Monotes rubriglans subsp. upembensis 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 : 194

13a. Monotes rubriglans subsp. upembensis Meerts , subsp. nov.

Type: —D.R. CONGO. Katanga, Upemba, savane boisée entre Kilwesi et rivière Muye, 10 September 1948, de Witte 04232 (holo-: BR!, iso-: BR!).

Diagnosis:— Differs from the typical subspecies by the inflorescence being composed of a long thyrse, or a narrow panicle, 4–11 cm long, much longer than wide, with a few reduced leaves, borne on defoliated twigs below the leaves, the more developed indumentum of the lower surface of the leaf, with either stellate hairs in areoles or simple hairs on veins and reticulum or both, the tomentose twigs and the subsidiary glands in the axils of secondary nerves (not next to the nerves).

Twigs densely tomentose; stipules reddish, ciliate, more or less persistent. Leaf: petiole 11–40 mm long, 2.5–3 mm in diameter, often distally dilated and geniculate, generally densely pubescent; subsidiary red glands present in the axil of secondary nerves, sometimes masked by hairs; upper surface of leaf blade often with reddish tinge on main nerve and/or with red flecks or completely reddish; upper surface with nerves densely pubescent; lower surface of leaf concolorous to discolorous, with the areoles glabrous to densely stellate-pubescent; costa, secondary nerves and reticulum generally with hyaline hairs. Inflorescence: a thyrse or a narrow panicle up to 11 cm long with 1–3 short branches, on previous year’s growth, with one or a few reduced leaves; peduncle 3–8 cm, densely pubescent, striate, pale green; inflorescence leaves elliptic, ca. 25 × 10 mm, with a conspicuous mucro, greyish-green, with soon caducous minuscule lepidote-stellate hairs intermingled with long straight simple hairs; floral bracts reddish, ciliate, generally persistent. Flower: pedicel 1–2 mm long, sepals broadly ovate-elliptic 3–5 × 2–4 mm, petals 8–12 × 3.5–5 mm, whitish with a reddish tinge within, stamens 5–8 mm long. Fruit ovoid, ca. 10 × 7 mm, with a conical apex; wings obovate, 2.0–4.0 × 0.8–1.5 cm, pale reddish.

Variation:— The Katangan collections are extremely variable for many traits, including extent and density of indumentum, leaf colour and shape and petiole length. Leaf shape ranges from ovate to elliptic or obovate, with the leaf apex ranging from deeply emarginate to bluntly acuminate. Significantly, the type specimen of Monotes rubriglans shows similar variation in leaf shape within the same collection and even on the same twig. Although the Katangan material is obviously heterogeneous, variation is very difficult to translate into a coherent classification system. We propose to recognize two varieties.