Microtropis cerocarpa Savinov & Nuraliev, 2019

Savinov, Ivan A., Nuraliev, Maxim S., Kuznetsov, Andrey N., Kuznetsova, Svetlana P., Luu, Hong Truong, Tran, Huu Dang & Luong, Huu Thanh, 2019, Microtropis cerocarpa (Celastraceae), a new species from southern Vietnam, Phytotaxa 387 (2), pp. 140-148 : 141-146

Microtropis cerocarpa Savinov & Nuraliev , sp. nov. ( Fig. 1 , 2 ).

Microtropis cerocarpa is placed into sect. Microtropis on the basis of its dense inflorescences with sessile flowers. It differs from all other species of this section in the following combination of morphological traits: large thick leaves 23.5–39 cm long and 13–22 cm wide with very short petiole (subsessile) and cordate base, fruit with short rostrum of 1–2 mm long at apex, and immature fruit surface with a pronounced white wax coating in the form of granules.

Type: — VIETNAM. Dak Lak province: Lak district, Bong Krang municipality, Chu Yang Sin National Park, 14 km S of Krong Kmar village, in mixed forest, in ravine, not far from stream, N 12°22’41’’ E 108°21’11’’, 1640 m a.s.l., 03 April 2012, M. S. Nuraliev 466 (holotype MW: MW 0754576, fruiting).

Small tree, glabrous throughout. Stem erect, branched; branches terete, ca. 6 mm in diam. Bark greenish-brownish, with large orange lenticels. Leaves opposite, with very short petiole (subsessile), leaf blade thick, coriaceous, ovate, 23.5–39 cm long and 13–22 cm wide, with 10–12 pairs of secondary veins, apex slightly pointed (acute or shortly acuminate), base cordate, margin entire, leaf surface adaxially dark green and glossy, abaxially light green. Midrib prominent on both surfaces especially abaxially; secondary veins impressed adaxially (but prominent in sicco) and clearly prominent abaxially. Leaf scar large, slightly cordate, with single horseshoe-shaped leaf trace. Flowering inflorescence and flower unknown. Fruits cauliflorous, born on mature trunks below leafy zone, in axils of leaves abscised long time ago, probably in dense several-flowered inflorescences, sessile (lacking pedicel). Fruit a capsule, unilocular and one-seeded, immature capsule fusiform, 22 mm long and 7 mm in diam., with persistent calyx of 5 sepals and short pointed (tapering) rostrum at apex 1–2 mm long. Capsule surface (at least when immature) with distinct white wax coating in form of granules (appearing as scales in sicco). Fruiting sepals overlapping, orbiculate, 3 mm long and 3.3 mm wide, margin scarious, fimbriate.

Other specimens seen (paratypes):— VIETNAM. Dak Lak province: Chu Yang Sin National Park, ranger station 3, montane primary forest, N 12°26’42’’ E 108°26’35’’, 985 m a.s.l., 12 July 2018, Tran Huu Dang, Luu Hong Truong, Dinh Quang Diep, Luong Huu Thanh & Dang Hung Phi TRAN-769 ( SGN, sterile), TRAN-770 ( MW, sterile).

Notes:—1) Some species of Microtropis possess inflorescences of unusual type, characterized by shortened axes and thus remarkable for their compact appearance. Inflorescences of these species are described in different ways in the literature (as subsessile, assembled in fascicles or clusters, e.g. Merrill 1942, Tardieu-Blot 1948; Shui & Chen 2002b; Zhang & Funston 2008). Hou (1962, p. 272) suggested to describe this condition as inflorescences “condensed to sessile clusters”. We here prefer to use a classification which reflects not only the inflorescence habit but also its morphological structure. Within this approach, such inflorescence type can be termed as an umbellate to capitate compound dichasium with shortened peduncle ( Savinov 2013). The inflorescence of the new species described here most likely belongs to this type.

2) It is possible that waxy granules on the fruit surface of Microtropis cerocarpa are clearly pronounced only in immature capsules. This feature was not observed in mature capsules of any other species of this genus. On the other hand, the photos of immature fruits of M. obscurinervia (available at www.plantphoto.cn/tu/585287) clearly show the absence of coating of this type.

Etymology: —The specific epithet “ cerocarpa ” means waxy-fruited and reflects the feature which differs the new species from its most similar congeners.

Taxonomic relationships: —The genus Microtropis s.s. is subdivided into three sections on the basis of inflorescence branching patterns and length of inflorescence axes ( Cheng et al. 1999, Zhang & Funston 2008). Section Cymosopaniculatae (Merrill & F.L.Freeman 1940: 304) C.Y.Cheng & T.C.Kao in Cheng et al. (1999: 153) is characterized by thyrses (sensu Endress 2010) with elongated axes which are often described as paniculate-cymose inflorescences ( Merrill & Freeman 1940) or inflorescences generally possessing prolonged rachis (Zhang & Funston 2008). Section Remotiflorae C.Y.Cheng & T.C.Kao in Cheng et al. (1999: 188) is characterized by compound dichasia (described as inflorescences without prolonged rachis by Zhang & Funston 2008), peduncles often more than 1 cm long (though indicated as “generally up to 1 cm ” by Zhang & Funston 2008, p. 482), flowers loosely aggregated, i.e. the inflorescence internodes and pedicels are well developed (conspicuous). Section Microtropis is characterized by dense glomerate (most often head-like) cymes, peduncles mostly less than 1 cm long and the whole cymes often subsessile or sessile, flowers subsessile or sessile. We place M. cerocarpa into sect. Microtropis according to its inflorescence morphology.

