Monotes hypoleucus (Oliv.) Gilg var. caloneurus (Gilg) Meerts, 2017

Meerts, Pierre, Rougelot, Quentin & Sosef, Marc, 2017, Revision of the genus Monotes (Dipterocarpaceae) in D. R. Congo, with implications for Angola and its distinction from Marquesia, Phytotaxa 308 (2), pp. 151-205 : 186-188

9c. Monotes hypoleucus (Oliv.) Gilg var. caloneurus (Gilg) Meerts , comb. et stat. nov.

Basionym: Monotes caloneurus Gilg (1899: 136 , excl. Schweinfurth 2678 (B†, K!)); Bancroft (1937: 137; 1939a: 360); Catarino et al. (2013: 267); De Wildeman (1927: 170); Duvigneaud (1949: 44); Figueiredo & Smith (2008: 67); Lebrun & Stork (1991: 144).

Lectotype (designated here): — ANGOLA. Malange , March 1880, Mechow 455 (lecto-: W! [barcode W1889-0054616]; isolecto-: B†, photo: BM!, K!).

= Monotes elegans Gilg (1908b: 291) ; Bancroft (1939a: 340, 376, 379); Catarino et al. (2013: 268); De Wildeman (1927: 172): Duvigneaud (1949: 47; 1961: 419); Engler (1921: 522); Figueiredo & Smith (2008: 67); Lebrun & Stork (1991: 144); Verdcourt (1989: 9); White (1962: 262). Type:— TANZANIA, bei Tabora, between Rubugwa and Mkigwa, miombowald, Holtz 1474 (holo-: B†; BRLU! (photo of holotype )), syn. nov.

= Monotes dawei Bancroft (1936a: 43) ; Bancroft (1937: 141; 1939a: 354); Catarino et al. (2013: 268); Figueiredo & Smith (2008: 67). Lectotype, designated here:— ANGOLA, Bié, Libolo, Longa river, Dec. 1921, Dawe 324 (lecto-: K!). ≡ Monotes caloneurus var. dawei (H.H.Bancr.) Duvigneaud (1949: 44) ; Lebrun & Stork (1991: 144), syn. nov.

= Monotes schmitzii Duvigneaud (1949: 51) ; Lebrun & Stork (1991: 144). Lectotype (designated here):—D.R. CONGO. Upper Katanga, Mukuen [incorrectly spelled “Metuen” in the protologue], 10 km SSW Elisabethville, sommet de la pente sud, sol superficiel, nombreux blocs rocheux, 15 April 1947, Schmitz 469 (lecto-: BR! [barcode BR000005847105], isolecto-: BRLU!, YBI!), syn. nov.

Diagnosis:— Differs from the type variety by the following traits: indumentum of lower surface of the leaf thinner and/ or sparser, with cottony or curly hairs, mostly <0.8 mm, generally not completely hiding reticulum, or, when hiding reticulum, upper surface persistently tomentellous with stellate hairs.

Tree up to 15(–20) m high; branchlets tomentellous, becoming glabrous. Leaf: petiole 6–20 mm long, rather slender; leaf blade elliptic to ovate-elliptic or obovate-elliptic, (6–)7–14(–18) × 3–8.5 cm, obtuse, rounded to slightly cordate at the base, rounded to slightly emarginate at the apex; upper surface smooth, sparsely to densely puberulent or tomentellous, more or less glabrescent; hairs very short, not exceeding 0.15(–0.25) mm (often much shorter) and not discernible by touch, only visible with a microscope, simple, fasciculate, or stellate, variable in shape, never straight, irregularly curled, always mixed with yellow glands; lower surface discolorous, greyish, beige or whitish, with reticulum either conspicuous (hairs sparse) to inconspicuous (covered by indumentum); hairs variable in length and density, with relatively short curled to cottony hairs on the nerves and reticulation, with the lumen occupying ca. half of the diameter (ca. 8 μm), and with the interreticular areoles densely covered with minute stellate hairs; at least some hairs> 0.3 mm long; midrib prominent beneath; lateral nerves in 12–16 pairs (with a strong tendency to the formation of short subsidiaries) curving towards the apex just before and without reaching the margin of the leaf; veins conspicuous;. Inflorescences up to 8 cm long and 4 cm wide, axillary, pedunculate, relatively lax, many-flowered, greyish- or fulvous-tomentose; pedicels 2–3 mm long. Flower: sepals 3 mm long, with a dense cottony tomentum; petals 10 mm long, densely rufous-sericeous-tomentose; stamens with anthers produced into a rounded appendage. Fruit 10–15 mm in diameter, subglobose, rounded or slightly subconical at the apex; wings reddish or brownish, very variable in shape, suborbicular (2.5– 2 cm in diameter) to linear (5.5 × 0.8 cm).

