Xylopia wilwerthii De Wildeman & T. Durand, Ann. Mus. Congo, Ser . 2, Bot. 1(1): 5. 1899.

Johnson, David M. & Murray, Nancy A., 2018, A revision of Xylopia L. (Annonaceae): the species of Tropical Africa, PhytoKeys 97, pp. 1-252 : 116-121

25. Xylopia wilwerthii De Wildeman & T. Durand, Ann. Mus. Congo, Ser. 2, Bot. 1(1): 5. 1899. Fig. 31

Xylopia wilwerthii var. cuneata De Wildeman in De Wildeman & T. Durand, Bull. Soc. Roy. Bot. Belg. 40(2): 63. 1901. Type. DEMOCRATIC REPUBLIC OF THE CONGO ["Congo Belge"]. Kinshasa Province, Kimuenza, May 1901, J. Gillet s. n. (holotype: BR!; isotype: BR! [0000008825476]).

Type.

DEMOCRATIC REPUBLIC OF THE CONGO [" Congo Belge"]. Mongala Province , Rég. III, Upoto, 1896, Capt. Wilwerth s. n. (holotype: BR!, isotype: BM! [000511002]) .

Description.

Tree up to 15 m tall, d.b.h. up to 10 cm, slender with a short-branched crown. Twigs brown, eventually brownish gray to gray, fine-pubescent, the hairs 0.1-0.2 mm long, soon glabrate; nodes occasionally with two axillary branches. Leaf with larger blades 5.1-8.9 cm long, 1.5-2.8 cm wide, chartaceous, concolorous, elliptic to elliptic-oblong, apex acuminate to caudate, the acumen 5.5-16 mm long and rounded at the tip, base cuneate and somewhat decurrent on petiole; glabrous adaxially, sparsely pubescent to glabrate, occasionally with longer seta-like hairs along midrib abaxially; midrib plane or impressed adaxially, raised abaxially, secondary veins indistinctly brochidodromous and more or less parallel, 15-22 per side, diverging at 60-80° from the midrib, these and higher-order veins slightly raised or indistinct on both surfaces; petiole 1.5-3.5 mm long, shallowly canaliculate, sparsely pubescent to glabrate. Inflorescences axillary, 1-flowered, sparsely pubescent; pedicel not pedunculate, 8.5-21.5 mm long, 0.8-1.0 mm thick, articulated at midpoint, sometimes slightly thickened just proximal to lower bract; bracts 2, the upper attached just a few mm proximal to the sepals, the lower just distal to the pedicel midpoint, more or less persistent, 0.8-1.8 (-2.6) mm long, ovate to semicircular, apex rounded or emarginate, ciliate on margins; buds linear-lanceolate, apex obtuse, slightly falciform. Sepals slightly spreading at anthesis, 1/2-2/3-connate, 2.1-3 mm long, 2.8-3.1 mm wide, coriaceous, broadly ovate, apex acute to mucronate, sparsely pubescent. Petals white, cream-colored, or yellow in vivo; outer petals spreading at anthesis, 19-31 mm long, 3.0-3.5 mm wide at base, 1.9-3.0 mm wide at midpoint, chartaceous, ligulate, apex obtuse, densely puberulent adaxially, sparsely pubescent except for glabrous patch at base abaxially; inner petals probably spreading at anthesis, 14.1-24.0 mm long, 2.0-3.1 mm wide at base, 1.4-1.6 mm wide at midpoint, chartaceous, linear, apex acute, base with undifferentiated margin, puberulent on both surfaces except for the glabrous base. Stamens 100-120; fertile stamens 1.1-1.5 mm long, narrowly oblong, apex of connective 0.1-0.3 mm long, shieldlike, overhanging the anther thecae, finely papillate, anthers 12-13-locellate, filament ca. 0.2 mm long; outer staminodes 1.1-1.6 mm long, oblong, apex obtuse, truncate, or emarginate; inner staminodes 1.0-1.1 mm long, oblong to quadrate, apex truncate; staminal cone 2-2.1 mm in diameter, 0.6-0.9 mm high, partially to completely concealing the ovaries, rim laciniate. Carpels 6-13; ovaries 0.8-0.9 mm long, oblong, pubescent, stigmas connivent, 2.9-3.2 mm long, linear, with a tuft of hairs at the apex. Torus flat, 2.5-3.1 mm in diameter. Fruit of up to 12 glabrate monocarps borne on a pedicel 7.5-23.5 mm long, 2-3 mm thick, glabrate; torus 4.5-7 mm in diameter, 3-5 mm high, irregularly depressed-globose. Monocarps with a green exterior and scarlet endocarp in vivo, 1.7 -4.0 cm long, 0.7-1.2 cm wide, 0.5-1.0 cm thick, asymmetrically oblong or ellipsoid, distinctly torulose, apex rounded or with a broad curved beak 1.4-3 mm long, base tapering gradually into a stipe 3-7 mm long, 2.4-4 mm thick, obliquely or longitudinally wrinkled; pericarp 0.4-0.6 mm thick. Seeds up to 6 per monocarp, in a single row, lying parallel or oblique to long axis, 9.6-10.8 mm long, 5.2-7.1 mm wide, 4.9-7.0 mm thick, ellipsoid, elliptic to roughly circular in cross-section, rounded or obliquely truncate at micropylar end, rounded at chalazal end, chestnut brown, smooth, somewhat shining, raphe/antriraphe indistinct, flush with surface of seed, micropylar scar sunken, 1.5-2 mm in diameter, more or less circular; sarcotesta orange in vivo; aril absent.