Among the species of sect. Microtropis , the new species is most similar to Microtropis wui from Yunnan ( China), M. obscurinervia from Hainan ( China) and M. rhynchocarpa from northern Vietnam, because they share rather similar habit, large thick leaves and fruits with rostrum. The main morphological differences among these four species are summarized in Table 1. Besides, M. cerocarpa resembles M. osmanthoides ( Handel-Mazzetti 1932: 128) Handel-Mazzetti (1933: 189) from China (Guangxi, Guizhou) and Vietnam in its habit, inflorescence and fruit morphology (fascicled capsules with short rostrum), but considerably differs from the latter in leaf shape and size.

Microtropis cerocarpa is morphologically most close to M. wui and differs from the latter mainly by smaller leaves (23.5–39 cm long vs. 36–50 cm long) with less numerous lateral veins (10–12 pairs vs. 12–15 pairs), shape of leaf blade (ovate vs. obovate or rhombic), subsessile leaf (vs. petiole 4–6 mm long), less numerous flowers in inflorescence (several vs. at least 15–20, on the basis of fruiting inflorescences) and by waxy (vs. smooth) fruit surface.

The most significant differences between the new species and M. rhynchocarpa are shape of leaf base (cordate vs. acute), subsessile leaf (vs. petiole 10 mm long) and short rostrum (1–2 mm long vs. 7–8 mm long).

Finally, M. cerocarpa can be distinguished from M. obscurinervia by its larger leaves (23.5–39 cm long vs. 15–18 cm long), leaf blade with 10–12 (vs. 7–11) pairs of lateral veins, very short petiole, i.e. subsessile leaf (vs. petiole 8–15 mm long), immature capsule 22 mm long and 7 mm in diam. (vs. 15–20 mm long and (3–) 4–6 mm in diam.) and fruit surface with a wax coating (vs. smooth).

There are three more species of Microtropis which also possess rostrum at the fruit apex: M. longicarpa Q.W.Lin & Z.X.Zhang (2010: 142) from Yunnan, M. daweishanensis Q.W.Lin & Z.X.Zhang (2010: 143) from Yunnan and M. petelotii Merrill & F.L.Freeman (1940: 291) from Yunnan and northern Vietnam ( Lin & Zhang 2010). All of them show considerable differences from M. cerocarpa with their main distinguishing character being the elongated inflorescence axes including peduncles; all of them thus represent another section, i.e. Microtropis sect. Remotiflorae .

Distribution and habitat:— Microtropis cerocarpa is currently only known from Dak Lak province in southern Vietnam. The map is provided by Nuraliev et al. (2015, Fig. 4, 2017, Fig. 4). The holotype was collected in a small mountain ravine at the elevation 1640 m near a local stream where this species occurs in quite dense population of both reproductive and immature individuals. Microtropis cerocarpa was observed on local mountain slopes above the holotype location. The paratypes were found at a distance of 12 km from the holotype at significantly lower elevation, i.e. 985 m, and plants of this species were also quite numerous there. This suggests that M. cerocarpa is locally common across the Chu Yang Sin mountain range.

Forest inhabited by M. cerocarpa in the area of holotype collection possesses the following characteristics. Trees are up to 20–24 m high, with trunk DBH 40–60 cm and dense crowns 6–10 m in diam. The upper forest stratum is dominated by representatives of the genera Castanopsis and Lithocarpus ( Fagaceae ) and also includes Dacrycarpus imbricatus , Podocarpus neriifolius ( Podocarpaceae ), Magnolia sp. ( Magnoliaceae ), Cinnamomum sp. , Litsea sp. ( Lauraceae ), Exbucklandia populnea , Rhodoleia championii ( Hamamelidaceae ), Altingia sp. ( Altingiaceae ), Carpinus sp. ( Betulaceae ), Calophyllum sp. ( Calophyllaceae ), Syzygium sp. ( Myrtaceae ), Schima wallichii ( Theaceae ) and Anneslea fragrans ( Pentaphylacaceae ). Subordinate strata comprise species from the genera Dillenia ( Dilleniaceae ), Garcinia ( Clusiaceae ), Acer ( Sapindaceae ), Camellia ( Theaceae ), Eurya , Ternstroemia ( Pentaphylacaceae ), Ixora , Lasianthus ( Rubiaceae ), Tabernaemontana ( Apocynaceae ), Clerodendum ( Lamiaceae ), Schefflera ( Araliaceae ), Caryota and Pinanga ( Arecaceae ).

Phenology:—In late March and early April, the plants showed fruits apparently formed quite a long time ago but still immature (with green epidermis) and not dehisced. In mid-July, we were unable to find any reproductive structures despite intensive search.

Conservation status:—Distribution of Microtropis cerocarpa is most likely restricted to Chu Yang Sin mountain range. On the other hand, it is found in rather distant parts of this range at various elevations and represented by numerous individuals. There is thus a possibility that this species is common and abundant in Chu Yang Sin National Park which is a protected area of significant size. For these reasons, special investigations are needed for evaluation of conservation status of this species, which is currently estimated as DD according to IUCN Red List (2018).

Figures

FIGURE 1. Microtropis cerocarpa. A–C. Mature tree, leafy shoots. D. Young plant. E. Trunk with branches. F. Resting buds (possibly, an inflorescence). G. Branch with leaf scar. Nuraliev 466. All photos by M. Nuraliev.

FIGURE 2. Microtropis cerocarpa. A. Branch node with fruiting inflorescences in axils of abscised leaves; the capsule at left is fallen off leaving its calyx. B. Fruiting calyx, top view. C. Fruiting inflorescence with a single capsule developed or left. D. Capsule base with calyx, lateral view. E. Surface of immature capsule; note the wax granules. F. Cross section of immature capsule. Nuraliev 466. All photos by M. Nuraliev.