Illustrations: — Figs. 3N , 4M , 5F,G , 12A–G .

Distribution in D.R. Congo: —Lacs Edouard et Kivu, Upper Katanga, widespread.

Distribution elsewhere: — Angola, Burundi, Tanzania, Zambia; widely distributed in the north of the Zambezian Region.

Habitat and ecology: —Miombo woodlands on various types of soil, often on hill tops, on rocky soil; Brachystegieto-Monotetum katangense, sous-association à Brachystegia utilis ( Schmitz 1971) , degraded shrubby savannah on sandy soil.

Vernacular names: —Kansimba (Kiholoholo), kassumba (Kibemba), kimpampa (Kibemba), mumpunge (Kihololo), muyembe (Kiluba).

Uses: —Host of the edible caterpillar of the cavorting emperor moth, Usta terpsichore ( Saturniidae ) ( Malaisse 1997); fire wood (N of Kalemie).

Other representative specimens examined:— ANGOLA. Malange, January 1880, Mechow 434 (B†, M!, W!). — D.R. CONGO. Lacs Edouard et Kivu: Réserve forestière Colonie, Musingiro, April 1944, Michelson 601 (BR!).

Lower Katanga: Kaniama, savane claire, March 1938, Herman 2222 (BR!). Upper Katanga: Route Baudouinville- Kapona, sol sablonneux, 17 July 1957, Devred 3480 (BR!); Plateau des Biano, 32 km N de Tenke, bosquet à Uapaca- Philippia sur sable, 3 August 1948, Duvigneaud 1318M2 (BRLU!); S de Biano-gare, vallon, pente sableuse, forêt claire à Brachystegia-Monotes, 6 August 1948, Duvigneaud 1350M (BRLU!); Entre Mukumbi et Swambo, 13 km E of Swambo, forêt claire à Brachystegia spiciformis sur plateau, terre rouge profonde, Duvigneaud & Timperman 2109 (BRLU!); Mindingi, colline dominant la route, broussailles arbustives, 1 August 1956, Duvigneaud & Timperman 2190M (BRLU!); Mukumbi, brousse très arbustive de dégradation de la forêt claire sur sol sableux gris-rose, 3 August 1956, Duvigneaud & Timperman 2195 (BRLU!); Kisenge, route de Divuma, forêt claire à Marquesia , et Isoberlinia sur terre grise compacte, 19 August 1956, Duvigneaud & Timperman 2371 (BRLU!); Mitonte, forêt claire sur terre rouge, 3 May 1957, Duvigneaud 3006 Mo (BRLU!); Tantara, forêt à Brachystegia microphylla sur colline rocheuse, 14 May 1957, Duvigneaud 3203 (BRLU!); entre Mukumbi et Swambo, forêt claire sur terre ocre compacte, 1 June 1957, Duvigneaud 3338M1A (BRLU!); Entre Swambo et Mukuni, forêt claire à Brachystegia floribunda sur terre rouge, 1957, Duvigneaud 3345M4 (BRLU!); Musoshi, forêt claire à Marquesia macroura , 6 June 1957, Duvigneaud 3424 (BRLU!); Entre Jadotville (Likasi) et Kambove, forêt claire sur terre rouge, June 1957, Duvigneaud 3560Mo (BRLU!); Mitwaba, verger à Dipterocarpaceae sur sol de plateau, 17 January 1960, Duvigneaud 5095M (BRLU!); 10 km S of Mitwaba, bosquet de pente à Uapaca , 17 January 1960, Duvigneaud 5096M (BRLU!) (“typical M. caloneurus ” fide Duvigneaud in schedis); 12 km NW of Elisabethville (Lubumbashi), parcelle expérimentale de forêt claire sur sol ocre profond sur dolomie, Gathy 93 (BRLU!); Mukuen, January 1948, Schmitz 1332 (para-: BR!).

Discussion:— Var. caloneurus is the least well-defined entity within M. hypoleucus . It comprises a group of forms, extremely variable in density and persistence of the indumentum on the upper surface, distribution and thickness of the indumentum on the lower surface and leaf size. Variation of most of these traits is continuous. Even though some combinations of traits seem more frequent than others, we have not been able to find any reliable diagnostic trait to separate M. elegans , M. caloneurus and M. schmitzii .