Phenology.

Specimens with flowers have been collected in March, from May to July, and in September and October, and with fruits from January to March, and in June and October. A ten-year phenology dataset from 1948-1957 from the Luki Reserve in southwestern Democratic Republic of Congo was analyzed by Couralet (2010), who found that X. wilwerthii in the Reserve consistently flowered with the beginning of the rainy season from January to March, with fruit production following shortly thereafter and seed dispersal extending into the dry season from June to September.

Distribution

(Fig. 32 ). Occurs in and near the lower Congo River drainage in the southern Republic of the Congo, western Democratic Republic of Congo, and the Cabinda Province of Angola, where it grows in lowland forest, gallery forest, and forest/savanna edges at elevations of 400-500 m.

Local names.

Bengedele (Donis 2041), bengelele (Devred 3083), nginsa (Pauwels 3478).

Additional specimens examined.

REPUBLIC OF THE CONGO. Foulakari [see below], 21 Sep 1964 (fl), Bouquet 497 (P); région ouest de Brazzaville, chutes de la Fulakari [04°34'58"S, 14°58'27"E], 11 Jun 1960 (fl), Descoings 5852 (P); bord au Congo - Brazzaville, May 1950 (fl), Koechlin 1112 (P); près de Boko (M. Congo), 8 Jan 1956 (fr), Trochain 9603 [6451?] (P) . DEMOCRATIC REPUBLIC OF THE CONGO. Kinshasa: Bas-Congo, Kinshasa, Kimuenza, plateau des restents, Luvanium [4.45917°S, 15.288889°E], 28 Mar 1966 (fl, fr), Breyne 96 (MO); Lovanium, plateau of the residence, 400 m, 31 Jul 1965 (fl, fr), Carrington 7 (K); Univ. Lovanium, Léopoldville camp Livulu, 26 June 1961 (fl), Evrard 6317 (MO); Prov. Leopoldville, Territ. Kasangulu, Keimrwenza-Lobanium, plateau near the guest house, 500 m, 29 Jul 1957 (fl), Robyns 4394 (K).- Kongo Central: Luki, Lukula, Parc forestier de la Nkula, 31 June 1978 (buds), Breyne 3348 (MO); Prov. Leopoldville, Zundu, Mbanza-Ngungu [Territ. Thysville], 14 Mar 1960 (fr), Coupère 1675 (K); I. N. E. A. C. Luki, 3 Feb 1947 (fr), Devred 3083 (BR, P); Kiobo, 22 Sep 1945 (fr), Donis 368 (K); Luki, 11 Oct 1948 (fl), Donis 2041 (BR, K, P); Prov. Léopoldville, Terr. Boma, Luki, parc de la n’Kula, Oct 1948 (fr), Maudoux 72 (K, WAG); Bas-Congo, Luki, INEAC, 1957 (fr), Mahieu 53 (BR); Bas-Congo, Luki, 1959, Mahieu 295 (BR).- Kwango: Terr. Popokabaka, Bombo Makuka, 26 Jun 1959 (st), Pauwels 3478 (BR); Luki, 13 Jan 1947 (fr), Toussaint 2114 (K).- Maï-Ndombe: Taketa, terr. Oshwe, 3°15'S, 19°06'E, 21 Jul 1962 (fl), Jans 1110 (BR) . ANGOLA. In dense woods E of residence of Bungo Mungo, Mayumbe , 11 Jan 1916 (fr), Gossweiler 6169 (BM) .

The long pedicel of Xylopia wilwerthii is unique among African species and unusual within the genus worldwide. This, along with the glabrous caudate leaves, reliably distinguish the species. An unusual aspect of its floral development is that elongation of the axillary pedicel seems to precede elongation of the terminal shoot from which it arises. The orange sarcotesta of its seeds suggest its placement within the X. odoratissima group, but it is isolated there.

