Wikstroemia bokorensis E. Oguri & Tagane, 2017

Oguri, Emiko, Tagane, Shuichiro, Chhang, Phourin, Toyama, Hironori, Murakami, Noriaki & Yahara, Tetsukazu, 2017, Flora of Bokor National Park, Cambodia VI: A new species of Wikstroemia (Thymelaeaceae), W. bokorensis, Phytotaxa 317 (4), pp. 280-285 : 281-283

Wikstroemia bokorensis E. Oguri & Tagane , sp. nov.

Figs. 1 and 2 . Typus. CAMBODIA. Kampot Province, Bokor National Park, 10°39 ʹ 35.42 ʺ N, 104°03 ʹ 03.09 ʺ E, elev. 903 m, 13 May 2012, Toyama H.,

Tagane S., Mishima T., Tagawa K., Zhang M., Chhang P., Iwanaga F., Nagamasu H., Yahara T. 3151 [fl.] (Holotype MAK!, Isotypes

P!, the herbarium of Forest Administration of Cambodia!, KYO!)

Diagnosis. Wikstroemia bokorensis is phenotypically most similar to W. nutans Champion ex Bentham (1853: 195) known from southern China and Vietnam in their elliptic- to ovate-elliptic leaves with a membranous to papery leaf texture and their terminal pendulous inflorescences borne on peduncles that elongate up to 3 cm in length. However, the new species differs from W. nutans by its branches with ± appressed shortly hairy ca. 0.3 mm long and leaves covered with short hairs ca. 0.4 mm long (vs. glabrous), smaller anthers (ca. 1 mm long vs. 1.5–2 mm long), a single disk scale ca. 2 mm long (vs. two scales, each ca. 1 mm long), and a glabrous ovary (vs. pubescent at apex). It also resembles to the widespread species W. androsaemifolia Decaisne (1843: 50) in their elliptic- to ovate-elliptic leaves with papery leaf texture and its inflorescences with long peduncle up to ca. 3 cm long. However, it differs from W. androsaemifolia by its floral pedicels with densely hairy, and a single, broadly obovate disk scale (vs. two, rarely three linear disk scales).

Description. Shrubs 1 m tall; branches reddish brown, terete, ± appressed shortly hairy, hairs simple, hairs ca. 0.3 mm long. Leaves opposite; petiole 2–3 mm long, covered with short hairs, hairs ca. 0.4 mm long; leaf blade adaxially green, abaxially brightly green when fresh, adaxially grayish green, abaxially greenish white to glaucous when dry, elliptic to ovate-elliptic, 2.5–4 × 0.5–2 cm, membranous to thinly papery, very sparsely appressed hairy on both surfaces, hairs ca. 0.4 mm long, base attenuate, apex acute, acuminate or obtuse, margin not cartilaginous, entire; midrib slightly prominent and very sparsely appressed hairy abaxially, hairs ca. 0.4 mm long, secondary veins 7–10 pairs, irregular, often branched, slightly curved towards the margin and then joining the weak intramarginal vein, ca. 0.2 mm apart from the margin, elevated abaxially, glabrous on both surfaces. Inflorescences terminal, umbellate or rarely very shortly racemose, axis of inflorescences <0.2 mm long, pendulous, 3–6 flowered, usually without bracts; peduncle 1.2–3 cm long, slender, slightly flattened, sparsely hairy with simple, hairs ca. 0.3 mm long. Pedicels ca. 1 mm long, densely hairy with simple, hairs ca. 0.3 mm long. Hypanthium yellowish green; floral tube ± cylindrical, 9–12 mm long, covered with sparsely ± appressed simple hairs outside, hairs ca. 0.4 mm long, glabrous inside; lobes 4, elliptic, ca. 3.5 × 2 mm, ± appressed simple hairs on both surfaces, hairs ca. 0.4 mm long. Stamens 8, lower whorl of 4 anthers inserted above middle of hypanthium, upper whorl of 4 anthers inserted near orifice; free portion of filaments ca. 0.3 mm long for lower whorl, ca. 0.1 mm long for upper whorl; anthers linear-oblong, ca. 1 mm long, ca. 0.2 mm diam. Disk scale 1, broadly obovate, ca. 1.5 mm × 0.6 mm, membranous, glabrous. Ovary obovoid, ca. 2 mm long, ca. 0.7 mm in diam., stipitate, glabrous; style ca. 0.2 mm long, stigma subglobose, capitate, ca. 0.4 mm long, ca. 0.6 mm diam., surface papillae. Immature fruits ellipsoid, ca. 1.6 mm long and ca. 0.9 mm diam., black, glabrous, smooth.

