Polyalthia taweensis Bunchalee & Leerat., 2021

Bunchalee, Pasakorn, Leeratiwong, Charan & Johnson, David M., 2021, Two new species and a new record of the genus Polyalthia (Annonaceae) from Peninsular Thailand, Phytotaxa 510 (3), pp. 239-250 : 243-246

Polyalthia taweensis Bunchalee & Leerat. , sp. nov. ( Figs. 3 & 4 )

Polyalthia taweensis resembles P. obliqua Hook. f. & Thomson (1855: 138) in leaf shape and size and the shape of the petals, but differs in having supra-axillary or leaf-opposed inflorescences, greenish yellow petals, a differentiated border along the margin on the inner surface of the outer petals, sepals 4.0‒5.0 mm long, and one pedicellar bract. In contrast, P. obliqua has axillary inflorescences on leafy or leafless branches, white petals, the inner with a rosy flush at the base ( Sinclair 1955), the inner surface of the outer petals uniform in texture, sepals ca. 2.0 mm long, and two pedicellar bracts, one attached at the pedicel base and the other at the pedicel midpoint.

Type:— THAILAND. Narathiwat, Ra-Ngae District, Bo Ngo Subdistrict , Ta We Mountain , 20 April 2020 (flower), Leeratiwong 20-1534 (holotype PSU! ; isotype BKF! ).

Shrubs or trees 2.0‒12.0 m tall, d.b.h. up to 18.0 cm, bark smooth, greyish black or grey-brown, primary branching spiral. Young branches glabrous with prominent lenticels. Leaves with petioles 1.5‒3.0 mm long, 1.5‒2.0 mm thick, sunken above; lamina chartaceous, symmetrically or asymmetrically elliptic to slightly oblanceolate and curved inward, 13.0‒20.0 × 3.5‒7.5 cm, base asymmetrically cordate with auricles 0.8‒1.2 mm long, apex acuminate with acumen 10.0‒15.0 mm long, upper side glabrous, lower side glabrescent; midrib prominently grooved above; lateral veins 14‒ 16 per side, arched towards the apex, diverging at 60‒70° from the midrib, festooned loop-forming 2.0‒5.0 mm from the margins; intersecondary veins indistinct; tertiary veins reticulate. Inflorescences supra-axillary or leaf-opposed on leafy branches, 1‒2-flowered; peduncle up to 1 mm long, pedicels 7.0‒10.0 mm long, 0.8−1.0 mm thick, puberulous; bract solitary, triangular or lanceolate, 3.0‒4.0 × 1.2‒1.5 mm, attached from near the pedicel base to near the pedicel apex, apex acute, puberulous outside and glabrous inside. Sepals valvate, light green in vivo, thinly coriaceous, ovate, 4.0‒5.0 × 3.0‒4.0 mm, apex acute to slightly acuminate, puberulous outside and glabrous inside. Petals greenish yellow in vivo, erect or slightly spreading, coriaceous, apex acute, pubescent outside, glabrous inside; outer petals oblong or ovate, 7.0−8.0 × 4.0−5.0 mm, smooth outside, with a raised rugose border along margin inside ( Fig. 3G ); inner petals elliptic, 8.0‒9.0 × 3.0‒4.0 mm, curved inward to the midpoint but with the apex erect ( Fig. 3J ). Stamens pale yellow, cuneate, 1.0‒1.2 × 0.8‒1.0 mm, filament ca. 0.2 mm long; anthers 0.6‒0.8 mm long, anther connective apex flat; androecium 3.0‒4.0 mm in diameter. Carpels 5‒7 per flower, 1.6‒1.8 × 0.5−0.6 mm, pubescent, style rudimentary, stigma obovoid, 0.5‒0.6 mm, pubescent, exceeding the height of the anther connective apices; ovules 2 per carpel, attached laterally. Torus convex, flat at the apex, 3.0‒ 3.5 mm in diameter, 1.0‒ 1.2 mm thick, glabrous. Fruit of ca. 12 monocarps borne on a pedicel ca. 17.0 mm long, 1.8 mm thick. Monocarps green in vivo (immature), subglobose, 12.0‒16.0 × 14.0‒16.0 mm, slightly puckered and verrucose, glabrate, apex rounded, occasionally with an apiculum <1.0 mm long, base rounded, stipes ca. 14.0 mm long, 1.5 mm thick, rugulose, sparsely pubescent to glabrate. Seeds 1‒2 per monocarp, attached laterally in a single row, disk-shaped, 9.8‒12.0 × 8.0‒11.0 × 4.8‒6.1 mm, light brown, slightly shiny, surface densely wrinkled, with a distinct circumferential groove; endosperm rumination pattern not observed.

