Loropetalum flavum, 2018

Averyanov, Leonid V., Endress, Peter K., Nguyen, Khang Sinh, Thai, Tran Huy, Maisak, Tatiana V., Averyanova, Anna L. & Diep, Le Ngoc, 2018, Loropetalum flavum (Hamamelidaceae), a new species from northern Vietnam, Phytotaxa 385 (2), pp. 94-100 : 95-98

4. L. flavum Aver., P.K. Endress & K.S. Nguyen , sp. nov. ( Fig. 1 & 2 ).

Diagnosis: —The new species differs from its closest relative L. chinense in arboreous habit, sessile yellow flowers, short peduncles 2–7 mm long, narrowly lanceolate stipules, always axillary inflorescences and large sparsely pubescent leathery leaves 5–12 cm long.

Type: — VIETNAM. Ha Giang province: Quan Ba district, Bat Dai Son commune, Pai Chu Phin village, Bat Dai Son Nature Reserve, ca. 23º07 ʹ 54.9 ʺ N 104º59 ʹ 24.1 ʺ E, 1000–1220 m a.s.l., karstic highly eroded mountains composed of solid marble-like limestone, not common, 16 April 2018, L. Averyanov, Nguyen Sinh Khang, Chuong Quang Ngan, T. Maisak, VR 265 (holotype LE 01042163!, isotypes HN 0000073443!, HN 0000073444!, LE 01042164!, LE 01042165!, LE 01042166!).

Description:—Small evergreen hermaphrodite tree 5–10 m tall with diffuse irregular crown. Trunk and branches dull brownish-gray to pale gray. Branches and leaves more or less densely hairy throughout, with light gray to almost white stellate hairs. Young branches light gray-greenish, straight to slightly zigzag; young leaves dull pale pinkbrownish. Buds perulate, dull pale greenish, narrowly ovoid, obtuse, (2.5–)3–4(–4.5) mm long, consisting of (2–)3(–4) rigid, coriaceous, concave, hairy bud scales, 2–3 mm long, 1.5–2 mm wide. Stipules relatively large, herbaceous, narrowly lanceolate, acuminate, (3–)3.5–4.5(–5) mm long, (0.8–)1(–1.2) mm wide, rather flat, very early deciduous, leaving small scars. Leaves alternate, indistinctly distichous, shortly petiolate; petiole rigid, subterete, dull green to pale grey-green, (1.5–)2–4.5(–5) mm long, (1.2–)1.4–1.8(–2) mm in diameter, straight or slightly recurved; leaf blade simple, leathery, rigid, broadly lanceolate elliptic to narrowly ovate, (5–)6–10(–12) cm long, (2.5–)3–4(–4.5) cm wide, margin entire, base cuneate, apex acuminate, dark green above, pale light glaucous-green to whitish below; venation pinnate, with 2 more or less prominent basal sub-opposite veins and 4–5(–6) pairs of lateral arcuate veins; tertiary veins distinct on both surfaces (immersed adaxially, raised abaxially). Inflorescence axillary, pedunculate, capitate, with (3–)4–10(–12) flowers. Scape bracteate, (2–)3–5(–7) mm long, densely hairy; sterile bracts (2–)3–5(–7) spirally arranged, distant, minute, narrowly to broadly triangular, 0.3–0.5 mm long; rachis 0.4–0.8 mm long; floral bracts absent. Flowers not widely opening, sessile, in a dense head-like cluster, densely adpressed to each other, actinomorphic, bisexual, 4–6-merous, with 2-whorled perianth. Sepals 4–6, yellow, oblong ovate, (1.8–)2–2.4(–2.6) mm long, (1–)1.2–1.4(–1.6) mm wide, recurved and often revolute at apex; glabrous adaxially, outside with dense to sparse white stellate hairs. Petals 3–6(–7), linear-lorate to linear, yellow, glabrous, (9–)12–16(–18) mm long, (0.4–) 0.6–0.9(–1.1) mm broad, erect to spreading, straight to curved (circinate in bud) tapering to the base and apex, early caducous, margins straight and entire. Androecium of (3–)4–6(–7) stamens; stamens free, glabrous, arranged in one whorl; filaments slightly dorso-ventrally flattened, recurved to geniculate, (0.3–)0.4–0.6(–0.7) mm long, (0.25–)0.3– 0.4(–0.45) mm wide; anthers basifixed, (0.6–)0.7–0.8(–0.9) mm long, (0.5–)0.6–0.7(–0.8) mm wide, laterally with 2 rectangular 2-sporangiate thecae dehiscing by 2 valves; connective protrusion prominent, subulate, acuminate, as long as anther or longer, (0.9–)1–1.1(–1.2) long, straight to recurved (occasionally connective protrusion elongate, petaloid). Disc lobes (sometime called disc scales or staminodia) prominent, (2–)4–6(–8), in one whorl (inside staminal whorl), alternate with stamens, fleshy, glabrous, oblate to hemispheric, flattened at apex, (0.3–)0.4–0.5(–0.6) mm in diameter. Gynoecium syncarpous of 2 completely fused carpels; ovary inferior, obconoid, (1.2–)1.4–1.6(–1.8) mm long, (1.2–) 1.4–1.5(–1.6) mm wide, densely hairy, 2-locular, each locule with 1 ovule placed on basal placenta; floral disc almost flat to slightly convex densely hairy with simple and stellate stiff white hairs; styles 2, purplish, separate, very short, erect, cylindrical, straight to slightly recurved, (0.2–)0.25–0.3(–0.35) mm long, each with oblique-capitate, irregularly brush-like coralloid stigma. Fruits and seeds unknown.

