Disanthus ovatifolius, 2017

Averyanov, Leonid V., Endress, Peter K., Quang, Bui Hong, Nguyen, Khang Sinh & Nguyen, Dzu Van, 2017, Disanthus ovatifolius (Hamamelidaceae), a new species from northwestern Vietnam, Phytotaxa 308 (1), pp. 104-110 : 105-108

D. ovatifolius Averyanov, P.K. Endress, B.H. Quang & K.S. Nguyen , sp. nov. ( Fig. 1 & 2 ).

Diagnosis:— Small evergreen hermaphrodite tree; young shoots densely hairy, later glabrous; buds perulate, purple; stipules present, paired, caducous; leaves alternate, petiolate; simple, leathery, with 3 palmate veins and pinnate venation; inflorescence bracteate, capitate, axillary, (1)2–3-flowered; floral bracts sub-verticillate; flowers red, sessile, actinomorphic, bisexual, 5-merous, with 2- whorled perianth; floral cup inside densely hairy, outside glabrous; sepals ovate, recurved glabrous, ciliate; petals ribbon-like, spreading; stamens 5, filamentous, with no connective protrusion; anthers dorsifixed, extrorse, tetra-sporangiate; gynoecium, of 2 hemi-syncarpous carpels; ovary semi-inferior, 2-locular, styles 2, cylindrical, with truncate stigma; fruit semi-woody, sessile, hemi-syncarpous 2-carpellate capsule, enveloped by woody floral cup fused to each other forming compact infructescence of 2–3 capsules, dehiscing septicidally by 2 valves, fruiting carpels cornute at apex; seeds (6)8(10) per carpel, ejected, glossy black.

Type: — VIETNAM, Lao Cai province, Bat Xat district, Y Ty commune, Nhiu Co San Mountain , primary evergreen broad-leaved humid forest on sandstone at elevation about 1858 m a.s.l. around point 22°37’27.5N 103°37’23.6E, small tree, to 5 m tall, locally common, 21 March 2016, N. V. Du, B. H. Quang, T. D. Binh, D. Justice, B. White, A. Hill, S. McMahan, D. Hinkley, HN-UBC-68 (holotype, HN; isotypes, HN) .

Paratypes:— VIETNAM, Lao Cai province, Bat Xat district, Y Ty commune,Nhiu Co San Mountains, primary evergreen broad-leaved humid forest on sandstone at elevation about 1861 m a.s.l. around point 22°37’30.2N 103°37’28.2E, small tree about 5 m tall, locally common, 25 October 2016, R. Baines, A. Luke, A. Summers, W. Ritchie, Q. B. Hong, D. V. Nguyen, K. S. Nguyen, HN-E-304 ( HN, LE). VIETNAM, Lao Cai province, Bat Xat district, Y Ty commune, Nhiu Co San Mountains, primary evergreen broad-leaved and mixed forest with Tsuga dumosa on sandstone at elevation about 2367 m a.s.l. around point 22°35’46.9N 103°37’31.8E, small tree about 4 m tall, not common, 26 October 2016, R. Baines, A. Luke, A. Summers, W. Ritchie, Q. B. Hong, D. V. Nguyen, K. S. Nguyen, HN-E-381 ( HN, LE). VIETNAM, Lao Cai province, Bat Xat district, Y Ty commune, Nhiu Co San Mountains, primary evergreen broad-leaved humid forest on sandstone at elevation 1860 m a.s.l. around point 22°37’34.2N 103°37’32.9E, small tree, up to 5 m tall, locally common, 2 November 2016, B. H. Quang, N. S.Khang, QK-1 ( HN, LE).

