Polyalthia chalermglinii P.Bunchalee & D.M.Johnson, 2021

Bunchalee, Pasakorn, Johnson, David M., Murray, Nancy A. & Chalermglin, Piya, 2021, Three new species of Polyalthia (Annonaceae) from Thailand and Laos, Phytotaxa 512 (4), pp. 272-282 : 273-276

Polyalthia chalermglinii P.Bunchalee & D.M.Johnson , sp. nov. ( Figs 1 , 2 )

Type:— THAILAND. Nakhon Si Thammarat, Khao Luang , 950–1000 m, 25 May 1968, van Beusekom & Phengklai 1013 (holotype BKF!; isotype L.1763344!) .

Polyalthia chalermglinii resembles P. khaoyaiensis P.Bunchalee & Chantar. in Bunchalee et al. (2019: 172) in having thinly coriaceous, ovate outer petals, fleshy inner petals that are longer than the outer petals and usually 2 ovules per carpel. However, it differs from P. khaoyaiensis in having petioles 1.0–2.0 mm long, pedicels 8.0–12.0 mm long, obovate inner petals, an androecium 4.0–5.0 mm in diameter with stamens 1.4–1.6 mm long, and 12–18 carpels per flower. Polyalthia khaoyaiensis , in contrast, has petioles 2.0–4.0 mm long, pedicels 3.0–5.0 mm long, oblong-lanceolate inner petals, an androecium 7.0–9.0 mm in diameter with stamens 2.0– 2.4 mm long, and 25–35 carpels per flower.

Small trees 1.0–4.0 m tall, d.b.h. up to 10.0 cm, primary branching spiral; bark smooth, blackish brown. Twigs initially rusty brown erect-pubescent, lenticels slightly conspicuous. Leaves subsessile, the petioles 1.0–2.0 mm long, 1.5–1.8 mm thick, slightly grooved above, appressed-pubescent; lamina symmetrically elliptic or oblanceolate, 6.0–12.0 × 2.0– 3.5 cm, base asymmetrically cordate with auricles 0.3–0.5 mm long, apex acute to acuminate with acumen 5.0–8.0 mm long, leaf margin slightly undulate, upper side glabrous, lower side sparsely appressed-puberulous; midrib grooved and glabrous above, pubescent below; lateral veins curved towards the apex, 10–12 veins per side, attached excurrently to midrib at 60–65º, brochidodromous, curving inward 2.5–3.5 mm from margins; interlateral veins present; tertiary veins reticulate. Inflorescences 1(–2)-flowered, leaf-opposed, supra-axillary or on woody tubercles of twigs or trunks, lacking peduncle and rachis; pedicels 8.0–12.0 mm long, 1.0– 1.2 mm thick, rusty brown appressed-pubescent; bract lanceolate, 1.0–1.2 × ca. 0.8 mm, attached near the pedicel base, appressed pubescent outside, glabrous inside; buds ovoid. Sepals pale green in vivo, ovate, valvate, 4.0–5.0 × 3.5–4.0 mm, apex acuminate, pubescent outside, glabrous inside. Petals 6 in 2 whorls, appressed-puberulous outside, glabrous inside; outer petals green to pale yellowish green in vivo, valvate, ovate, 6.0–7.0 × 4.0– 4.5 mm, apex acute; inner petals pale green or yellowish green to orangish red in vivo, valvate, thicker than the outer petals, oblanceolate, 9.0–11.0 × 4.0–5.0 mm, apex acute. Stamens creamy white at anthesis, clavate, 1.4–1.6 × 1.0– 1.2 mm; anthers 0.8–1.0 mm long; anther connective apex truncate; androecium 4.0–5.0 mm in diameter. Carpels 12–18 per flower, 1.6–1.8 × 0.4–0.5 mm, appressed-pubescent; stigma subsessile, obovoid, 0.6–0.8 × 0.4–0.5 mm, erect-puberulous, equal to or slightly higher than anther connective apices; ovules 2 per carpel, with marginal placentation. Torus thickly cushion-shaped, concave in the center, 2.0– 2.5 mm in diameter, 1.8–2.0 mm thick, hairy. Fruit unknown.

Ecology: —Endemic to peninsular Thailand in tropical rain forest at 950–1000 m.

Phenology: —Flowering March–May.

Local name: —Thai: tong laeng khao luang (ต้องแล่งเขาหลวง).

Etymology: —Named in honour of Piya Chalermglin, Thai botanist, horticulturalist and expert on Annonaceae , who assisted in the discovery of this species.

Conservation status: —Data Deficient (DD), because the specimens of Polyalthia chalermglinii were collected from a small area of Khao Luang National Park over 50 years ago, and there are only two collections in herbaria. The population and distribution area of it are still not fully explored.

Additional specimen examined: — THAILAND. Peninsular: Nakhon Si Thammarat, Khao Luang , 1,000 m, 17 Apr 1928, Kerr 15253 ( BK) .

Notes: —The morphological characters of P. chalermglinii are similar to those of P. khaoyaiensis , another higherelevation species ( Bunchalee et al. 2019), but the flowers occur on woody tubercles of the trunk and the suite of vegetative and floral differences summarized in the diagnosis readily separates the two.

Figures

FIGURE 1. Polyalthia chalermglinii: A. Habit; B, C, D & E. Inflorescences on trunk and branch; F. Leaves; G. Leaf (lower side); H. Outer petal, outside (left), inside (right); I. Inner petal, outside (left), inside (right); J. Pedicel, sepal and torus; K. Stamen, outer view; L. Carpel. Photographs taken by Pasakorn Bunchalee.

FIGURE 2. Polyalthia chalermglinii:A & B. Inflorescences on tubercles of trunk and branch; C. Leaf, upper side (left), lower side (right); D. Outer petal, outside (left), inside (right); E. Inner petal, outside (left), inside (centre), and side view (right); F. Stamen, outside; G. Carpel. Illustration by Orathai Kerdkaew.