Xylopia wilwerthii var. cuneata was distinguished by the leaves being more narrowly cuneate at the bases than in the type specimen of the nominate variety, but we have now seen specimens where this range of variation in the leaf base is encompassed by a single specimen, and the two specimens do not show any other differences, so we do not distinguish them taxonomically. More perplexing is the variation in size and shape of the monocarps; monocarps with larger numbers of seeds are more slender and torulose than those with only 1-3 seeds, which tend to be wider and less strongly constricted between the seeds.

Xylopia wilwerthii and X. flamignii have similar leaves and overlap in distribution, and are thus likely to be confused, especially in the fruiting condition. Xylopia flamignii differs in having a denser persistent indument of the young twigs, a prominent raised reticulum formed by the higher-order veins on the adaxial leaf surface, a distinctly pubescent lower leaf surface, leaves with 13-17 secondary veins per side, up to 22 monocarps per fruit, and seeds only 7-7.6 mm long. Xylopia flamignii is also a larger tree, of up to 30 m in height, reaching canopy or subcanopy level. In contrast, X. wilwerthii is an understory tree with finely pubescent and soon glabrate twigs, indistinct higher-order veins on the adaxial leaf surface, leaves with 15-22 secondary veins per side, never more than 12 monocarps per fruit, and seeds 9.6-10.8 mm long.

Couralet (2010) reported X. wilwerthii , along with Aidia ochroleuca and Corynanthe paniculata , to be a dominant understory species in the Luki Reserve forests, which were characterized as tropical semi-evergreen forest with Prioria balsamifera and Terminalia superba as important canopy species. Forest of Marquesia acuminata was mentioned as the habitat at another site. We calculated a relatively large EOO for X. wilwerthii of 179,602 km 2, coupled with an AOO of only 52 km 2. The size of the EOO is largely due to the great distance of the type locality, Upoto in the Democratic Republic of the Congo, from the remainder of localities where the plant has been collected.

Xylopia acutiflora group

Plants of this group vary in habit from shrubs to canopy-sized trees or rarely lianas. The leaves of several species, for example X. cupularis , X. hypolampra , and X. villosa , have a fine shiny appressed indument abaxially, a character not seen elsewhere among African species. The inflorescences may consist of a single flower, as in X. acutiflora , or, in the case of X. paniculata , up to 32 flowers, and pedunculate inflorescences are common. Monocarps of many species have a thick woody or leathery pericarp and seeds lying in two rows and oriented more or less perpendicular to the long axis of the monocarp. The sarcotesta of most species in this group is pale green, gray, or blue; X. phloiodora has an orange sarcotesta, and sarcotesta color is unknown for X. acutiflora , X. calva , X. dinklagei , X. elliotii , and X. talbotii . Four species within the X. acutiflora group were included in the molecular phylogenetic analysis of the genus by Stull et al. (2017), and all fell within a strongly supported clade along with several Madagascar species. In Africa this species group has a Guineo-Congolian distribution, reaching its eastern limits in South Sudan, western Tanzania, and central Angola.

Three subgroups within the X. acutiflora group are worth noting, all represented in the Stull et al. (2017) molecular study. The first subgroup comprises X. acutiflora , X. dinklagei , X. mildbraedii , X. monticola , X. piratae , X. talbotii , X. thomsonii , and X. unguiculata , most of them segregates of the former X. acutiflora s. l., These are shrubs, sometimes lianescent, or small trees with single-flowered inflorescences borne on short bract-covered pedicels. A second subgroup includes the common and widespread West and Central African riparian species X. longipetala , formerly known as X. parviflora , and X. katangensis . The third subgroup comprises species with large woody monocarps that often split into three segments upon dehiscence: X. hypolampra , X. letestui , X. paniculata , X. phloiodora , X. tanganyikensis , X. villosa , and probably X. calva . Species with a smaller fruit, which may be associated with this final subgroup, include X. cupularis , X. elliotii , and X. pynaertii .

Figures

Figure 31. Xylopia wilwerthii A Habit with nearly mature flower bud B Habit, with open flower C Fruit, side view D Seed, view of micropylar end E Seed, side view F Fertile stamen, abaxial view G Staminode, abaxial view H Flower with petals and some stamens removed, side view I Longitudinal section of flower, with petals removed, showing ovaries surrounded by staminal cone J Inner petal, adaxial view K Outer petal, adaxial view. A, C from Carrington 7 (K) B, F-K from Donis 2041 (BR) D, E from Trochain 9603 (P).

Figure 32. Distribution of Xylopia wilwerthii. Bolder lines represent country borders, fainter lines lakes and major rivers.