Description:— Small evergreen hermaphrodite tree with trunk to 5 m tall and Ø 15 cm; crown loose of diffuse irregular shape. Trunk with dark dirty brownish-gray to light gray, finely rough bark. Young stems, stipules and leaves at the beginning of their development light yellowish-green to pale pink, densely hairy throughout with long soft straight woolly caducous hairs; later completely glabrous. Young branches light green, straight to slightly zigzag, older light dull brownish, often irregularly curved. Buds perulate, purple, ovoid, (2)2.5–4(5) mm long, acute to obtuse, consist of (2)3(4) rigid, coriaceous, glabrous bud scales, 2–4 mm long, 2.5–3.5 mm wide. Stipules paired, large, herbaceous, broadly lanceolate to narrowly ovate, (6.5)8–12(13.5) mm long, (1.5)2–3(4) mm wide, slightly concave, early deciduous, leaving small scars. Leaves alternate, distichous, petiolate; petiole rigid, subterete, dull green to purple, (1.5)2–2.5(3.5) cm long, Ø (1)1.2–1.4(1.6) mm, inflated and slightly curved at base and apex; leaf blade simple, leathery, narrowly ovate, (5)7–10(13) cm long, (2.5)3–4.5(5.5) cm wide, entire along the margin, cordate to suborbicular at the base, shortly attenuate at the apex, dark glossy green above, pale light glaucous-green to almost whitish below; venation pinnate, with 2 more or less prominent basal sub-opposite lateral veins, tertiary veins well distinct on both surfaces, almost perpendicular to main veins. Inflorescence scape naked or bracteate, capitate, axillary, (1)2–3- flowered. Scape (2)4–6(8) mm long, densely hairy, with (0)3–6(7) sterile bracts; sterile bracts distichous, sub-opposite or sub-verticillate (by 3), ovate to narrowly ovate, acute, to 5 mm long, lower sub-glabrous, upper densely hairy and ciliate along the margin; rachis less then 0.5 mm long. Floral bracts (2)3(4), sub-verticillate, ovate, broadly ovate to transversely reniform, (0.5)1–2(2.2) mm long, (0.5)1–3(3.5) mm wide, acute, obtuse or truncate, often crenulate at apex, slightly concave, adaxially glabrous, abaxially densely hairy, ciliate along the margin. Flowers sessile, densely adpressed to each other, actinomorphic, bisexual, 5-merous, with 2-whorled perianth. Floral cup almost flat or hardly concave, outside glabrous, inside between stamens and carpels densely hairy with long straight stiff white hairs; in fruits broadly cup-shaped, glabrous. Sepals 5, red to pink, imbricate, narrowly ovate to ovate, (2.8)3–3.2(3.4) mm long, (1.6)1.8–2(2.2) mm wide, recurved and often revolute along margin; both surfaces glabrous, the margin ciliate, at apex with dense tuft of soft fuzzy hairs. Petals 5, red to pink, sometime whitish along margin in basal part, glabrous, imbricate, (8)9–11(12) mm long, (circinate in bud), basal part (0.8)1–1.2(1.4) mm broad, distally tapering into long ribbon-like prolongation 0.4–0.5 mm wide, spreading, straight or undulate; margins finely irregularly crenulate or incised, often wavy and revolute. Androecium of 5 stamens, with no staminodia; stamens free, arranged in one whorl; filaments cylindrical recurved, (0.8)1–1.2(1.4) mm long, Ø 0.3–0.4 mm; anthers dorsifixed, extrorse, 0.6–0.7 mm long, 0.4–0.5 mm wide, thecae di-sporangiate, bean-shaped before dehiscence, each theca dehiscing by 1 longitudinal slit, with no connective protrusion. Gynoecium, of 2 carpels; ovary semi-inferior, 2-locular, carpels free at apex, fused in basal part; ovules 8(10) per carpel, pendent on axile placenta formed by fused carpellary margins; styles 2, cylindrical, 0.8–1 mm long, purple, slightly recurved, each with indistinct truncate stigma. Fruit semi-woody, pale yellowish to dull brownish, sessile, hemi-syncarpous 2-carpellate capsule, (1.2)1.4–1.6(1.8) cm long and wide, lower part enveloped by woody floral cup, free apex of each carpel erect, apiculate; individual capsules fused to each other forming compact infructescence of 2–3 capsules, dehiscing septicidally above middle by two valves with acute erect apex; woody endocarp loose from semi-woody exocarp. Seeds (6)8(10) per carpel, ejected, obscurely ovoid to indistinctly angled, (3.5)4–5(5.5) mm long, (2)2.2–2.6(3) mm wide, wingless, seed coat black, thick, hard, bony, shiny.