Etymology: —Species name refers to the yellow color of flowers.

Habitat, phenology and conservation status: —Small tree to 10 m tall. Primary evergreen broad-leaved and coniferous humid forest with Pseudotsuga sinensis, Xanthocyparis vietnamensis and Pinus kwangtungensis on rocky karstic limestone, at elevations 1000–1220 m a.s.l. Not common. Flowering in March–April. Estimated IUCN Red List status DD.

Distribution: —N. Vietnam (Ha Giang province, Quan Ba district, Bat Dai Son nature reserve). Endemic of northern Vietnam.

Notes: —The new species belongs to the subfamily Hamamelioideae , tribe Loropetaleae ( Li & Bogle 2001) in a group of three genera with stamens having 2-sporangiate thecae and a long horned connective protrusion (see Endress 1989a, b; Hufford & Endress 1989). With its unusual brush-shaped stigma with multicellular branches it fits with Loropetalum ( Endress 1989a) . Embolanthera differs by its winged petals and Maingaya by its long horned staminodia. Loropetalum flavum is well segregated from presently known congeners (see Table 1). The new species is morphologically more or less closely allied to the widespread L. chinense , from which it differs in arboreous life form (vs. shrub 1–3 m tall), narrowly lanceolate stipules (vs. stipules triangular-lanceolate to obovate), lanceolate elliptic to narrowly ovate, prominently acuminate, rigid, leathery leaves, 5–12 cm long (vs. ovate, acute to shortly acuminate, membranaceous leaves, 2–6.5 cm long), axillary inflorescences (vs. inflorescences mostly terminal), peduncles 2–7 mm long (vs. peduncles 8–10 mm), sessile, 4–6-merous, yellow flowers (vs. flowers 4–5-merous, pedicellate, white or red, rarely pale yellow). The new species is also somewhat similar to L. lanceum , from which it differs in stellately pubescent leaves (vs. old leaves glabrescent), many-flowered inflorescences (vs. inflorescences with 4–5 flowers) and 4–6-merous yellow flowers (vs. flowers white, 4-merous). Loropetalum flavum was observed as a typical tree on karstic limestone hills very near to the Chinese border. Hence, the occurrence of this species may be expected in similar habitats in adjacent southern China (southeastern Yunnan and southwestern Guangxi).

Figures

FIGURE 1. Loropetalum flavum Aver., P.K. Endress & K.S. Nguyen.A—Flowering tree in natural habitat. B—Flowering branch. C–E— Inflorescences. F—Flattened branch, adaxial view. G—Flattened branch, abaxial view. H—Petiole. I—Petiole indumentum. J—Leaves, adaxial surface. K—Leaves, abaxial surface. L—Young branchlet. M—Scape. N—Flattened inflorescence, side view. O—Intact flowers, frontal and half-side views. P—Intact flowers, side view. All photos were made from plant prior to preparation of the type herbarium specimens (VR 265). Photos by L. Averyanov and Khang Sinh Nguyen, correction and plate design by L. Averyanov.

FIGURE 2. Loropetalum flavum Aver., P.K. Endress & K.S. Nguyen. A—Pressed inflorescence with half of the flowers removed. B—Scape. C—Flattened flower, side view. D—Flattened flowers with apical part of petals removed, side view. E—Flattened flower with frontal sepals removed, side view. F—Flattened flower with frontal sepals, petals and stamens removed, side view. G—Flattened 4, 5 and 6-merous flowers, view from below. H—Sepals, abaxial side. I—Sepals, adaxial side. J—Flower disc with frontal sepals, petals and stamens removed, side view. K—Intact flower disc. L—Flower disc with disc lobes, frontal and oblique side views (petals and stamens removed). M—Intact stamen, view from abaxial side. N—Stamens, side, abaxial and adaxial views at a different stage of thecae opening. O—Upper part of ovary with styles, side view. P—Upper part of ovary with styles, view from above. Q—Ovary, sagittal section. R— Median leaf vein on abaxial surface of lamina near its base. S—Leaf, abaxial surface. Photos were made from fresh material preserved in alcohol, prior to preparation of type herbarium specimens (VR 265).All photos, correction and plate design by L. Averyanov.