Other specimens examined. CAMBODIA. Kampot Province, Bokor National Park, 10°38 ʹ 12.59 ʺ N, 104°02 ʹ 06.37 ʺ E, elev. 1014 m, 5 Dec. 2012, Toyama H. et al. 1604 [ster.] (MAK!, the herbarium of Forest Administration of Cambodia!).

Distribution. Cambodia (currently known only from the type locality, the top plateau of Mt. Bokor).

Habitat and phenology. Wikstroemia bokorensis is rare in moist evergreen forest on the plateau of Mt. Bokor, at ca. 1000 m elevation. The forest is dominated by Tristaniopsis merguensis ( Griffith 1837: 18) Peter G. Wilson & J.T. Waterhouse (1982: 439) , Rhaphiolepis mekongensis ( Cardot 1918: 380) Tagane & H. Toyama (2015: 127), Lithocarpus elephantus (Hance 1875: 365) A. Camus (1931: 40), Macaranga andamanica Kurz (1877: 389) , Antidesma montanum Blume (1827: 1124) , Euonymus indicus B. Heyne ex Wallich (1824: 409) , Garcinia hanburyi Hooker f. (1875: 485) , Garcinia bokorensis H. Toyama & Yahara (2016: 48), and Calophyllum tetrapterum Miquel (1854: 291) ( Tagane et al. 2015, 2017). Flowering specimen was collected in May.

Etymology. The specific epithet bokorensis refers to its type locality, Bokor National Park.

Conservation status. Critically Endangered (CR). During our intensive botanical surveys carried out from the bottom to the top area of southern part of Mt. Bokor in 2011–2013 (surveyed area ca. 270 km 2) ( Tagane et al. 2017), we found only two individuals: one produced flowers and the other was a small non-reproductive sapling. It is qualified as Critically Endangered (CR) using the criterion D of the Red List Categories ( IUCN 2012), although additional individuals may be discovered by more through surveys. The individuals grow in a protected area, but the habitat is very close to a road and resort development areas where it can be easily affected by human disturbance. We need conservation of the species as well as the forests on the plateau in Mt. Bokor.

GenBank accession no. Toyama et al. 1604: LC164891 (ITS), LC164867 (rbcL), LC164915 (trnT-F), LC165002 (rps16), LC164978 (rpl16). Toyama et al. 3151: LC164890 (ITS), LC164866 (rbcL), LC164914 (trnT-F), LC165001 (rps16), LC164977 (rpl16).

Notes. As mentioned above, two species of Wikstroemia , W. meyeniana and W. indica are recorded in Cambodia ( Hô 1992, Peterson 1997, Rogers 2017, Tagane et al. 2017), and W. meyeniana has also been collected from within Bokor National Park. Wikstroemia bokorensis is distinguished from W. meyeniana by its longer peduncle (1.2–3 cm long vs. up to 0.5 cm long), and less flowers per inflorescence (3–6 flowers vs.>6 flowers), and from W. indica by hairy twigs and leaves (vs. glabrous), acute leaf apex (vs. rounded to obtuse), longer peduncle (1.2–3 cm long vs. less than 1 cm long), and 1 disc scale (vs. 2 or 4).

Figures

FIGURE 1. Wikstroemia bokorensis E. Oguri & Tagane, sp. nov. (Toyama et al. 3151): A. branches with pendulous inflorescences; B. 4-flowered inflorescence.

FIGURE 2. Wikstroemia bokorensis E. Oguri & Tagane, sp. nov.: A. flowering branch; B. detail of an abaxial leaf surface and pendulous inflorescence; C. flower; D. flower opened out showing stamens and pistil (an, anther; d, disk scale, composed of a single scale; g, gynoecium; st, stigma); E. disk scale. All materials from Toyama et al. 3151 (MAK). Drawn by M. Murakami (A–C) and E. Oguri (D & E).