Etymology:—Species name refers to the narrowly ovate shape of leaf blade.

Vernacular name: —Vietnamese: Sừng gỗ nhiều hạt [fruit like woody horn with many seeds].

Habitat, phenology and conservation status:—Small tree to 5 m tall. Primary evergreen broad-leaved and mixed forests with Tsuga dumosa on sandstone at elevations 1850–2000 m a.s.l., usually in wet places in assemblage with Acer sp. , Actinidia sp. , Altingia sp. , Ardisia sp. , Arisaema sp. , Asplenium spp. , Burmannia indica , Daphniphyllum sp. , Euonymus sp. , Impatiens spp. , Lyonia sp. , Magnolia sp. , Oreocharis aurea , Photinia sp. , Polyspora sp. , Polystichum sp. , Rhododendron spp. , Rhodoleia championii , Sargentodoxa cuneata , Schefflera sp. , Schima sp. , Strobilanthes sp. , Utricularia sp. , Vaccinium sp. and Vittaria sp. Locally common. Flowering in March–April, fruiting October– November. Estimated IUCN Red List status DD.

Distribution: —Northwestern Vietnam (Lao Cai province, Bat Xat district). Endemic of northwestern Vietnam.

Notes: —The new species in its general appearance has some superficial similarity with representatives of Loropetalum and Hamamelis widely cultivated as ornamental shrubs and trees. Like species of these genera, as well as Disanthus cercidifolius , our plant has certain significance for ornamental horticulture. It has quite attractive red flowers, long-lasting fruits of unusual shape, pale green or pink young leaves becoming later dark glossy green. It is noteworthy that the same or similar plants were introduced into cultivation in Europe already ten years ago, since 2006. These plants were imported from Vietnam by collectors of the commercial nursery “Crûg Farm Plants” located in northern Wales, UK (Crûg Farm Plants 2017, The Guardian 2017) and later were successively propagated for sale as ornamental plants (Crûg Farm Plants. PLANT LIST 2016 2017). It was reported that this rare ornamental tree was collected in the same locality of Lao Cai province (Bat Xat district, Y Ty commune) of northern Vietnam in 2006 and 2007 (Crûg Farm Plants 2017, The Guardian 2017). The plant was discovered by leading assistance of Mr. Uoc, local guide, who organized a successful collecting tour. It was provisionally named after him, as Uocodendron whartonii hort. Although this name was never validly published it was widely used in horticulture internet blogs including recent picturesque description of botanical excursions in the species locus classicus by UK botanists ( Summers 2016).

Figures

FIGURE 1. Disanthus ovatifolius sp. nov. A—Leafy flowering and fruiting branch. B—Leaf, abaxial surface. C—Leafless flowering branch. D—Leafless fruiting branch. E—Floriferous shoot (bud scales and 3 lower sterile scape bracts removed, 5 apical sterile scape bracts flattened, 3 flowers, each with 3 floral bracts removed). F—Removed bud scales. G—Removed sterile scape bracts. H—Floral bracts, adaxial surface. I—Floral bracts, abaxial surface. J—Intact inflorescence, side view. K—Flower, view from below. L—Sepals, adaxial and abaxial views. M—Petals, adaxial and abaxial views. N—Stamens, frontal view, view from behind and side view. O—Stamens at the end of anthesis. P—Flower disc, tangential and sagittal section. Q—Ripening fruit, side view. R—Ripening fruit, view from above. S—Dehisced fruit with naturally recurved valves, seeds removed. Drawn from the type HN-UBC-68 and paratype QK-1 by L.Averyanov and T. Maisak.

FIGURE 2. Disanthus ovatifolius sp. nov. Digital epitype, 0274/HN-UBC-68 & QK1. Photos of B.H. Quang & K.S. Nguyen, correction and design by L. Averyanov.