The typification of Monotes caloneurus Gilg is problematic. Of the six specimens cited in the protologue, Schweinfurth 2678, originating form the Sudanian region belongs in M. kerstingii Gilg as already pointed out by Hutchinson & Dalziel (1927) and Bancroft (1939a). Both Büchner 159 and Büchner 524 have been lost in Berlin and no duplicates apparently exist. Mechow 434 (W!, M!) and Mechow 455 (W!) are the only syntype specimens remaining from Angola. Mechow 434 deviates from the usual description of the taxon in having areoles mostly glabrous and indumentum restricted to the reticulum and hence, being very weakly discolorous. Mechow 455 does show the pubescent areoles and is therefore here chosen as the lectotype.

The protologue of M. schmitzii cites two syntypes, collected from the same tree at two dates (Schmitz 469, with fruits; Schmitz 1332, with flowers). Schmitz 469 is here chosen as the lectotype, because it has more extensive collecting information on the label.

Soon after its description, Monotes dawei was already recognized by Bancroft herself (1939a: 354) “…to be the least distinct member of the caloneurus group of forms…” and to represent “…a somewhat extreme, narrow-leaved form of M. caloneurus itself.”. Such forms are certainly not endemic of Angola ( Duvigneaud 1949: 45) (e.g. Luxen 151 (BR!) and Luxen 152 (BR!, P!), both from Lower Katanga near Kalemie, and belong in the phenetic variation space of M. hypoleucus var. caloneurus .

The limits between var. caloneurus and var. hypoleucus are blurred by intermediate specimens (e.g. Desenfans s.n. (BRLU!), Desenfans 5707 (BRLU!), Duvigneaud 3676 (BRLU!), Herman 2222 (BR!)). Although there is great overlap in leaf size between var. angolensis and var. caloneurus , the largest-leaved morphs of var. angolensis tend to have a glabrous upper surface of the leaf while the smallest-leaved forms of var. caloneurus generally have a densely tomentellose upper surface.

Figures

FIGURE 3 A–H. Details of lower surface of the leaf.A. Monotes adenophyllus var. adenophyllus (Duvigneaud 5112). B. M. adenophyllus var.homblei (Duvigneaud 4601). C. M.africanus (Duvigneaud 2006). D.M.autennei (Duvigneaud 5260). E.M.dasyanthus var.dasyanthus (Duvigneaud & Timperman 2341). F. M.dasyanthus var. heterotrichus (Duvigneaud 1141). G. M. dasyanthus var. mutetetwa (Duvigneaud 950). H. M. doryphorus (Duvigneaud 5267).

FIGURE 4 A–H. Details of upper surface of the leaf.A. Monotes adenophyllus var.adenophyllus (Duvigneaud 5044). B. M.adenophyllus var.homblei (Duvigneaud 4570). C. M.africanus(Duvigneaud 2006). D. M.autennei(Plancke 111/1532). E.M.dasyanthus var.dasyanthus (Duvigneaud & Timperman 2341). F. M. dasyanthus var. heterotrichus (Duvigneaud 4493). G. M. dasyanthus var.mutetetwa (Duvigneaud 950). H. M. doryphorus (Duvigneaud 5267).

FIGURE 5 A–H. SEM photographs of leaf blade surfaces for 12 members of Monotes. A. M. adenophyllus var. adenophyllus, lower surface (Delevoy 524, type of M. delevoyi). B. M. autennei, lower surface (Duvigneaud 3267 (type of M. autennei)). C. M. autennei, upper surface (Duvigneaud 3267). D. M. hypoleucus var. angolensis, lower surface (Duvigneaud 950M2, type of M. oxyphyllinus). E. M. hypoleucus var. angolensis, upper surface (Duvigneaud 950M2). F.M. hypoleucus var. caloneurus, lower surface (Schmitz 1332 (type of M. schmitzii)). G. M. hypoleucus var. caloneurus, upper surface (Schmitz 1332 (type of M. schmitzii)). H. M. hypoleucus var. hypoleucus, lower surface (Welwitsch 1036 (type of M. hypoleucus)).

FIGURE 12. Colour photographs of leaves: Monotes hypoleucus var. caloneurus. A. Duvigneaud 4764, B. Duvigneaud 4850, C. Duvigneaud 3203, D. Duvigneaud 3338, E. Duvigneaud 2123, F. Duvigneaud 5095, G. Duvigneaud & Timpeman 2109. Scale bar = 5 cm.