimen located among the syntypes cited in the protologue: “Lower Guinea. Gaboon: Libreville, Klaine, 551! 690! 1034! 1278! 3188!” ( Hutchinson 1912). Hutchinson described D. gabonensis on the basis of several gatherings made by T.J. Klaine in the surroundings of Libreville ( Gabon) between the years 1896 and 1902, as well as on an unnumbered illustration with analysis drawn by E. Delpy in 1908 ( Fig. 2 , modified) and based on a part of these gatherings. This illustration belongs to the Tabulae herbarii L. Pierre (Delpy 18??‒19??) opera utique rej., a suppressed work ( Rijckevorsel 2011; Turland et al. 2018, Appendix I) and, consequently, the designation “ Cyclostemon gabonense Pierre ” that appears on it (and also cited in the protologue of D. gabonensis ) was not validly published.

The gathering Mildbraed 7672 was cited by Pax & Hoffmann (1922) as a part of the original material associated to D. calvescens Pax & K.Hoffm. , a different species that also inhabits Central Africa, but it is actually conspecific with D. gabonensis ( Quintanar et al. 2022) and we have therefore classified it here as such (see below the list of studied specimens).

IUCN Red List preliminary status

The species is known from 30 gatherings made between 1896 (Klaine 551) and 2021 (transects made by MBG team). The geographical information for Ledreau 55 is imprecise and is therefore not considered for this evaluation. We consider two occurrences as extirpated because of the loss of forest cover due to urbanization at the surroundings of Libreville (Klaine 182, 437, 551, 690, 1034, 1034bis, 1278) in Gabon and Bertoua (Breteler 829) in Cameroon. The 29 remaining gatherings represent 13 occurrences representing 8‒9 subpopulations. The extent of occurrence (EOO) of D. gabonensis is estimated to be 162 814 km 2, exceeding the upper threshold for ‘Vulnerable’ status under subcriterion B1, whereas its area of occupancy (AOO) is estimated to be 52 km 2, which falls within the limits for ‘Endangered’ status under the subcriterion B2. In Cameroon, the two occurrences are threatened by wood harvesting (two locations). The occurrence from Equatorial Guinea is located within a protected area (Monte Alén National Park). In Gabon, one occurrence is located within a protected area (Forêt des Abeilles); four occurrences are located within two different logging concessions, and are threatened by logging (two locations); the other two are threatened by shifting agriculture and wood harvesting (two locations). In the Republic of the Congo, the occurrence is located within a logging concession and threatened by logging (one location). In Cabinda ( Angola), the three occurrences are threatened by shifting agriculture and wood harvesting (three locations). All activities induce a decline in the quality and extent of the habitat of this species. As a consequence, these 13 occurrences represent 10 locations (cf. IUCN Standards and Petitions Committee 2022), with regard to the most serious plausible threat (urbanization), within the limits for ‘Vulnerable’ status. We infer a past, current, and future continuous decline in the extent of occurrence, area of occupancy, number of locations, and number of mature individuals. Drypetes gabonensis is therefore assigned a preliminary status of ‘Vulnerable’ [VU B2ab(i,ii,iii,iv,v)].

Figures

Fig. 2. Drypetesgabonensis Pierre ex Hutch. a. Branch, leaves, male inflorescences. b. Branch, leaves, female inflorescences. c. Male flower before anthesis. d. Male flower. e–f. Sepals of male flower. g. Longitudinal section of male flower. h. Male flower without sepals. i. Ventral view of anther. j. Disk of male flower. k. Longitudinal section of the disk of the male flower, showing the central conical projection. l. Female flower without a sepal. m. Opened ovary showing the ovules and transverse section of the ovary. n. Fruit. o. Opened fruit showing the seeds. p. Seed. [a–p, Klaine 551, 690, 1034, 1278 (many specimens, see list of studied material).] Details c–h share the scale of 3 mm placed in d. Details j and k share the scale of 2 mm placed in j. details l and m the scale of 3 mm placed in m. Illustration by E. Delpy, modified for its publication in Flore du Gabon (Harris et al. 2021).

Fig. 4. Distribution of Drypetes gabonensis Pierre ex Hutch. (blue circles), Drypetes aphanes Quintanar, D.J.Harris & Barberá sp. nov. (red triangles) and D.cauta D.J.Harris, Barberá & Quintanar sp. nov. (green squares).