Distribution and Ecology: —Occurs in tropical rain forest at 120‒250 m in Narathiwat and Yala Provinces of southern Peninsular Thailand. ( Fig. 7 ).

Phenology: —Flowering in February and April, fruiting in February.

Local name: —Thai: Nara morakot.

Etymology: —The specific epithet refers to the locality, Ta We Mountain, where the species was first discovered.

IUCN Conservation status: —The species has been collected from only three localities. There is no information regarding population size at any of the localities. Therefore, the species is considered to be Data Deficient (DD).

Additional specimens examined: — THAILAND. PENINSULAR: Yala, Than To, Ban Chulapon Phattana 7 area, trail from substation up along ridge, 6° 05´N, 101° 23´E, alt. 250 m, 10 February 2004 (flower), Middleton, Phuphat, Pooma & Williams 2900 ( A, BKF, L.3729224 , L.3729128 ) ; Yala, Than To, Hala Bala Wildlife Sanctuary , Khlong Nam Sai , 6° 01´70˝ N, 101° 24´E, alt. 120 m, 14 February 2004 (flower & fruit), Middleton, Phuphat, Pooma & Williams 3083 ( A, L.3729130 ) .

Notes: —Comparative data on P. obliqua used in the diagnosis were taken from Sinclair (1955). Inflorescence position in Annonaceae is usually a conservative feature indicating distinction at the generic level or a marker for groups of related species within a genus, so it is surprising to have this distinction between two otherwise similar species. Turner (2008) documented the same difference, however, between Polyalthia subcordata (Blume) Blume (1830: 71) and Polyalthia elliptica (Blume) Blume (1830: 73) , so inflorescence position appears to be a more variable character within Polyalthia than in other Annonaceae genera. The differentiated border of the outer petals in P. taweensis is an unusual feature; in other Annonaceae such modifications occur only on the inner petals ( van Heusden 1992).

Figures

FIGURE 3. Polyalthia taweensis: A. Habit; B. Close-up of petiole and leaf base (lower side); C. Inflorescence; D. Flower; E. Sepals (outside above, inside below); F. Outside of outer petal; G. Inside of outer petal, showing raised rugose area (arrow); H. Outside of inner petal; I. Inside of inner petal; J. Inner petal, side view showing inward curvature to midpoint (arrow) and erect apex; K. Carpel; L. Stamen, outer view. The illustration was drawn by Nattapong Chomlok from Leeratiwong 20-1534 (BKF).

FIGURE 4. Polyalthia taweensis: A. Leaves and inflorescences; B. Upper surface of leaf base; C. Lower surface of leaf base; D. Inflorescence; E. Sepals (outside on left, inside on light); F. Outsides of petals (outer petal on left, inner petal on right); G. Insides of petals (outer petal showing raised rugose border on left, inner petal on right). A, B & C are from Middleton, Phuphat, Pooma & Williams 2900 (BKF); E, F & G are from Leeratiwong 20-1534 (PSU, spirit material); all photographs by Pasakorn Bunchalee. Photograph in D was taken by Yamilah Sama-ae in Narathiwat, Ra Ngae District, Bo Ngo Subdistrict, Ta We Mountain, 20 April 2020.

FIGURE 7. A. & B. Maps showing distributions of Polyalthia heliopetala (●), P. taweensis (▲) and P. pumila (■) in southern Peninsular Thailand. Map in B is an enlargement of the area shown in the rectangle in A. Maps by Pasakorn Bunchalee.